Document:

EX-10.9

 Exhibit 10.9 

MIMECAST LIMITED 
 2015
SHARE OPTION AND INCENTIVE PLAN 
  

	SECTION 1.	GENERAL PURPOSE OF THE PLAN; DEFINITIONS 

 The name of the plan is the Mimecast Limited
2015 Share Option and Incentive Plan (the “Plan”). The purpose of the Plan is to encourage and enable the officers, employees, Non-Employee Directors and Consultants of Mimecast Limited (the “Company”) and its Subsidiaries upon
whose judgment, initiative and efforts the Company largely depends for the successful conduct of its business to acquire a proprietary interest in the Company. It is anticipated that providing such persons with a direct stake in the Company’s
welfare will assure a closer identification of their interests with those of the Company and its shareholders, thereby stimulating their efforts on the Company’s behalf and strengthening their desire to remain with the Company. 

The following terms shall be defined as set forth below: 

“Act” means the Securities Act of 1933, as amended, and the rules and regulations thereunder. 

“Administrator” means either the Board or the compensation committee of the Board or a similar committee performing the
functions of the compensation committee and which is comprised of not less than two Non-Employee Directors who are independent. 

“Appendix” means an appendix to the Plan. 

“Award” or “Awards,” except where referring to a particular category of grant under the Plan, shall include
Incentive Share Options, Non-Qualified Share Options, Share Appreciation Rights, Restricted Share Units, Restricted Share Awards, Unrestricted Share Awards, Cash-Based Awards, Performance Share Awards and Dividend Equivalent Rights. 

“Award Certificate” means a written or electronic document setting forth the terms and provisions applicable to an Award
granted under the Plan. Each Award Certificate is subject to the terms and conditions of the Plan. 
 “Board” means the
Board of Directors of the Company. 
 “Cash-Based Award” means an Award entitling the recipient to receive a
cash-denominated payment. 
 “Code” means the Internal Revenue Code of 1986, as amended, and any successor Code, and
related rules, regulations and interpretations. 
 “Consultant” means any natural person that provides bona fide services
to the Company, and such services are not in connection with the offer or sale of securities in a capital-raising transaction and do not directly or indirectly promote or maintain a market for the Company’s securities. 

 “Covered Employee” means an employee who is a “Covered Employee”
within the meaning of Section 162(m) of the Code. 
 “Dividend Equivalent Right” means an Award entitling the grantee
to receive credits based on cash dividends that would have been paid on the Shares specified in the Dividend Equivalent Right (or other award to which it relates) if such Shares had been issued to and held by the grantee. 

“Effective Date” means the date on which the Plan becomes effective as set forth in Section 22. 

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder. 

“Fair Market Value” of the Shares on any given date means the fair market value of the Shares determined in good faith by the
Administrator; provided, however, that if the Shares are admitted to quotation on the National Association of Securities Dealers Automated Quotation System (“NASDAQ”), NASDAQ Global Market or another national securities exchange, the
determination shall be made by reference to market quotations. If there are no market quotations for such date, the determination shall be made by reference to the last date preceding such date for which there are market quotations; provided
further, however, that if the date for which Fair Market Value is determined is the first day when trading prices for the Shares are reported on a national securities exchange, the Fair Market Value shall be the “Price to the Public” (or
equivalent) set forth on the cover page for the final prospectus relating to the Company’s Initial Public Offering. 

“Incentive Share Option” means any Share Option designated and qualified as an “incentive stock option” as defined
in Section 422 of the Code. 
 “Initial Public Offering” means the first underwritten, firm commitment public
offering pursuant to an effective registration statement under the Act covering the offer and sale by the Company of its equity securities, or such other event as a result of or following which the Shares shall be publicly held. 

“Non-Employee Director” means a member of the Board who is not also an employee of the Company or any Subsidiary. 

“Non-Qualified Share Option” means any Share Option that is not an Incentive Share Option. 

“Option” or “Share Option” means any option to purchase Shares granted pursuant to Section 6. 

“Ordinary Shares” means the ordinary shares of the Company. 

  
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 “Performance-Based Award” means any Restricted Share Award, Restricted Share
Units, Performance Share Award or Cash-Based Award granted to a Covered Employee that is intended to qualify as “performance-based compensation” under Section 162(m) of the Code and the regulations promulgated thereunder. 

“Performance Criteria” means the criteria that the Administrator selects for purposes of establishing the Performance Goal or Performance
Goals for an individual for a Performance Cycle. The Performance Criteria (which shall be applicable to the organizational level specified by the Administrator, including, but not limited to, the Company or a unit, division, group, or Subsidiary of
the Company) that will be used to establish Performance Goals are limited to the following: total shareholder return; expense levels; cash flow (including, but not limited to, operating cash flow and free cash flow); business development and
financing milestones; earnings before interest, taxes, depreciation and amortization, or any elements thereof; net income (loss) (either before or after interest, taxes, depreciation and/or amortization); changes in the market price of the
Company’s ordinary shares; economic value-added; sales or revenue; acquisitions or strategic transactions; operating income (loss); return on capital, assets, equity, or investment; shareholder returns; return on sales; gross or net profit
levels; productivity; expense; margins; operating efficiency; customer satisfaction; working capital; earnings (loss) per Share; sales or market shares and number of customers; annual spend estimate for new customers signed; number of billable
awards; billings and billings retention rate, any of which may be measured either in absolute terms or as compared to any incremental increase or as compared to results of a peer group. The Committee may appropriately adjust any evaluation
performance under a Performance Criterion to exclude any of the following events that occurs during a Performance Cycle: (i) asset write-downs or impairments, (ii) litigation or claim judgments or settlements, (iii) the effect of
changes in tax law, accounting principles or other such laws or provisions affecting reporting results, (iv) accruals for reorganizations and restructuring programs, and (v) any item of an unusual nature or of a type that indicates
infrequency of occurrence, or both, including those described in the Financial Accounting Standards Board’s authoritative guidance and/or in management’s discussion and analysis of financial condition of operations appearing the
Company’s annual report to shareholders for the applicable year. 
 “Performance Cycle” means one or more periods of
time, which may be of varying and overlapping durations, as the Administrator may select, over which the attainment of one or more Performance Criteria will be measured for the purpose of determining a grantee’s right to and the payment of a
Restricted Share Award, Restricted Share Units, Performance Share Award or Cash-Based Award, the vesting and/or payment of which is subject to the attainment of one or more Performance Goals. Each such period shall not be less than 12 months.

 “Performance Goals” means, for a Performance Cycle, the specific goals established in writing by the Administrator
for a Performance Cycle based upon the Performance Criteria.  
 “Performance Share Award” means an Award entitling
the recipient to acquire Shares upon the attainment of specified performance goals. 
 “Restricted Shares” means the Shares
underlying a Restricted Share Award that remain subject to a risk of forfeiture or the Company’s right of repurchase. 

  
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 “Restricted Share Award” means an Award of Restricted Shares subject to such
restrictions and conditions as the Administrator may determine at the time of grant. 
 “Restricted Share Units”
means an Award of share units subject to such restrictions and conditions as the Administrator may determine at the time of grant. 

“Sale Event” means (i) the sale of all or substantially all of the assets of the Company on a consolidated basis to an
unrelated person or entity, (ii) a merger, reorganization or consolidation pursuant to which the holders of the Company’s outstanding voting power and outstanding shares immediately prior to such transaction do not own a majority of the
outstanding voting power and outstanding shares or other equity interests of the resulting or successor entity (or its ultimate parent, if applicable) immediately upon completion of such transaction, (iii) the sale of all of the Shares of the
Company to an unrelated person, entity or group thereof acting in concert, or (iv) any other transaction in which the owners of the Company’s outstanding voting power immediately prior to such transaction do not own at least a majority of
the outstanding voting power of the Company or any successor entity immediately upon completion of the transaction other than as a result of the acquisition of securities directly from the Company. 

“Sale Price” means the value as determined by the Administrator of the consideration payable, or otherwise to be
received by shareholders, per Share pursuant to a Sale Event. 
 “Section 409A” means Section 409A of the Code
and the regulations and other guidance promulgated thereunder. 
 “Shares” means the Ordinary Shares, subject to
adjustments pursuant to Section 3. 
 “Share Appreciation Right” means an Award entitling the recipient to receive
Shares having a value equal to the excess of the Fair Market Value of the Shares on the date of exercise over the exercise price of the Share Appreciation Right multiplied by the number of Shares with respect to which the Share Appreciation Right
shall have been exercised. 
 “Subsidiary” means any corporation or other entity (other than the Company) in which
the Company has at least a 50 percent interest, either directly or indirectly. 
 “Ten Percent Owner” means an
employee who owns or is deemed to own (by reason of the attribution rules of Section 424(d) of the Code) more than 10 percent of the combined voting power of all classes of shares of the Company or any parent or subsidiary corporation. 

 “Unrestricted Share Award” means an Award of Shares free of any restrictions. 

 

	SECTION 2.	ADMINISTRATION OF PLAN; ADMINISTRATOR AUTHORITY TO SELECT GRANTEES AND DETERMINE AWARDS 

(a) Administration of Plan. The Plan shall be administered by the Administrator. 

(b) Powers of Administrator. The Administrator shall have the power and authority to grant Awards consistent with the terms of the
Plan, including the power and authority: 
 (i) to select the individuals to whom Awards may from time to time be granted; 

  
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 (ii) to determine the time or times of grant, and the extent, if any, of Incentive Share Options,
Non-Qualified Share Options, Share Appreciation Rights, Restricted Share Awards, Restricted Share Units, Unrestricted Share Awards, Cash-Based Awards, Performance Share Awards and Dividend Equivalent Rights, or any combination of the foregoing,
granted to any one or more grantees; 
 (iii) to determine the number of Shares to be covered by any Award; 

(iv) to determine and modify from time to time the terms and conditions, including restrictions, not inconsistent with the terms of the Plan,
of any Award, which terms and conditions may differ among individual Awards and grantees, and to approve the forms of Award Certificates; 

(v) to accelerate at any time the exercisability or vesting of all or any portion of any Award; 

(vi) subject to the provisions of Section 6(c), to extend at any time the period in which Share Options may be exercised; 

(vii) at any time to adopt, alter and repeal such rules, guidelines and practices for administration of the Plan and for its own acts and
proceedings as it shall deem advisable; 
 (viii) to interpret the terms and provisions of the Plan and any Award (including related written
instruments); 
 (ix) to make all determinations it deems advisable for the administration of the Plan; and 

(x) to decide all disputes arising in connection with the Plan; and to otherwise supervise the administration of the Plan. 

All decisions and interpretations of the Administrator shall be binding on all persons, including the Company and Plan grantees. 

(c) Delegation of Authority to Grant Awards. Subject to applicable law, the Administrator, in its discretion, may delegate to the Chief
Executive Officer of the Company all or part of the Administrator’s authority and duties with respect to the granting of Awards to individuals who are (i) not subject to the reporting and other provisions of Section 16 of the Exchange
Act and (ii) not Covered Employees. Any such delegation by the Administrator shall include a limitation as to the number of Shares underlying Awards that may be granted during the period of the delegation and shall contain guidelines as to the
determination of the exercise price and the vesting criteria. The Administrator may revoke or amend the terms of a delegation at any time but such action shall not invalidate any prior actions of the Administrator’s delegate or delegates that
were consistent with the terms of the Plan. 

  
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 (d) Award Certificate. Awards under the Plan shall be evidenced by Award Certificates that
set forth the terms, conditions and limitations for each Award which may include, without limitation, the term of an Award and the provisions applicable in the event employment or service terminates. 

(e) Indemnification. Neither the Board nor the Administrator, nor any member of either or any delegate thereof, shall be liable for any
act, omission, interpretation, construction or determination made in good faith in connection with the Plan, and the members of the Board and the Administrator (and any delegate thereof) shall be entitled in all cases to indemnification and
reimbursement by the Company in respect of any claim, loss, damage or expense (including, without limitation, reasonable attorneys’ fees) arising or resulting therefrom to the fullest extent permitted by law and/or under the Company’s
articles or bylaws or any directors’ and officers’ liability insurance coverage which may be in effect from time to time and/or any indemnification agreement between such individual and the Company. 

(f) Foreign Award Recipients. Notwithstanding any provision of the Plan to the contrary, in order to comply with the laws in other
countries in which the Company and its Subsidiaries operate or have employees or other individuals eligible for Awards, the Administrator, in its sole discretion, shall have the power and authority to: (i) determine which Subsidiaries shall be
covered by the Plan; (ii) determine which individuals outside the United States are eligible to participate in the Plan; (iii) modify the terms and conditions of any Award granted to individuals outside the United States to comply with
applicable foreign laws, including by setting out such terms and conditios in an Appendix; (iv) establish subplans and modify exercise procedures and other terms and procedures, to the extent the Administrator determines such actions to be
necessary or advisable (and such subplans and/or modifications shall be attached to this Plan as appendices); provided, however, that no such subplans and/or modifications shall increase the share limitations contained in Section 3(a) hereof;
and (v) take any action, before or after an Award is made, that the Administrator determines to be necessary or advisable to obtain approval or comply with any local governmental regulatory exemptions or approvals. Notwithstanding the
foregoing, the Administrator may not take any actions hereunder, and no Awards shall be granted, that would violate the Exchange Act or any other applicable United States securities law, the Code, or any other applicable United States governing
statute or law. 
  

	SECTION 3.	SHARES ISSUABLE UNDER THE PLAN; MERGERS; SUBSTITUTION 

 (a) Shares Issuable. The
maximum number of Shares reserved and available for issuance under the Plan shall be [                ]1 Shares (the
“Initial Limit”), subject to adjustment as provided in this Section 3, plus on January 1, 2016 and each January 1 thereafter, the number of Shares reserved and available for issuance under the Plan shall be cumulatively
increased by five percent of the number of Shares issued and outstanding on the immediately preceding December 31 or such lesser number of Shares determined by the Administrator (the “Annual Increase”). The Shares underlying any
Awards that are forfeited, canceled, held back upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of 

 

	1 	 A number equal to 10% of the post-IPO outstanding. 

  
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Shares or otherwise terminated under this Plan (other than by exercise) shall be added back to the Shares available for issuance under the Plan. In the event the Company repurchases Shares on the
open market, such Shares shall not be added to the Shares available for issuance under the Plan. Subject to the overall limitation, (a) the maximum aggregate number of Shares that may be issued in the form of Incentive Share Options shall not
exceed the Initial Limit cumulatively increased on January 1, 2016 and on each January 1 thereafter by the lesser of the Annual Increase for such year or 3,000,000 Shares and (b) Shares may be issued up to the maximum number of Shares
available under the Plan pursuant to any type or types of Award; provided, however, that Share Options or Share Appreciation Rights with respect to no more than
[                ]2 Shares may be granted to any one individual grantee during any one calendar year period. The
Shares available for issuance under the Plan may be authorized but unissued Shares or Shares reacquired by the Company. 
 (b) Changes in
Shares. Subject to Section 3(c) hereof, if, as a result of any reorganization, recapitalization, reclassification, share dividend, share split, reverse share split or other similar change in the Company’s share capital, the outstanding
Shares are increased or decreased or are exchanged for a different number or kind of shares or other securities of the Company, or additional shares or new or different shares or other securities of the Company or other non-cash assets are
distributed with respect to such Shares or other securities, or, if, as a result of any merger or consolidation, sale of all or substantially all of the assets of the Company, the outstanding Shares are converted into or exchanged for securities of
the Company or any successor entity (or a parent or subsidiary thereof), the Administrator shall make an appropriate or proportionate adjustment in (i) the maximum number of Shares reserved for issuance under the Plan, including the maximum
number of Shares that may be issued in the form of Incentive Share Options, (ii) the number of Share Options or Share Appreciation Rights that can be granted to any one individual grantee and the maximum number of Shares that may be granted
under a Performance-Based Award, (iii) the number and kind of Shares or other securities subject to any then outstanding Awards under the Plan, (iv) the repurchase price, if any, per Share subject to each outstanding Restricted Share
Award, and (v) the exercise price for each Share subject to any then outstanding Share Options and Share Appreciation Rights under the Plan, without changing the aggregate exercise price (i.e., the exercise price multiplied by the number of
Share Options and Share Appreciation Rights) as to which such Share Options and Share Appreciation Rights remain exercisable. The Administrator shall also make equitable or proportionate adjustments in the number of Shares subject to outstanding
Awards and the exercise price and the terms of outstanding Awards to take into consideration cash dividends paid other than in the ordinary course or any other extraordinary corporate event. The adjustment by the Administrator shall be final,
binding and conclusive. No fractional Shares shall be issued under the Plan resulting from any such adjustment, but the Administrator in its discretion may make a cash payment in lieu of fractional Shares. 

(c) Mergers and Other Transactions. In the case of and subject to the consummation of a Sale Event, the parties thereto may cause the
assumption or continuation of Awards theretofore granted by the successor entity, or the substitution of such Awards with new Awards 

 

	2 	 A number approximately equal to $15 million Black-Scholes value. 

  
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of the successor entity or parent thereof, with appropriate adjustment as to the number and kind of shares and, if appropriate, the per Share exercise prices, as such parties shall agree. To the
extent the parties to such Sale Event do not provide for the assumption, continuation or substitution of Awards, upon the effective time of the Sale Event, the Plan and all outstanding Awards granted hereunder shall terminate. In such case, except
as may be otherwise provided in the relevant Award Certificate, all Options and Share Appreciation Rights that are not exercisable immediately prior to the effective time of the Sale Event shall become fully exercisable as of the effective time of
the Sale Event, all other Awards with time-based vesting, conditions or restrictions shall become fully vested and nonforfeitable as of the effective time of the Sale Event, and all Awards with conditions and restrictions relating to the attainment
of performance goals may become vested and nonforfeitable in connection with a Sale Event in the Administrator’s discretion or to the extent specified in the relevant Award Certificate. In the event of such termination, (i) the Company
shall have the option (in its sole discretion) to make or provide for a cash payment to the grantees holding Options and Share Appreciation Rights, in exchange for the cancellation thereof, in an amount equal to the difference between (A) the
Sale Price multiplied by the number of Shares subject to outstanding Options and Share Appreciation Rights (to the extent then exercisable at prices not in excess of the Sale Price) and (B) the aggregate exercise price of all such outstanding
Options and Share Appreciation Rights; or (ii) each grantee shall be permitted, within a specified period of time prior to the consummation of the Sale Event as determined by the Administrator, to exercise all outstanding Options and Share
Appreciation Rights (to the extent then exercisable) held by such grantee. 
  

	SECTION 4.	MAXIMUM AWARDS TO NON-EMPLOYEE DIRECTORS 

 Notwithstanding anything to the contrary in
this Plan, the value of all Awards awarded under this Plan and all other cash compensation paid by the Company to any Non-Employee Director in any calendar year shall not exceed $1,000,000. For the purpose of this limitation, the value of any Award
shall be its grant date fair value, as determined in accordance with Financial Accounting Standards Board Accounting Standards Codification 718 but excluding the impact of estimated forfeitures related to service-based vesting provisions. 

 

	SECTION 5.	ELIGIBILITY 

 Grantees under the Plan will be such full or part-time officers and other
employees, Non-Employee Directors and Consultants of the Company and its Subsidiaries as are selected from time to time by the Administrator in its sole discretion. 
  

	SECTION 6.	SHARE OPTIONS 

 (a) Award of Share Options. The Administrator may grant Share
Options under the Plan. Any Share Option granted under the Plan shall be in such form as the Administrator may from time to time approve. 

Share Options granted under the Plan may be either Incentive Share Options or Non-Qualified Share Options. Incentive Share Options may be
granted only to employees of the Company or any Subsidiary that is a “subsidiary corporation” within the meaning of Section 424(f) of the Code. To the extent that any Option does not qualify as an Incentive Share Option, it shall be
deemed a Non-Qualified Share Option. 

  
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 Share Options granted pursuant to this Section 6 shall be subject to the following terms and
conditions and shall contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Administrator shall deem desirable. If the Administrator so determines, Share Options may be granted in lieu of cash compensation
at the optionee’s election, subject to such terms and conditions as the Administrator may establish. 
 (b) Exercise Price. The
exercise price per share for the Shares covered by a Share Option granted pursuant to this Section 6 shall be determined by the Administrator at the time of grant but shall not be less than 100 percent of the Fair Market Value on the date of
grant. In the case of an Incentive Share Option that is granted to a Ten Percent Owner, the option price of such Incentive Share Option shall be not less than 110 percent of the Fair Market Value on the grant date. 

(c) Option Term. The term of each Share Option shall be fixed by the Administrator, but no Share Option shall be exercisable more than
ten years after the date the Share Option is granted. In the case of an Incentive Share Option that is granted to a Ten Percent Owner, the term of such Share Option shall be no more than five years from the date of grant. 

(d) Exercisability; Rights of a Shareholder. Share Options shall become exercisable at such time or times, whether or not in
installments, as shall be determined by the Administrator at or after the grant date. The Administrator may at any time accelerate the exercisability of all or any portion of any Share Option. An optionee shall have the rights of a shareholder only
as to shares acquired upon the exercise of a Share Option and not as to unexercised Share Options. 
 (e) Method of Exercise. Share
Options may be exercised in whole or in part, by giving written or electronic notice of exercise to the Company, specifying the number of Shares to be purchased. Payment of the purchase price may be made by one or more of the following methods
except to the extent otherwise provided in the Option Award Certificate: 
 (i) In cash, by certified or bank check or other instrument
acceptable to the Administrator; 
 (ii) Through the delivery (or attestation to the ownership following such procedures as the Company may
prescribe) of Shares that are not then subject to restrictions under any Company plan. Such surrendered Shares shall be valued at Fair Market Value on the exercise date; 

(iii) By the optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to
promptly deliver to the Company cash or a check payable and acceptable to the Company for the purchase price; provided that in the event the optionee chooses to pay the purchase price as so provided, the optionee and the broker shall comply with
such procedures and enter into such agreements of indemnity and other agreements as the Company shall prescribe as a condition of such payment procedure; or 

(iv) With respect to Share Options that are not Incentive Share Options, by a “net exercise” arrangement pursuant to which the
Company will reduce the number of Shares issuable upon exercise by the largest whole number of Shares with a Fair Market Value that does not exceed the aggregate exercise price. 

  
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 Payment instruments will be received subject to collection. The transfer to the optionee on the records of the
Company or of the transfer agent of the Shares to be purchased pursuant to the exercise of a Share Option will be contingent upon receipt from the optionee (or a purchaser acting in his stead in accordance with the provisions of the Share Option) by
the Company of the full purchase price for such shares and the fulfillment of any other requirements contained in the Option Award Certificate or applicable provisions of laws (including the satisfaction of any withholding taxes that the Company is
obligated to withhold with respect to the optionee). In the event an optionee chooses to pay the purchase price by previously-owned Shares through the attestation method, the number of Shares transferred to the optionee upon the exercise of the
Share Option shall be net of the number of attested Shares. In the event that the Company establishes, for itself or using the services of a third party, an automated system for the exercise of Share Options, such as a system using an internet
website or interactive voice response, then the paperless exercise of Share Options may be permitted through the use of such an automated system. 

(f) Annual Limit on Incentive Share Options. To the extent required for “incentive stock option” treatment under
Section 422 of the Code, the aggregate Fair Market Value (determined as of the time of grant) of the Shares with respect to which Incentive Share Options granted under this Plan and any other plan of the Company or its parent and subsidiary
corporations become exercisable for the first time by an optionee during any calendar year shall not exceed $100,000. To the extent that any Share Option exceeds this limit, it shall constitute a Non-Qualified Share Option. 

 

	SECTION 7.	SHARE APPRECIATION RIGHTS 

 (a) Award of Share Appreciation Rights. The
Administrator may grant Share Appreciation Rights under the Plan. A Share Appreciation Right is an Award entitling the recipient to receive Shares having a value equal to the excess of the Fair Market Value of a Share on the date of exercise over
the exercise price of the Share Appreciation Right multiplied by the number of Shares with respect to which the Share Appreciation Right shall have been exercised. 

(b) Exercise Price of Share Appreciation Rights. The exercise price of a Share Appreciation Right shall not be less than 100 percent of
the Fair Market Value of the Shares on the date of grant. 
 (c) Grant and Exercise of Share Appreciation Rights. Share Appreciation
Rights may be granted by the Administrator independently of any Share Option granted pursuant to Section 6 of the Plan. 
 (d) Terms
and Conditions of Share Appreciation Rights. Share Appreciation Rights shall be subject to such terms and conditions as shall be determined from time to time by the Administrator. The term of a Share Appreciation Right may not exceed ten years.

  
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	SECTION 8.	RESTRICTED SHARE AWARDS 

 (a) Nature of Restricted Share Awards. The Administrator
may grant Restricted Share Awards under the Plan. A Restricted Share Award is any Award of Restricted Shares subject to such restrictions and conditions as the Administrator may determine at the time of grant. Conditions may be based on continuing
employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among
individual Awards and grantees. 
 (b) Rights as a Shareholder. Upon the grant of the Restricted Share Award and payment of any
applicable purchase price, a grantee shall have the rights of a shareholder with respect to the voting of the Restricted Shares and receipt of dividends; provided that if the lapse of restrictions with respect to the Restricted Share Award is tied
to the attainment of performance goals, any dividends paid by the Company during the performance period shall accrue and shall not be paid to the grantee until and to the extent the performance goals are met with respect to the Restricted Share
Award. Unless the Administrator shall otherwise determine, (i) uncertificated Restricted Shares shall be accompanied by a notation on the records of the Company or the transfer agent to the effect that they are subject to forfeiture until such
Restricted Shares are vested as provided in Section 8(d) below, and (ii) certificated Restricted Shares shall remain in the possession of the Company until such Restricted Shares are vested as provided in Section 8(d) below, and the
grantee shall be required, as a condition of the grant, to deliver to the Company such instruments of transfer as the Administrator may prescribe. 

(c) Restrictions. Restricted Shares may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of except as
specifically provided herein or in the Restricted Share Award Certificate. Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 19 below, in writing after the Award is issued, if a
grantee’s employment (or other service relationship) with the Company and its Subsidiaries terminates for any reason, any Restricted Shares that have not vested at the time of termination shall automatically and without any requirement of
notice to such grantee from or other action by or on behalf of, the Company be deemed to have been reacquired by the Company at its original purchase price (if any) from such grantee or such grantee’s legal representative simultaneously with
such termination of employment (or other service relationship), and thereafter shall cease to represent any ownership of the Company by the grantee or rights of the grantee as a shareholder. Following such deemed reacquisition of Restricted Shares
that are represented by physical certificates, a grantee shall surrender such certificates to the Company upon request without consideration. 

(d) Vesting of Restricted Shares. The Administrator at the time of grant shall specify the date or dates and/or the attainment of
pre-established performance goals, objectives and other conditions on which the non-transferability of the Restricted Shares and the Company’s right of repurchase or forfeiture shall lapse. Subsequent to such date or dates and/or the attainment
of such pre-established performance goals, objectives and other conditions, the shares on which all restrictions have lapsed shall no longer be Restricted Shares and shall be deemed “vested.” 

  
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	SECTION 9.	RESTRICTED SHARE UNITS 

 (a) Nature of Restricted Share Units. The Administrator
may grant Restricted Share Units under the Plan. A Restricted Share Unit is an Award of share units that may be settled in Shares upon the satisfaction of such restrictions and conditions at the time of grant. Conditions may be based on continuing
employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among
individual Awards and grantees. Except in the case of Restricted Share Units with a deferred settlement date that complies with Section 409A, at the end of the vesting period, the Restricted Share Units, to the extent vested, shall be settled
in the form of Shares. Restricted Share Units with deferred settlement dates are subject to Section 409A and shall contain such additional terms and conditions as the Administrator shall determine in its sole discretion in order to comply with
the requirements of Section 409A. 
 (b) Election to Receive Restricted Share Units in Lieu of Compensation. The Administrator
may, in its sole discretion, permit a grantee to elect to receive a portion of future cash compensation otherwise due to such grantee in the form of an award of Restricted Share Units. Any such election shall be made in writing and shall be
delivered to the Company no later than the date specified by the Administrator and in accordance with Section 409A and such other rules and procedures established by the Administrator. Any such future cash compensation that the grantee elects
to defer shall be converted to a fixed number of Restricted Share Units based on the Fair Market Value of the Shares on the date the compensation would otherwise have been paid to the grantee if such payment had not been deferred as provided herein.
The Administrator shall have the sole right to determine whether and under what circumstances to permit such elections and to impose such limitations and other terms and conditions thereon as the Administrator deems appropriate. Any Restricted Share
Units that are elected to be received in lieu of cash compensation shall be fully vested, unless otherwise provided in the Award Certificate. 

(c) Rights as a Shareholder. A grantee shall have the rights as a shareholder only as to Shares acquired by the grantee upon settlement
of Restricted Share Units; provided, however, that the grantee may be credited with Dividend Equivalent Rights with respect to the share units underlying his Restricted Share Units, subject to the provisions of Section 14 and such terms and
conditions as the Administrator may determine. 
 (d) Termination. Except as may otherwise be provided by the Administrator either in
the Award Certificate or, subject to Section 19 below, in writing after the Award is issued, a grantee’s right in all Restricted Share Units that have not vested shall automatically terminate upon the grantee’s termination of
employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason. 
  

	SECTION 10.	UNRESTRICTED SHARE AWARDS 

 Grant or Sale of Unrestricted Shares. The
Administrator may grant (or sell at par value or such higher purchase price determined by the Administrator) an Unrestricted Share Award under the Plan. An Unrestricted Share Award is an Award pursuant to which the grantee may

  
 12 

 
receive Shares free of any restrictions under the Plan. Unrestricted Share Awards may be granted in respect of past services or other valid consideration, or in lieu of cash compensation due to
such grantee. 
  

	SECTION 11.	CASH-BASED AWARDS 

 Grant of Cash-Based Awards. The Administrator may grant
Cash-Based Awards under the Plan. A Cash-Based Award is an Award that entitles the grantee to a payment in cash upon the attainment of specified Performance Goals. The Administrator shall determine the maximum duration of the Cash-Based Award, the
amount of cash to which the Cash-Based Award pertains, the conditions upon which the Cash-Based Award shall become vested or payable, and such other provisions as the Administrator shall determine. Each Cash-Based Award shall specify a
cash-denominated payment amount, formula or payment ranges as determined by the Administrator. Payment, if any, with respect to a Cash-Based Award shall be made in accordance with the terms of the Award and may be made in cash. 

 

	SECTION 12.	PERFORMANCE SHARE AWARDS 

 (a) Nature of Performance Share Awards. The
Administrator may grant Performance Share Awards under the Plan. A Performance Share Award is an Award entitling the grantee to receive Shares upon the attainment of performance goals. The Administrator shall determine whether and to whom
Performance Share Awards shall be granted, the performance goals, the periods during which performance is to be measured, which may not be less than one year except in the case of a Sale Event, and such other limitations and conditions as the
Administrator shall determine. 
 (b) Rights as a Shareholder. A grantee receiving a Performance Share Award shall have the rights of
a shareholder only as to Shares actually received by the grantee under the Plan and not with respect to Shares subject to the Award but not actually received by the grantee. A grantee shall be entitled to receive Shares under a Performance Share
Award only upon satisfaction of all conditions specified in the Performance Share Award Certificate (or in a performance plan adopted by the Administrator). 

(c) Termination. Except as may otherwise be provided by the Administrator either in the Award agreement or, subject to Section 19
below, in writing after the Award is issued, a grantee’s rights in all Performance Share Awards shall automatically terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its
Subsidiaries for any reason. 
  

	SECTION 13.	PERFORMANCE-BASED AWARDS TO COVERED EMPLOYEES 

 (a) Performance-Based Awards. The
Administrator may grant one or more Performance-Based Awards in the form of a Restricted Share Award, Restricted Share Units, Performance Share Awards or Cash-Based Award payable upon the attainment of Performance Goals that are established by the
Administrator and relate to one or more of the Performance Criteria, in each case on a specified date or dates or over any period or periods determined by the Administrator. The Administrator shall define in an objective fashion the manner of
calculating the Performance Criteria it selects to use for any Performance Cycle. Depending on the 

  
 13 

 
Performance Criteria used to establish such Performance Goals, the Performance Goals may be expressed in terms of overall Company performance or the performance of a division, business unit, or
an individual. Each Performance-Based Award shall comply with the provisions set forth below. 
 (b) Grant of Performance-Based
Awards. With respect to each Performance-Based Award granted to a Covered Employee, the Administrator shall select, within the first 90 days of a Performance Cycle (or, if shorter, within the maximum period allowed under Section 162(m) of
the Code) the Performance Criteria for such grant, and the Performance Goals with respect to each Performance Criterion (including a threshold level of performance below which no amount will become payable with respect to such Award). Each
Performance-Based Award will specify the amount payable, or the formula for determining the amount payable, upon achievement of the various applicable performance targets. The Performance Criteria established by the Administrator may be (but need
not be) different for each Performance Cycle and different Performance Goals may be applicable to Performance-Based Awards to different Covered Employees. 

(c) Payment of Performance-Based Awards. Following the completion of a Performance Cycle, the Administrator shall meet to review and
certify in writing whether, and to what extent, the Performance Goals for the Performance Cycle have been achieved and, if so, to also calculate and certify in writing the amount of the Performance-Based Awards earned for the Performance Cycle. The
Administrator shall then determine the actual size of each Covered Employee’s Performance-Based Award. 
 (d) Maximum Award
Payable. The maximum Performance-Based Award payable to any one Covered Employee under the Plan for a Performance Cycle is [                ]3 Shares (subject to adjustment as provided in Section 3(b) hereof) or $15,000,000 in the case of a Performance-Based Award that is a Cash-Based Award. 

 

	SECTION 14.	DIVIDEND EQUIVALENT RIGHTS 

 (a) Dividend Equivalent Rights. The Administrator may
grant Dividend Equivalent Rights under the Plan. A Dividend Equivalent Right is an Award entitling the grantee to receive credits based on cash dividends that would have been paid on the Shares specified in the Dividend Equivalent Right (or other
Award to which it relates) if such Shares had been issued to the grantee. A Dividend Equivalent Right may be granted hereunder to any grantee as a component of an award of Restricted Share Units, Restricted Share Award or Performance Share Award or
as a freestanding award. The terms and conditions of Dividend Equivalent Rights shall be specified in the Award Certificate. Dividend equivalents credited to the holder of a Dividend Equivalent Right may be paid currently or may be deemed to be
reinvested in additional Shares, which may thereafter accrue additional equivalents. Any such reinvestment shall be at Fair Market Value on the date of reinvestment or such other price as may then apply under a dividend reinvestment plan sponsored
by the Company, if any. Dividend Equivalent Rights may be settled in cash or Shares or a combination thereof, in a single installment or installments. A Dividend Equivalent Right granted as a component of an Award of Restricted Share Units or 

 

	3 	 A number approximately equal to $15 million Black-Scholes value. 

  
 14 

 
Performance Share Award shall provide that such Dividend Equivalent Right shall be settled only upon settlement or payment of, or lapse of restrictions on, such other Award, and that such
Dividend Equivalent Right shall expire or be forfeited or annulled under the same conditions as such other Award. 
 (b) Termination.
Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 19 below, in writing after the Award is issued, a grantee’s rights in all Dividend Equivalent Rights shall automatically
terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason. 
  

	SECTION 15.	TRANSFERABILITY OF AWARDS 

 (a) Transferability. Except as provided in
Section 15(b) below, during a grantee’s lifetime, his or her Awards shall be exercisable only by the grantee, or by the grantee’s legal representative or guardian in the event of the grantee’s incapacity. No Awards shall be sold,
assigned, transferred or otherwise encumbered or disposed of by a grantee other than by will or by the laws of descent and distribution or pursuant to a domestic relations order. No Awards shall be subject, in whole or in part, to attachment,
execution, or levy of any kind, and any purported transfer in violation hereof shall be null and void. 
 (b) Administrator Action.
Notwithstanding Section 15(a), the Administrator, in its discretion, may provide either in the Award Certificate regarding a given Award or by subsequent written approval that the grantee (who is an employee or director) may transfer his or her
Non-Qualified Share Options to his or her immediate family members, to trusts for the benefit of such family members, or to partnerships in which such family members are the only partners, provided that the transferee agrees in writing with the
Company to be bound by all of the terms and conditions of this Plan and the applicable Award. In no event may an Award be transferred by a grantee for value. 

(c) Family Member. For purposes of Section 15(b), “family member” shall mean a grantee’s child, stepchild,
grandchild, parent, stepparent, grandparent, spouse, former spouse, sibling, niece, nephew, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, any person sharing the
grantee’s household (other than a tenant of the grantee), a trust in which these persons (or the grantee) have more than 50 percent of the beneficial interest, a foundation in which these persons (or the grantee) control the management of
assets, and any other entity in which these persons (or the grantee) own more than 50 percent of the voting interests. 
 (d) Designation
of Beneficiary. To the extent permitted by the Company, each grantee to whom an Award has been made under the Plan may designate a beneficiary or beneficiaries to exercise any Award or receive any payment under any Award payable on or after the
grantee’s death. Any such designation shall be on a form provided for that purpose by the Administrator and shall not be effective until received by the Administrator. If no beneficiary has been designated by a deceased grantee, or if the
designated beneficiaries have predeceased the grantee, the beneficiary shall be the grantee’s estate. 

  
 15 

	SECTION 16.	TAX WITHHOLDING 

 (a) Payment by Grantee. Each grantee shall, no later than the
date as of which the value of an Award or of any Shares or other amounts received thereunder first becomes includable in the gross income of the grantee for Federal income tax purposes, pay to the Company, or make arrangements satisfactory to the
Administrator regarding payment of, any Federal, state, or local taxes of any kind required by law to be withheld by the Company with respect to such income. The Company and its Subsidiaries shall, to the extent permitted by law, have the right to
deduct any such taxes from any payment of any kind otherwise due to the grantee. The Company’s obligation to deliver evidence of book entry (or share certificates) to any grantee is subject to and conditioned on tax withholding obligations
being satisfied by the grantee. 
 (b) Payment in Shares. Subject to approval by the Administrator, a grantee may elect to have the
Company’s minimum required tax withholding obligation satisfied, in whole or in part, by authorizing the Company to withhold from Shares to be issued pursuant to any Award a number of shares with an aggregate Fair Market Value (as of the date
the withholding is effected) that would satisfy the withholding amount due. The Administrator may also require Awards to be subject to mandatory share withholding up to the required withholding amount. For purposes of share withholding, the Fair
Market Value of withheld shares shall be determined in the same manner as the value of Shares includible in income of the Participants. 
  

	SECTION 17.	SECTION 409A AWARDS 

 To the extent that any Award is determined to constitute
“nonqualified deferred compensation” within the meaning of Section 409A (a “409A Award”), the Award shall be subject to such additional rules and requirements as specified by the Administrator from time to time in order to
comply with Section 409A. In this regard, if any amount under a 409A Award is payable upon a “separation from service” (within the meaning of Section 409A) to a grantee who is then considered a “specified employee”
(within the meaning of Section 409A), then no such payment shall be made prior to the date that is the earlier of (i) six months and one day after the grantee’s separation from service, or (ii) the grantee’s death, but only
to the extent such delay is necessary to prevent such payment from being subject to interest, penalties and/or additional tax imposed pursuant to Section 409A. Further, the settlement of any such Award may not be accelerated except to the
extent permitted by Section 409A. 
  

	SECTION 18.	TERMINATION OF EMPLOYMENT, TRANSFER, LEAVE OF ABSENCE, ETC. 

 (a) Termination of
Employment. If the grantee’s employer ceases to be a Subsidiary, the grantee shall be deemed to have terminated employment for purposes of the Plan. 

(b) For purposes of the Plan, the following events shall not be deemed a termination of employment: 

(i) a transfer to the employment of the Company from a Subsidiary or from the Company to a Subsidiary, or from one Subsidiary to another; or

 (ii) an approved leave of absence for military service or sickness, or for any other purpose approved by the Company, if the
employee’s right to re-employment is guaranteed either by a statute or by contract or under the policy pursuant to which the leave of absence was granted or if the Administrator otherwise so provides in writing. 

  
 16 

	SECTION 19.	AMENDMENTS AND TERMINATION 

 The Board may, at any time, amend or discontinue the Plan
and the Administrator may, at any time, amend or cancel any outstanding Award for the purpose of satisfying changes in law or for any other lawful purpose, but no such action shall adversely affect rights under any outstanding Award without the
holder’s consent. Except as provided in Section 3(b) or 3(c), without prior shareholder approval, in no event may the Administrator exercise its discretion to reduce the exercise price of outstanding Share Options or Share Appreciation
Rights or effect repricing through cancellation and re-grants or cancellation of Share Options or Share Appreciation Rights in exchange for cash or other Awards. To the extent required under the rules of any securities exchange or market system on
which the Shares are listed, to the extent determined by the Administrator to be required by the Code to ensure that Incentive Share Options granted under the Plan are qualified under Section 422 of the Code, or to ensure that compensation
earned under Awards qualifies as performance-based compensation under Section 162(m) of the Code, Plan amendments shall be subject to approval by the Company shareholders entitled to vote at a meeting of shareholders. Nothing in this
Section 19 shall limit the Administrator’s authority to take any action permitted pursuant to Section 3(b) or 3(c). 
  

	SECTION 20.	STATUS OF PLAN 

 With respect to the portion of any Award that has not been exercised and
any payments in cash, Shares or other consideration not received by a grantee, a grantee shall have no rights greater than those of a general creditor of the Company unless the Administrator shall otherwise expressly determine in connection with any
Award or Awards. In its sole discretion, the Administrator may authorize the creation of trusts or other arrangements to meet the Company’s obligations to deliver Shares or make payments with respect to Awards hereunder, provided that the
existence of such trusts or other arrangements is consistent with the foregoing sentence. 
  

	SECTION 21.	GENERAL PROVISIONS 

 (a) No Distribution. The Administrator may require each
person acquiring Shares pursuant to an Award to represent to and agree with the Company in writing that such person is acquiring the shares without a view to distribution thereof. 

(b) Delivery of Share Certificates. Share certificates to grantees under this Plan shall be deemed delivered for all purposes when the
Company or a Share transfer agent of the Company shall have mailed such certificates in the United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company. Uncertificated Shares shall be deemed
delivered for all purposes when the Company or a Share transfer agent of the Company shall have given to the grantee by electronic mail (with proof of receipt) or by United States mail, addressed to the grantee, at the grantee’s last known
address on file with the Company, notice of issuance and recorded the issuance in its records (which may include electronic “book 

  
 17 

 
entry” records). Notwithstanding anything herein to the contrary, the Company shall not be required to issue or deliver any certificates evidencing Shares pursuant to the exercise of any
Award, unless and until the Administrator has determined, with advice of counsel (to the extent the Administrator deems such advice necessary or advisable), that the issuance and delivery of such certificates is in compliance with all applicable
laws, regulations of governmental authorities and, if applicable, the requirements of any exchange on which the Shares are listed, quoted or traded. All Share certificates delivered pursuant to the Plan shall be subject to any stop-transfer orders
and other restrictions as the Administrator deems necessary or advisable to comply with federal, state or foreign jurisdiction, securities or other laws, rules and quotation system on which the Shares are listed, quoted or traded. The Administrator
may place legends on any Share certificate to reference restrictions applicable to the Shares. In addition to the terms and conditions provided herein, the Administrator may require that an individual make such reasonable covenants, agreements, and
representations as the Administrator, in its discretion, deems necessary or advisable in order to comply with any such laws, regulations, or requirements. The Administrator shall have the right to require any individual to comply with any timing or
other restrictions with respect to the settlement or exercise of any Award, including a window-period limitation, as may be imposed in the discretion of the Administrator. 

(c) Shareholder Rights. Until Shares is deemed delivered in accordance with Section 21(b), no right to vote or receive dividends
or any other rights of a shareholder will exist with respect to Shares to be issued in connection with an Award, notwithstanding the exercise of a Share Option or any other action by the grantee with respect to an Award. 

(d) Other Compensation Arrangements; No Employment Rights. Nothing contained in this Plan shall prevent the Board from adopting other
or additional compensation arrangements, including trusts, and such arrangements may be either generally applicable or applicable only in specific cases. The adoption of this Plan and the grant of Awards do not confer upon any employee any right to
continued employment with the Company or any Subsidiary. 
 (e) Trading Policy Restrictions. Option exercises and other Awards under
the Plan shall be subject to the Company’s insider trading policies and procedures, as in effect from time to time. 
 (f) Clawback
Policy. Awards under the Plan shall be subject to the Company’s clawback policy, as in effect from time to time. 
  

	SECTION 22.	EFFECTIVE DATE OF PLAN 

 This Plan shall become effective on the date immediately prior
to the date of the Company’s Initial Public Offering following shareholder approval in accordance with applicable state law, the Company’s bylaws and articles of incorporation, and applicable stock exchange rules or pursuant to written
consent. No grants of Share Options and other Awards may be made hereunder after the tenth anniversary of the Effective Date and no grants of Incentive Share Options may be made hereunder after the tenth anniversary of the date the Plan is approved
by the Board. 

  
 18 

	SECTION 23.	GOVERNING LAW 

 This Plan and all Awards and actions taken thereunder shall be governed
by, and construed in accordance with, the laws of the State of Delaware applied without regard to conflict of law principles. 
 DATE APPROVED BY BOARD OF
DIRECTORS:             , 2015 
 DATE APPROVED BY SHAREHOLDERS:
            , 2015 

  
 19 

 APPENDIX 1 

TERMS AND CONDITIONS APPLICABLE TO AUSTRALIAN PARTICIPANTS 

The Plan is amended as follows in relation to Awards granted to a recipient who is a resident of Australia or is employed in Australia or provides services in
Australia (“Australian Recipient”). 
 Tax deferral. This scheme is a scheme to which Subdivision 83A-C of the Income Tax
Assessment Act 1997 applies (subject to the conditions in that Act). 
 Transferability of Awards. The words “or pursuant to a domestic
relations order” are deleted from Section 15(a) of the Plan for Australian Participants. Section 15(b) of the Plan does not apply to any Australian Participant. 

 Neither this document, nor any Award Certificate connected with it, is an approved prospectus for the purposes
of section 85(1) of the Financial Services and Markets Act 2000 (“FSMA”) and no offer of transferable securities to the public (for the purposes of section 102B of FSMA) is being made in connection with the UK Sub-Plan to the Mimecast
Limited 2015 Share Option and Incentive Plan (the “Sub-Plan”). The Sub-Plan is exclusively available to bona fide employees and former employees of Mimecast Limited and any other UK Subsidiary. 

UK SUB-PLAN TO THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

	SECTION 1.	GENERAL PURPOSE OF THE PLAN; DEFINITIONS 

 The name of the plan is the UK sub-plan to the
Mimecast Limited 2015 Share Option and Incentive Plan (the “Plan”). The purpose of the Plan is to encourage and enable the, employees, of Mimecast Limited (the “Company”) and its Subsidiaries upon whose judgment, initiative and
efforts the Company largely depends for the successful conduct of its business to acquire a proprietary interest in the Company. It is anticipated that providing such persons with a direct stake in the Company’s welfare will assure a closer
identification of their interests with those of the Company and its shareholders, thereby stimulating their efforts on the Company’s behalf and strengthening their desire to remain with the Company. 

The following terms shall be defined as set forth below: 

“Act” means the Securities Act of 1933, as amended, and the rules and regulations thereunder. 

“Administrator” means either the Board or the compensation committee of the Board or a similar committee performing the
functions of the compensation committee and which is comprised of not less than two Non-Employee Directors who are independent. 

“Award” or “Awards,” except where referring to a particular category of grant under the Plan, shall include,
Share Appreciation Rights, Restricted Share Units, Restricted Share Awards, Unrestricted Share Awards, Cash-Based Awards, Performance Share Awards Dividend Equivalent Rights and Unapproved Options. 

“Award Certificate” means a written or electronic document setting forth the terms and provisions applicable to an Award
granted under the Plan. Each Award Certificate is subject to the terms and conditions of the Plan. 
 “Award Tax Liability”
means any liability or obligation of the Company and/or any Subsidiary to account for (or pay) income tax (under the UK withholding system of PAYE (pay 

 
as you earn)) or any other taxation provisions and primary class 1 National Insurance Contributions in the United Kingdom to the extent arising from the grant, exercise, assignment, release,
cancellation, vesting or any other disposal of an Award or arising out of the acquisition, retention and disposal of the Shares acquired under this Plan. 

“Board” means the Board of Directors of the Company. 

“Cash-Based Award” means an Award entitling the recipient to receive a cash-denominated payment. 

“Code” means the Internal Revenue Code of 1986, as amended, and any successor Code, and related rules, regulations and
interpretations. 
 “Covered Employee” means an employee who is a “Covered Employee” within the meaning of
Section 162(m) of the Code. 
 “Dividend Equivalent Right” means an Award entitling the grantee to receive credits
based on cash dividends that would have been paid on the Shares specified in the Dividend Equivalent Right (or other award to which it relates) if such Shares had been issued to and held by the grantee. 

“Effective Date” means the date on which the Plan becomes effective as set forth in Section 21. 

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder. 

“Fair Market Value” of the Shares on any given date means the fair market value of the Shares determined in good faith by the
Administrator; provided, however, that if the Shares are admitted to quotation on the National Association of Securities Dealers Automated Quotation System (“NASDAQ”), NASDAQ Global Market or another national securities exchange, the
determination shall be made by reference to market quotations. If there are no market quotations for such date, the determination shall be made by reference to the last date preceding such date for which there are market quotations; provided
further, however, that if the date for which Fair Market Value is determined is the first day when trading prices for the Shares are reported on a national securities exchange, the Fair Market Value shall be the “Price to the Public” (or
equivalent) set forth on the cover page for the final prospectus relating to the Company’s Initial Public Offering. 
 “Initial
Public Offering” means the first underwritten, firm commitment public offering pursuant to an effective registration statement under the Act covering the offer and sale by the Company of its equity securities, or such other event as a
result of or following which the Shares shall be publicly held. 
 “ITEPA” means the Income Tax (Earnings and Pensions) Act
2003. 

 “Joint Agreement” means an agreement (in accordance with paragraph 3A of
Schedule 1 to the Social Security Contributions and Benefits Act 1992), for the Secondary Contributor to recover any Secondary NIC Liability from the grantee. 

“Joint Election” means an election (in such terms and such form as provided in paragraphs 3A and 3B of Schedule 1 to the
Social Security Contributions and Benefits Act 1992), which has been approved by HM Revenue & Customs for the transfer of the whole of or any liability of the Secondary Contributor for any Secondary NIC Liability. 

“Non-Employee Director” means a member of the Board who is not also an employee of the Company or any Subsidiary. 

“Option” or “Share Option” means any option to purchase Shares granted pursuant to Section 5. 

“Ordinary Shares” means the ordinary shares of the Company. 

“Performance-Based Award” means any Restricted Share Award, Restricted Share Units, Performance Share Award or Cash-Based
Award granted to a Covered Employee that is intended to qualify as “performance-based compensation” under Section 162(m) of the Code and the regulations promulgated thereunder. 

“Personal Representative” means the personal representative(s) of a grantee (being either the executors of his will or if he
dies intestate the duly appointed administrator(s) of his estate) who have provided to the Board evidence of their appointment as such. 

“Performance Criteria” means the criteria that the Administrator selects for purposes of establishing the Performance Goal or Performance
Goals for an individual for a Performance Cycle. The Performance Criteria (which shall be applicable to the organizational level specified by the Administrator, including, but not limited to, the Company or a unit, division, group, or Subsidiary of
the Company) that will be used to establish Performance Goals are limited to the following: total shareholder return; expense levels; cash flow (including, but not limited to, operating cash flow and free cash flow); business development and
financing milestones; earnings before interest, taxes, depreciation and amortization, or any elements thereof; net income (loss) (either before or after interest, taxes, depreciation and/or amortization); changes in the market price of the
Company’s ordinary shares; economic value-added; sales or revenue; acquisitions or strategic transactions; operating income (loss); return on capital, assets, equity, or investment; shareholder returns; return on sales; gross or net profit
levels; productivity; expense; margins; operating efficiency; customer satisfaction; working capital; earnings (loss) per Share; sales or market shares and number of customers; annual spend estimate for new customers signed; number of billable
awards; billings and billings retention rate, any of which may be measured either in absolute terms or as compared to any incremental increase or as compared to results of a peer group. The Committee may appropriately adjust any evaluation
performance under a Performance Criterion to exclude any of the following events that occurs during a Performance Cycle: (i) asset write-downs or impairments, (ii) litigation or claim judgments or settlements, (iii) the effect of
changes in tax law, accounting principles or other such laws or provisions affecting reporting results, (iv) accruals for reorganizations and restructuring 

 
programs, and (v) any item of an unusual nature or of a type that indicates infrequency of occurrence, or both, including those described in the Financial Accounting Standards Board’s
authoritative guidance and/or in management’s discussion and analysis of financial condition of operations appearing the Company’s annual report to shareholders for the applicable year. 

“Performance Cycle” means one or more periods of time, which may be of varying and overlapping durations, as the
Administrator may select, over which the attainment of one or more Performance Criteria will be measured for the purpose of determining a grantee’s right to and the payment of a Restricted Share Award, Restricted Share Units, Performance Share
Award or Cash-Based Award, the vesting and/or payment of which is subject to the attainment of one or more Performance Goals. Each such period shall not be less than 12 months. 

“Performance Goals” means, for a Performance Cycle, the specific goals established in writing by the Administrator for a
Performance Cycle based upon the Performance Criteria.  
 “Performance Share Award” means an Award entitling the
recipient to acquire Shares upon the attainment of specified performance goals. 
 “Restricted Shares” means the Shares
underlying a Restricted Share Award that remain subject to a risk of forfeiture or the Company’s right of repurchase. 

“Restricted Share Award” means an Award of Restricted Shares subject to such restrictions and conditions as the Administrator
may determine at the time of grant. 
 “Restricted Share Units” means an Award of share units subject to such
restrictions and conditions as the Administrator may determine at the time of grant. 
 “Sale Event” means
(i) the sale of all or substantially all of the assets of the Company on a consolidated basis to an unrelated person or entity, (ii) a merger, reorganization or consolidation pursuant to which the holders of the Company’s outstanding
voting power and outstanding shares immediately prior to such transaction do not own a majority of the outstanding voting power and outstanding shares or other equity interests of the resulting or successor entity (or its ultimate parent, if
applicable) immediately upon completion of such transaction, (iii) the sale of all of the Shares of the Company to an unrelated person, entity or group thereof acting in concert, or (iv) any other transaction in which the owners of the
Company’s outstanding voting power immediately prior to such transaction do not own at least a majority of the outstanding voting power of the Company or any successor entity immediately upon completion of the transaction other than as a result
of the acquisition of securities directly from the Company. 
 “Sale Price” means the value as determined by
the Administrator of the consideration payable, or otherwise to be received by shareholders, per Share pursuant to a Sale Event. 

“Section 409A” means Section 409A of the Code and the regulations and other guidance promulgated thereunder. 

“Secondary Contributor” means a person or company who has a liability to account (or pay) the Secondary NIC Liability to HM
Revenue & Customs. 

 “Secondary NIC Liability” means any liability to employer’s Class 1
National Insurance Contributions to the extent arising from the grant, exercise, release, vesting or cancellation of an Award or arising out of the acquisition, retention and disposal of the Shares acquired pursuant to an Award. 

“Section 431 Election” means an election made under section 431 ITEPA. 

“Shares” means the Ordinary Shares, subject to adjustments pursuant to Section 3. 

“Share Appreciation Right” means an Award entitling the recipient to receive Shares having a value equal to the excess of the
Fair Market Value of the Shares on the date of exercise over the exercise price of the Share Appreciation Right multiplied by the number of Shares with respect to which the Share Appreciation Right shall have been exercised. 

“Subsidiary” means any corporation or other entity (other than the Company) in which the Company has at least a 50 percent
interest, either directly or indirectly. 
 “Unapproved Option” means an option over shares in the Company that is
neither an HM Revenue & Customs tax favoured company share option (under Schedule 4 ITEPA) nor an enterprise management incentive (EMI) option under Schedule 5 ITEPA. 

“Unrestricted Share Award” means an Award of Shares free of any restrictions. 

“UK Subsidiary” means a Subsidiary of the Company which is incorporated in the UK. 

“US Plan” means the Mimecast Limited 2015 Share Option and Incentive Plan. 

 

	SECTION 2.	ADMINISTRATION OF PLAN; ADMINISTRATOR AUTHORITY TO SELECT GRANTEES AND DETERMINE AWARDS 

(a) Administration of Plan. The Plan shall be administered by the Administrator. 

(b) Powers of Administrator. The Administrator shall have the power and authority to grant Awards consistent with the terms of the
Plan, including the power and authority: 
 (i) to select the individuals to whom Awards may from time to time be granted; 

(ii) to determine the time or times of grant, and the extent, if any, of Share Appreciation Rights, Restricted Share Awards, Restricted Share
Units, Unrestricted Share Awards, Cash-Based Awards, Performance Share Awards Dividend Equivalent Rights and Unapproved Options, or any combination of the foregoing, granted to any one or more grantees; 

(iii) to determine the number of Shares to be covered by any Award; 

(iv) to determine and modify from time to time the terms and conditions, including restrictions, not inconsistent with the terms of the Plan,
of any Award, which terms and conditions may differ among individual Awards and grantees, and to approve the forms of Award Certificates; 

 (v) to accelerate at any time the exercisability or vesting of all or any portion of any Award;

 (vi) subject to the provisions of Section 5 (c), to extend at any time the period in which Share Options may be exercised; 

(vii) at any time to adopt, alter and repeal such rules, guidelines and practices for administration of the Plan and for its own acts and
proceedings as it shall deem advisable; 
 (viii) to interpret the terms and provisions of the Plan and any Award (including related written
instruments); 
 (ix) to make all determinations it deems advisable for the administration of the Plan; and 

(x) to decide all disputes arising in connection with the Plan; and to otherwise supervise the administration of the Plan. 

All decisions and interpretations of the Administrator shall be binding on all persons, including the Company and Plan grantees. 

(c) Delegation of Authority to Grant Awards. Subject to applicable law, the Administrator, in its discretion, may delegate to the Chief
Executive Officer of the Company all or part of the Administrator’s authority and duties with respect to the granting of Awards to individuals who are (i) not subject to the reporting and other provisions of Section 16 of the Exchange
Act and (ii) not Covered Employees. Any such delegation by the Administrator shall include a limitation as to the number of Shares underlying Awards that may be granted during the period of the delegation and shall contain guidelines as to the
determination of the exercise price and the vesting criteria. The Administrator may revoke or amend the terms of a delegation at any time but such action shall not invalidate any prior actions of the Administrator’s delegate or delegates that
were consistent with the terms of the Plan. 
 (d) Award Certificate. Awards under the Plan shall be evidenced by Award Certificates
that set forth the terms, conditions and limitations for each Award which may include, without limitation, the term of an Award and the provisions applicable in the event employment or service terminates. 

(e) Indemnification. Neither the Board nor the Administrator, nor any member of either or any delegate thereof, shall be liable for any
act, omission, interpretation, construction or determination made in good faith in connection with the Plan, and the members of the Board and the Administrator (and any delegate thereof) shall be entitled in all cases to indemnification and
reimbursement by the Company in respect of any claim, loss, damage or expense (including, without limitation, reasonable attorneys’ fees) arising or resulting therefrom to the fullest extent permitted by law and/or under the Company’s
articles or bylaws or any directors’ and officers’ liability insurance coverage which may be in effect from time to time and/or any indemnification agreement between such individual and the Company. 

	SECTION 3.	SHARES ISSUABLE UNDER THE PLAN; MERGERS; SUBSTITUTION 

 (a) Shares Issuable. The
maximum number of Shares reserved and available for issuance under the US Plan (together with the Plan) shall be [                ]1 Shares (the “Initial Limit”), subject to adjustment as provided in this Section 3, plus on January 1, 2016 and each January 1 thereafter, the number of Shares reserved and
available for issuance under the US Plan (together with the Plan) shall be cumulatively increased by five percent of the number of Shares issued and outstanding on the immediately preceding December 31 or such lesser number of Shares determined
by the Administrator (the “Annual Increase”). The Shares underlying any Awards that are forfeited, canceled, held back upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding, reacquired by the
Company prior to vesting, satisfied without the issuance of Shares or otherwise terminated under the US Plan (together with the Plan) (other than by exercise) shall be added back to the Shares available for issuance under the US Plan (together with
the Plan). In the event the Company repurchases Shares on the open market, such Shares shall not be added to the Shares available for issuance under the US Plan (together with the Plan). Shares may be issued up to the maximum number of Shares
available under the US Plan (together with the Plan) pursuant to any type or types of Award; provided, however, that Share Options or Share Appreciation Rights with respect to no more than
[                ]2 Shares may be granted to any one individual grantee during any one calendar year period. The
Shares available for issuance under the US Plan (together with the Plan) may be authorized but unissued Shares or Shares reacquired by the Company. 

(b) Changes in Shares. Subject to Section 3(c) hereof, if, as a result of any reorganization, recapitalization, reclassification,
share dividend, share split, reverse share split or other similar change in the Company’s share capital, the outstanding Shares are increased or decreased or are exchanged for a different number or kind of shares or other securities of the
Company, or additional shares or new or different shares or other securities of the Company or other non-cash assets are distributed with respect to such Shares or other securities, or, if, as a result of any merger or consolidation, sale of all or
substantially all of the assets of the Company, the outstanding Shares are converted into or exchanged for securities of the Company or any successor entity (or a parent or subsidiary thereof), the Administrator shall make an appropriate or
proportionate adjustment in (i) the maximum number of Shares reserved for issuance under the Plan, (ii) the number of Share Options or Share Appreciation Rights that can be granted to any one individual grantee and the maximum number of
Shares that may be granted under a Performance-Based Award, (iii) the number and kind of Shares or other securities subject to any then outstanding Awards under the Plan, (iv) the repurchase price, if any, per Share subject to each
outstanding Restricted Share Award, and (v) the exercise price for each Share subject to any then outstanding Share Options and Share Appreciation Rights under the Plan, without changing the aggregate exercise price (i.e., the exercise price
multiplied by the number of Share Options and Share Appreciation Rights) as to which such Share Options and Share Appreciation Rights 

 

	1 	A number equal to 10% of the post-IPO outstanding. 

	2 	A number approximately equal to $15 million Black-Scholes value. 

 
remain exercisable. The Administrator shall also make equitable or proportionate adjustments in the number of Shares subject to outstanding Awards and the exercise price and the terms of
outstanding Awards to take into consideration cash dividends paid other than in the ordinary course or any other extraordinary corporate event. The adjustment by the Administrator shall be final, binding and conclusive. No fractional Shares shall be
issued under the Plan resulting from any such adjustment, but the Administrator in its discretion may make a cash payment in lieu of fractional Shares. 

(c) Mergers and Other Transactions. In the case of and subject to the consummation of a Sale Event, the parties thereto may cause the
assumption or continuation of Awards theretofore granted by the successor entity, or the substitution of such Awards with new Awards of the successor entity or parent thereof, with appropriate adjustment as to the number and kind of shares and, if
appropriate, the per Share exercise prices, as such parties shall agree. To the extent the parties to such Sale Event do not provide for the assumption, continuation or substitution of Awards, upon the effective time of the Sale Event, the Plan and
all outstanding Awards granted hereunder shall terminate. In such case, except as may be otherwise provided in the relevant Award Certificate, all Options and Share Appreciation Rights that are not exercisable immediately prior to the effective time
of the Sale Event shall become fully exercisable as of the effective time of the Sale Event, all other Awards with time-based vesting, conditions or restrictions shall become fully vested and nonforfeitable as of the effective time of the Sale
Event, and all Awards with conditions and restrictions relating to the attainment of performance goals may become vested and nonforfeitable in connection with a Sale Event in the Administrator’s discretion or to the extent specified in the
relevant Award Certificate. In the event of such termination, (i) the Company shall have the option (in its sole discretion) to make or provide for a cash payment to the grantees holding Options and Share Appreciation Rights, in exchange for
the cancellation thereof, in an amount equal to the difference between (A) the Sale Price multiplied by the number of Shares subject to outstanding Options and Share Appreciation Rights (to the extent then exercisable at prices not in excess of
the Sale Price) and (B) the aggregate exercise price of all such outstanding Options and Share Appreciation Rights; or (ii) each grantee shall be permitted, within a specified period of time prior to the consummation of the Sale Event as
determined by the Administrator, to exercise all outstanding Options and Share Appreciation Rights (to the extent then exercisable) held by such grantee. 
  

	SECTION 4.	ELIGIBILITY 

 Grantees under the Plan will be employees, of the Company and its
Subsidiaries as are selected from time to time by the Administrator in its sole discretion. 
  

	SECTION 5.	SHARE OPTIONS 

 (a) Award of Share Options. The Administrator may grant Share
Options under the Plan. Any Share Option granted under the Plan shall be in such form as the Administrator may from time to time approve. 

Share Options granted under the Plan will be Unapproved Options. 

 Share Options granted pursuant to this Section 5 shall be subject to the following terms and
conditions and shall contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Administrator shall deem desirable. If the Administrator so determines, Share Options may be granted in lieu of cash compensation
at the optionee’s election, subject to such terms and conditions as the Administrator may establish. 
 (b) Exercise Price. The
exercise price per share for the Shares covered by a Share Option granted pursuant to this Section 5 shall be determined by the Administrator at the time of grant but shall not be less than 100 percent of the Fair Market Value on the date of
grant 
 (c) Option Term. The term of each Share Option shall be fixed by the Administrator, but no Share Option shall be exercisable
more than ten years after the date the Share Option is granted. 
 (d) Exercisability; Rights of a Shareholder. Share Options shall
become exercisable at such time or times, whether or not in installments, as shall be determined by the Administrator at or after the grant date. The Administrator may at any time accelerate the exercisability of all or any portion of any Share
Option. An optionee shall have the rights of a shareholder only as to shares acquired upon the exercise of a Share Option and not as to unexercised Share Options. 

(e) Method of Exercise. Share Options may be exercised in whole or in part, by giving written or electronic notice of exercise to the
Company, specifying the number of Shares to be purchased. Payment of the purchase price may be made by one or more of the following methods: 

(i) In cash, by certified or bank cheque or other instrument acceptable to the Administrator; 

(ii) By the optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to
promptly deliver to the Company cash or a cheque payable and acceptable to the Company for the purchase price; provided that in the event the optionee chooses to pay the purchase price as so provided, the optionee and the broker shall comply with
such procedures and enter into such agreements of indemnity and other agreements as the Company shall prescribe as a condition of such payment procedure; or 

(iii) By a “net exercise” arrangement pursuant to which the Company will reduce the number of Shares issuable upon exercise by the
largest whole number of Shares with a Fair Market Value that does not exceed the aggregate exercise price. 
 Payment instruments will be received subject
to collection. The transfer to the optionee on the records of the Company or of the transfer agent of the Shares to be purchased pursuant to the exercise of a Share Option will be contingent upon receipt from the optionee (or a purchaser acting in
his stead in accordance with the provisions of the Share Option) by the Company of the full purchase price for such shares and the fulfillment of any other requirements contained in the Option Award Certificate or applicable provisions of laws
(including the satisfaction of any withholding taxes that the Company is obligated to withhold with respect to the optionee). In the event that the Company establishes, for itself or using the services of a third party, an automated system for the
exercise of Share Options, such as a system using an internet website or interactive voice response, then the paperless exercise of Share Options may be permitted through the use of such an automated system. 

	SECTION 6.	SHARE APPRECIATION RIGHTS 

 (a) Award of Share Appreciation Rights. The
Administrator may grant Share Appreciation Rights under the Plan. A Share Appreciation Right is an Award entitling the recipient to receive Shares having a value equal to the excess of the Fair Market Value of a Share on the date of exercise over
the exercise price of the Share Appreciation Right multiplied by the number of Shares with respect to which the Share Appreciation Right shall have been exercised. 

(b) Exercise Price of Share Appreciation Rights. The exercise price of a Share Appreciation Right shall not be less than 100 percent of
the Fair Market Value of the Shares on the date of grant. 
 (c) Grant and Exercise of Share Appreciation Rights. Share Appreciation
Rights may be granted by the Administrator independently of any Share Option granted pursuant to Section 6 of the Plan. 
 (d) Terms
and Conditions of Share Appreciation Rights. Share Appreciation Rights shall be subject to such terms and conditions as shall be determined from time to time by the Administrator. The term of a Share Appreciation Right may not exceed ten years.

  

	SECTION 7.	RESTRICTED SHARE AWARDS 

 (a) Nature of Restricted Share Awards. The Administrator
may grant Restricted Share Awards under the Plan. A Restricted Share Award is any Award of Restricted Shares subject to such restrictions and conditions as the Administrator may determine at the time of grant. Conditions may be based on continuing
employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among
individual Awards and grantees. 
 (b) Rights as a Shareholder. Upon the grant of the Restricted Share Award and payment of any
applicable purchase price, a grantee shall have the rights of a shareholder with respect to the voting of the Restricted Shares and receipt of dividends; provided that if the lapse of restrictions with respect to the Restricted Share Award is tied
to the attainment of performance goals, any dividends paid by the Company during the performance period shall accrue and shall not be paid to the grantee until and to the extent the performance goals are met with respect to the Restricted Share
Award. Unless the Administrator shall otherwise determine, (i) uncertificated Restricted Shares shall be accompanied by a notation on the records of the Company or the transfer agent to the effect that they are subject to forfeiture until such
Restricted Shares are vested as provided in Section 7(d) below, and (ii) certificated Restricted Shares shall remain in the possession of the Company until such Restricted Shares are vested as provided in Section 7(d) below, and the
grantee shall be required, as a condition of the grant, to deliver to the Company such instruments of transfer as the Administrator may prescribe. 

 (c) Restrictions. Restricted Shares may not be sold, assigned, transferred, pledged or
otherwise encumbered or disposed of except as specifically provided herein or in the Restricted Share Award Certificate. Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 18 below,
in writing after the Award is issued, if a grantee’s employment (or other service relationship) with the Company and its Subsidiaries terminates for any reason, any Restricted Shares that have not vested at the time of termination shall
automatically and without any requirement of notice to such grantee from or other action by or on behalf of, the Company be deemed to have been reacquired by the Company at its original purchase price (if any) from such grantee or such
grantee’s legal representative simultaneously with such termination of employment (or other service relationship), and thereafter shall cease to represent any ownership of the Company by the grantee or rights of the grantee as a shareholder.
Following such deemed reacquisition of Restricted Shares that are represented by physical certificates, a grantee shall surrender such certificates to the Company upon request without consideration. 

(d) Vesting of Restricted Shares. The Administrator at the time of grant shall specify the date or dates and/or the attainment of
pre-established performance goals, objectives and other conditions on which the non-transferability of the Restricted Shares and the Company’s right of repurchase or forfeiture shall lapse. Subsequent to such date or dates and/or the attainment
of such pre-established performance goals, objectives and other conditions, the shares on which all restrictions have lapsed shall no longer be Restricted Shares and shall be deemed “vested.” 

Specific UK Securities laws advice must be taken where Restricted Shares are acquired by grantees. Awards of Restricted Shares will not
be made except in consultation with UK counsel. 
  

	SECTION 8.	RESTRICTED SHARE UNITS 

 (a) Nature of Restricted Share Units. The Administrator
may grant Restricted Share Units under the Plan. A Restricted Share Unit is an Award of share units that may be settled in Shares upon the satisfaction of such restrictions and conditions at the time of grant. Conditions may be based on continuing
employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among
individual Awards and grantees. Except in the case of Restricted Share Units with a deferred settlement date that complies with Section 409A, at the end of the vesting period, the Restricted Share Units, to the extent vested, shall be settled
in the form of Shares. Restricted Share Units with deferred settlement dates are subject to Section 409A and shall contain such additional terms and conditions as the Administrator shall determine in its sole discretion in order to comply with
the requirements of Section 409A. 
 (b) Election to Receive Restricted Share Units in Lieu of Compensation. The Administrator
may, in its sole discretion, permit a grantee to elect to receive a portion of future cash compensation otherwise due to such grantee in the form of an award of Restricted Share Units. Any such election shall be made in writing and shall be
delivered to the Company no later than the date specified by the Administrator and in accordance with Section 409A and such other rules and procedures established by the Administrator. Any such future cash compensation that

 
the grantee elects to defer shall be converted to a fixed number of Restricted Share Units based on the Fair Market Value of the Shares on the date the compensation would otherwise have been paid
to the grantee if such payment had not been deferred as provided herein. The Administrator shall have the sole right to determine whether and under what circumstances to permit such elections and to impose such limitations and other terms and
conditions thereon as the Administrator deems appropriate. Any Restricted Share Units that are elected to be received in lieu of cash compensation shall be fully vested, unless otherwise provided in the Award Certificate. 

(c) Rights as a Shareholder. A grantee shall have the rights as a shareholder only as to Shares acquired by the grantee upon settlement
of Restricted Share Units; provided, however, that the grantee may be credited with Dividend Equivalent Rights with respect to the share units underlying his Restricted Share Units, subject to the provisions of Section 13 and such terms and
conditions as the Administrator may determine. 
 (d) Termination. Except as may otherwise be provided by the Administrator either in
the Award Certificate or, subject to Section 18 below, in writing after the Award is issued, a grantee’s right in all Restricted Share Units that have not vested shall automatically terminate upon the grantee’s termination of
employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason. 
  

	SECTION 9.	UNRESTRICTED SHARE AWARDS 

 Grant or Sale of Unrestricted Shares. The
Administrator may grant (or sell at par value or such higher purchase price determined by the Administrator) an Unrestricted Share Award under the Plan. An Unrestricted Share Award is an Award pursuant to which the grantee may receive Shares free of
any restrictions under the Plan. Unrestricted Share Awards may be granted in respect of past services or other valid consideration, or in lieu of cash compensation due to such grantee. 

Specific UK Securities laws advice must be taken where Unrestricted Share Awards are granted. Awards of Unrestricted Shares will not be
made except in consultation with UK counsel. 
  

	SECTION 10.	CASH-BASED AWARDS 

 Grant of Cash-Based Awards. The Administrator may grant
Cash-Based Awards under the Plan. A Cash-Based Award is an Award that entitles the grantee to a payment in cash upon the attainment of specified Performance Goals. The Administrator shall determine the maximum duration of the Cash-Based Award, the
amount of cash to which the Cash-Based Award pertains, the conditions upon which the Cash-Based Award shall become vested or payable, and such other provisions as the Administrator shall determine. Each Cash-Based Award shall specify a
cash-denominated payment amount, formula or payment ranges as determined by the Administrator. Payment, if any, with respect to a Cash-Based Award shall be made in accordance with the terms of the Award and may be made in cash. 

	SECTION 11.	PERFORMANCE SHARE AWARDS 

 (a) Nature of Performance Share Awards. The
Administrator may grant Performance Share Awards under the Plan. A Performance Share Award is an Award entitling the grantee to receive Shares upon the attainment of performance goals. The Administrator shall determine whether and to whom
Performance Share Awards shall be granted, the performance goals, the periods during which performance is to be measured, which may not be less than one year except in the case of a Sale Event, and such other limitations and conditions as the
Administrator shall determine. 
 (b) Rights as a Shareholder. A grantee receiving a Performance Share Award shall have the rights of
a shareholder only as to Shares actually received by the grantee under the Plan and not with respect to Shares subject to the Award but not actually received by the grantee. A grantee shall be entitled to receive Shares under a Performance Share
Award only upon satisfaction of all conditions specified in the Performance Share Award Certificate (or in a performance plan adopted by the Administrator). 

(c) Termination. Except as may otherwise be provided by the Administrator either in the Award agreement or, subject to Section 18
below, in writing after the Award is issued, a grantee’s rights in all Performance Share Awards shall automatically terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its
Subsidiaries for any reason. 
  

	SECTION 12.	PERFORMANCE-BASED AWARDS TO COVERED EMPLOYEES 

 (a) Performance-Based Awards. The
Administrator may grant one or more Performance-Based Awards in the form of a Restricted Share Award, Restricted Share Units, Performance Share Awards or Cash-Based Award payable upon the attainment of Performance Goals that are established by the
Administrator and relate to one or more of the Performance Criteria, in each case on a specified date or dates or over any period or periods determined by the Administrator. The Administrator shall define in an objective fashion the manner of
calculating the Performance Criteria it selects to use for any Performance Cycle. Depending on the Performance Criteria used to establish such Performance Goals, the Performance Goals may be expressed in terms of overall Company performance or the
performance of a division, business unit, or an individual. Each Performance-Based Award shall comply with the provisions set forth below. 

(b) Grant of Performance-Based Awards. With respect to each Performance-Based Award granted to a Covered Employee, the Administrator
shall select, within the first 90 days of a Performance Cycle (or, if shorter, within the maximum period allowed under Section 162(m) of the Code) the Performance Criteria for such grant, and the Performance Goals with respect to each
Performance Criterion (including a threshold level of performance below which no amount will become payable with respect to such Award). Each Performance-Based Award will specify the amount payable, or the formula for determining the amount payable,
upon achievement of the various applicable performance targets. The Performance Criteria established by the Administrator may be (but need not be) different for each Performance Cycle and different Performance Goals may be applicable to
Performance-Based Awards to different Covered Employees. 

 (c) Payment of Performance-Based Awards. Following the completion of a Performance Cycle,
the Administrator shall meet to review and certify in writing whether, and to what extent, the Performance Goals for the Performance Cycle have been achieved and, if so, to also calculate and certify in writing the amount of the Performance-Based
Awards earned for the Performance Cycle. The Administrator shall then determine the actual size of each Covered Employee’s Performance-Based Award. 

(d) Maximum Award Payable. The maximum Performance-Based Award payable to any one Covered Employee under the Plan for a Performance
Cycle is [                ]3 Shares (subject to adjustment as provided in Section 3(b) hereof) or $15,000,000
in the case of a Performance-Based Award that is a Cash-Based Award. 
  

	SECTION 13.	DIVIDEND EQUIVALENT RIGHTS 

 (a) Dividend Equivalent Rights. The Administrator may
grant Dividend Equivalent Rights under the Plan. A Dividend Equivalent Right is an Award entitling the grantee to receive credits based on cash dividends that would have been paid on the Shares specified in the Dividend Equivalent Right (or other
Award to which it relates) if such Shares had been issued to the grantee. A Dividend Equivalent Right may be granted hereunder to any grantee as a component of an award of Restricted Share Units, Restricted Share Award or Performance Share Award or
as a freestanding award. The terms and conditions of Dividend Equivalent Rights shall be specified in the Award Certificate. Dividend equivalents credited to the holder of a Dividend Equivalent Right may be paid currently or may be deemed to be
reinvested in additional Shares, which may thereafter accrue additional equivalents. Any such reinvestment shall be at Fair Market Value on the date of reinvestment or such other price as may then apply under a dividend reinvestment plan sponsored
by the Company, if any. Dividend Equivalent Rights may be settled in cash or Shares or a combination thereof, in a single installment or installments. A Dividend Equivalent Right granted as a component of an Award of Restricted Share Units or
Performance Share Award shall provide that such Dividend Equivalent Right shall be settled only upon settlement or payment of, or lapse of restrictions on, such other Award, and that such Dividend Equivalent Right shall expire or be forfeited or
annulled under the same conditions as such other Award. 
 (b) Termination. Except as may otherwise be provided by the Administrator
either in the Award Certificate or, subject to Section 18 below, in writing after the Award is issued, a grantee’s rights in all Dividend Equivalent Rights shall automatically terminate upon the grantee’s termination of employment (or
cessation of service relationship) with the Company and its Subsidiaries for any reason. 
  

	3 	A number approximately equal to $15 million Black-Scholes value. 

	SECTION 14.	TRANSFERABILITY OF AWARDS 

 (a) Transferability. During a grantee’s lifetime,
his or her Awards shall be exercisable only by the grantee. No Awards shall be sold, assigned, transferred or otherwise encumbered or disposed of by a grantee other than on death to the grantee’s Personal Representative. No Awards shall be
subject, in whole or in part, to attachment, execution, or levy of any kind, and any purported transfer in violation hereof shall be null and void. 
  

	SECTION 15.	TAX MATTERS 

 (a) In the event that the Company or any Subsidiary determines that it is
required to account to HM Revenue & Customs for any Award Tax Liability or Secondary NIC Liability arising from the grant, exercise, assignment, release, cancellation, vesting or any other disposal of an Award or arising out of the
acquisition, retention and disposal of the Shares acquired pursuant to an Award, the grantee, as a condition to the issue of Shares in connection with an Award, or on the grant, assignment, release or cancellation of an Award, shall make such
arrangements satisfactory to the Company to enable it or any Subsidiary to satisfy any requirement to account for any Award Tax Liability (and, if applicable, any Secondary NIC Liability) that may arise in connection with the Award including, but
not limited to, arrangements satisfactory to the Company for withholding Shares that would otherwise be issued to the grantee. 
 (b) The
grantee may be required to sign a Section 431 Election in relation to Shares issued pursuant to an Award in such form as may be determined by HM Revenue & Customs from time to time. 

(c) The grantee may also be required to sign a Joint Agreement or a Joint Election in respect of the Secondary NIC Liability arising on an
Award. 
  

	SECTION 16.	SECTION 409A AWARDS 

 To the extent that any Award is determined to constitute
“nonqualified deferred compensation” within the meaning of Section 409A (a “409A Award”), the Award shall be subject to such additional rules and requirements as specified by the Administrator from time to time in order to
comply with Section 409A. In this regard, if any amount under a 409A Award is payable upon a “separation from service” (within the meaning of Section 409A) to a grantee who is then considered a “specified employee”
(within the meaning of Section 409A), then no such payment shall be made prior to the date that is the earlier of (i) six months and one day after the grantee’s separation from service, or (ii) the grantee’s death, but only
to the extent such delay is necessary to prevent such payment from being subject to interest, penalties and/or additional tax imposed pursuant to Section 409A. Further, the settlement of any such Award may not be accelerated except to the
extent permitted by Section 409A. 
  

	SECTION 17.	TERMINATION OF EMPLOYMENT, TRANSFER, LEAVE OF ABSENCE, ETC. 

 (a) Termination of
Employment. If the grantee’s employer ceases to be a Subsidiary, the grantee shall be deemed to have terminated employment for purposes of the Plan. 

 (b) For purposes of the Plan, the following events shall not be deemed a termination of
employment: 
 (i) a transfer to the employment of the Company from a Subsidiary or from the Company to a Subsidiary, or from one Subsidiary
to another; or 
 (ii) an approved leave of absence for military service or sickness, or for any other purpose approved by the Company, if
the employee’s right to re-employment is guaranteed either by a statute or by contract or under the policy pursuant to which the leave of absence was granted or if the Administrator otherwise so provides in writing. 

 

	SECTION 18.	AMENDMENTS AND TERMINATION 

 The Board may, at any time, amend or discontinue the Plan
and the Administrator may, at any time, amend or cancel any outstanding Award for the purpose of satisfying changes in law or for any other lawful purpose, but no such action shall adversely affect rights under any outstanding Award without the
holder’s consent. Except as provided in Section 3(b) or 3(c), without prior shareholder approval, in no event may the Administrator exercise its discretion to reduce the exercise price of outstanding Share Options or Share Appreciation
Rights or effect repricing through cancellation and re-grants or cancellation of Share Options or Share Appreciation Rights in exchange for cash or other Awards. To the extent required under the rules of any securities exchange or market system on
which the Shares are listed, or to ensure that compensation earned under Awards qualifies as performance-based compensation under Section 162(m) of the Code, Plan amendments shall be subject to approval by the Company shareholders entitled to
vote at a meeting of shareholders. Nothing in this Section 18 shall limit the Administrator’s authority to take any action permitted pursuant to Section 3(b) or 3(c). 

 

	SECTION 19.	STATUS OF PLAN 

 With respect to the portion of any Award that has not been exercised and
any payments in cash, Shares or other consideration not received by a grantee, a grantee shall have no rights greater than those of a general creditor of the Company unless the Administrator shall otherwise expressly determine in connection with any
Award or Awards. In its sole discretion, the Administrator may authorize the creation of trusts or other arrangements to meet the Company’s obligations to deliver Shares or make payments with respect to Awards hereunder, provided that the
existence of such trusts or other arrangements is consistent with the foregoing sentence. 
  

	SECTION 20.	GENERAL PROVISIONS 

 (a) No Distribution. The Administrator may require each
person acquiring Shares pursuant to an Award to represent to and agree with the Company in writing that such person is acquiring the shares without a view to distribution thereof. 

(b) Delivery of Share Certificates. Share certificates to grantees under this Plan shall be deemed delivered for all purposes when the
Company or a Share transfer agent of the Company shall have mailed such certificates in the United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company. Uncertificated Shares shall be deemed
delivered for all purposes when the Company or a Share transfer agent of the Company 

 
shall have given to the grantee by electronic mail (with proof of receipt) or by United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company,
notice of issuance and recorded the issuance in its records (which may include electronic “book entry” records). Notwithstanding anything herein to the contrary, the Company shall not be required to issue or deliver any certificates
evidencing Shares pursuant to the exercise of any Award, unless and until the Administrator has determined, with advice of counsel (to the extent the Administrator deems such advice necessary or advisable), that the issuance and delivery of such
certificates is in compliance with all applicable laws, regulations of governmental authorities and, if applicable, the requirements of any exchange on which the Shares are listed, quoted or traded. All Share certificates delivered pursuant to the
Plan shall be subject to any stop-transfer orders and other restrictions as the Administrator deems necessary or advisable to comply with federal, state or foreign jurisdiction, securities or other laws, rules and quotation system on which the
Shares are listed, quoted or traded. The Administrator may place legends on any Share certificate to reference restrictions applicable to the Shares. In addition to the terms and conditions provided herein, the Administrator may require that an
individual make such reasonable covenants, agreements, and representations as the Administrator, in its discretion, deems necessary or advisable in order to comply with any such laws, regulations, or requirements. The Administrator shall have the
right to require any individual to comply with any timing or other restrictions with respect to the settlement or exercise of any Award, including a window-period limitation, as may be imposed in the discretion of the Administrator. 

(c) Shareholder Rights. Until Shares is deemed delivered in accordance with Section 20(b), no right to vote or receive dividends
or any other rights of a shareholder will exist with respect to Shares to be issued in connection with an Award, notwithstanding the exercise of a Share Option or any other action by the grantee with respect to an Award. 

(d) Other Compensation Arrangements; No Employment Rights. Nothing contained in this Plan shall prevent the Board from adopting other
or additional compensation arrangements, including trusts, and such arrangements may be either generally applicable or applicable only in specific cases. The adoption of this Plan and the grant of Awards do not confer upon any employee any right to
continued employment with the Company or any Subsidiary. 
 (e) Trading Policy Restrictions. Option exercises and other Awards under
the Plan shall be subject to the Company’s insider trading policies and procedures, as in effect from time to time. 
 (f) Clawback
Policy. Awards under the Plan shall be subject to the Company’s clawback policy, as in effect from time to time. 
  

	SECTION 21.	EFFECTIVE DATE OF PLAN 

 This Plan shall become effective on the date immediately prior
to the date of the Company’s Initial Public Offering following shareholder approval in accordance with applicable state law, the Company’s bylaws and articles of incorporation, and applicable stock exchange rules or pursuant to written
consent. No grants of Share Options and other Awards may be made hereunder after the tenth anniversary of the Effective Date. 

	SECTION 22.	GOVERNING LAW 

 This Plan and all Awards and actions taken thereunder shall be governed
by, and construed in accordance with, the laws of the State of Delaware applied without regard to conflict of law principles. Any Joint Agreement, Joint Election and Section 431 Election shall be governed by the laws of England and Wales. 

DATE APPROVED BY BOARD OF DIRECTORS:             , 2015 

DATE APPROVED BY SHAREHOLDERS:             , 2015 

 INCENTIVE SHARE OPTION AGREEMENT 

UNDER THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

									
	Name of Optionee:	 	     
	 	
				
	No. of Option Shares:	 	  
	 		 	
					
	Option Exercise Price per Share:	 	$	 	  
	 		 	
				
	Grant Date:	 	  
	 		 	
				
	Expiration Date:	 	  
	 		 	

 Pursuant to the Mimecast Limited 2015 Share Option and Incentive Plan as amended through the date hereof (the
“Plan”), Mimecast Limited (the “Company”) hereby grants to the Optionee named above an option (the “Share Option”) to purchase on or prior to the Expiration Date specified above all or part of the number of Ordinary
Shares of the Company (the “Shares”) specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth herein and in the Plan. 

1. Exercisability Schedule. No portion of this Share Option may be exercised until such portion shall have become exercisable. Except
as set forth below, and subject to the discretion of the Administrator (as defined in Section 2 of the Plan) to accelerate the exercisability schedule hereunder, this Share Option shall be exercisable with respect to the following number of
Option Shares on the dates indicated so long as the Optionee remains an employee of the Company or a Subsidiary on such dates: 
  

					
	Incremental Number of
Option Shares Exercisable*	 	 	Exercisability Date
		
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	

  

	*	Max. of $100,000 per yr. 

 Once exercisable, this Share Option shall continue to be exercisable
at any time or times prior to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan. 

 2. Manner of Exercise. 

(a) The Optionee may exercise this Share Option only in the following manner: from time to time on or prior to the Expiration Date of this
Share Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be
purchased. 
 Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by
certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of Shares that have been purchased by the Optionee on the open market or that are beneficially owned by the
Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; or (iii) by the Optionee delivering to the Company a properly executed exercise
notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to pay the option
purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment procedure; or
(iv) a combination of (i), (ii) and (iii) above. Payment instruments will be received subject to collection. 
 The transfer
to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above,
(ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and (iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require
to satisfy itself that the issuance of Shares to be purchased Shares will be in compliance with applicable laws and regulations. In the event the Optionee chooses to pay the purchase price by previously-owned Shares through the attestation method,
the number of Shares transferred to the Optionee upon the exercise of the Share Option shall be net of the Shares attested to. 
 (b) The
Shares purchased upon exercise of this Share Option shall be transferred to the Optionee on the records of the Company or of the transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or
regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder
of, or to have any of the rights of a holder with respect to, any Shares subject to this Share Option unless and until this Share Option shall have been exercised pursuant to the terms hereof, the Company or the transfer agent shall have transferred
the shares to the Optionee, and the Optionee’s name shall have been entered as the shareholder of record on the books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership rights with respect to such
Shares. 
 (c) The minimum number of Shares with respect to which this Share Option may be exercised at any one time shall be 100 Shares,
unless the number of Shares with respect to which this Share Option is being exercised is the total number of shares subject to exercise under this Share Option at the time. 

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Share Option shall be exercisable after the Expiration Date
hereof. 

  
 2 

 3. Termination of Employment. If the Optionee’s employment by the Company or a
Subsidiary (as defined in the Plan) is terminated, the period within which to exercise the Share Option may be subject to earlier termination as set forth below. 

(a) Termination Due to Death. If the Optionee’s employment terminates by reason of the Optionee’s death, any portion of this
Share Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be exercised by the Optionee’s legal representative or legatee for a period of 12 months from the date of death or until the Expiration Date,
if earlier. Any portion of this Share Option that is not exercisable on the date of death shall terminate immediately and be of no further force or effect. 

(b) Termination Due to Disability. If the Optionee’s employment terminates by reason of the Optionee’s disability (as
determined by the Administrator), any portion of this Share Option outstanding on such date, to the extent exercisable on the date of such termination of employment, may thereafter be exercised by the Optionee for a period of 12 months from the date
of disability or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date of disability shall terminate immediately and be of no further force or effect. 

(c) Termination for Cause. If the Optionee’s employment terminates for Cause, any portion of this Share Option outstanding on such
date shall terminate immediately and be of no further force and effect. For purposes hereof, “Cause” shall mean, unless otherwise provided in an employment agreement between the Company and the Optionee, a determination by the
Administrator that the Optionee shall be dismissed as a result of (i) any material breach by the Optionee of any agreement between the Optionee and the Company; (ii) the conviction of, indictment for or plea of nolo contendere by the
Optionee to a felony or a crime involving moral turpitude; or (iii) any material misconduct or willful and deliberate non-performance (other than by reason of disability) by the Optionee of the Optionee’s duties to the Company. 

(d) Other Termination. If the Optionee’s employment terminates for any reason other than the Optionee’s death, the
Optionee’s disability, or Cause, and unless otherwise determined by the Administrator, any portion of this Share Option outstanding on such date may be exercised, to the extent exercisable on the date of termination, for a period of three
months from the date of termination or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date of termination shall terminate immediately and be of no further force or effect. 

The Administrator’s determination of the reason for termination of the Optionee’s employment shall be conclusive and binding on the
Optionee and his or her representatives or legatees. 

  
 3 

 4. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Share
Option shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the
Plan, unless a different meaning is specified herein. 
 5. Transferability. This Agreement is personal to the Optionee, is
non-assignable and is not transferable in any manner, by operation of law or otherwise, other than by will or the laws of descent and distribution. This Share Option is exercisable, during the Optionee’s lifetime, only by the Optionee, and
thereafter, only by the Optionee’s legal representative or legatee. 
 6. Status of the Share Option. This Share Option is
intended to qualify as an “incentive stock option” under Section 422 of the Internal Revenue Code of 1986, as amended (the “Code”), but the Company does not represent or warrant that this Share Option qualifies as such. The
Optionee should consult with his or her own tax advisors regarding the tax effects of this Share Option and the requirements necessary to obtain favorable income tax treatment under Section 422 of the Code, including, but not limited to,
holding period requirements. To the extent any portion of this Share Option does not so qualify as an “incentive stock option,” such portion shall be deemed to be a non-qualified share option. If the Optionee intends to dispose or does
dispose (whether by sale, gift, transfer or otherwise) of any Option Shares within the one-year period beginning on the date after the transfer of such shares to him or her, or within the two-year period beginning on the day after the grant of this
Share Option, he or she will so notify the Company within 30 days after such disposition. 
 7. Tax Withholding. The Optionee shall,
not later than the date as of which the exercise of this Share Option becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local
taxes required by law to be withheld on account of such taxable event. The Company shall have the authority to cause the minimum required tax withholding obligation to be satisfied, in whole or in part, by withholding from Shares to be issued to the
Optionee a number of Shares with an aggregate Fair Market Value that would satisfy the minimum withholding amount due. 
 8. No
Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Optionee in employment and neither the Plan nor this Agreement shall interfere in any way with
the right of the Company or any Subsidiary to terminate the employment of the Optionee at any time. 
 9. Integration. This Agreement
constitutes the entire agreement between the parties with respect to this Share Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 

10. Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the
Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number,

  
 4 

 
home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant
Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Optionee may
have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the
Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law. 

11. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or
delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

			
	MIMECAST LIMITED
		
	 By:
	 	  

		 	 Title:

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable. 
  

							
	Dated:	 	  
	 		 	  

		 		 		 	Optionee’s Signature
				
		 		 		 	Optionee’s name and address:
				
		 		 		 	  

				
		 		 		 	  

				
		 		 		 	  

  
 5 

 NON-QUALIFIED SHARE OPTION AGREEMENT 

FOR COMPANY EMPLOYEES 

UNDER THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

									
	Name of Optionee:	 	     
	 	
				
	No. of Option Shares:	 	  
	 		 	
					
	Option Exercise Price per Share:	 	$	 	  
	 		 	
				
	Grant Date:	 	  
	 		 	
				
	Expiration Date:	 	  
	 		 	

 Pursuant to the Mimecast Limited 2015 Share Option and Incentive Plan as amended through the date hereof (the
“Plan”), Mimecast Limited (the “Company”) hereby grants to the Optionee named above an option (the “Share Option”) to purchase on or prior to the Expiration Date specified above all or part of the number of Ordinary
Shares of the Company (the “Shares”) specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth herein and in the Plan. This Share Option is not intended to be an “incentive
stock option” under Section 422 of the Internal Revenue Code of 1986, as amended. 
 1. Exercisability Schedule. No portion
of this Share Option may be exercised until such portion shall have become exercisable. Except as set forth below, and subject to the discretion of the Administrator (as defined in Section 2 of the Plan) to accelerate the exercisability
schedule hereunder, this Share Option shall be exercisable with respect to the following number of Option Shares on the dates indicated so long as Optionee remains an employee of the Company or a Subsidiary on such dates: 

 

							
	Incremental Number of
Option Shares Exercisable	 	 	Exercisability Date	 
		
	 	                 (    	%) 	 			
	 	                 (    	%) 	 			
	 	                 (    	%) 	 			
	 	                 (    	%) 	 			
	 	                 (    	%) 	 	 	                    	  

 Once exercisable, this Share Option shall continue to be exercisable at any time or times prior to the close
of business on the Expiration Date, subject to the provisions hereof and of the Plan. 

 2. Manner of Exercise. 

(a) The Optionee may exercise this Share Option only in the following manner: from time to time on or prior to the Expiration Date of this
Share Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be
purchased. 
 Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by
certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of Shares that have been purchased by the Optionee on the open market or that are beneficially owned by the
Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; (iii) by the Optionee delivering to the Company a properly executed exercise
notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to pay the option
purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment procedure; (iv) by
a “net exercise” arrangement pursuant to which the Company will reduce the number of Shares issuable upon exercise by the largest whole number of Shares with a Fair Market Value that does not exceed the aggregate exercise price; or
(v) a combination of (i), (ii), (iii) and (iv) above. Payment instruments will be received subject to collection. 
 The
transfer to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above,
(ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and (iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require
to satisfy itself that the issuance of Shares to be purchased pursuant to the exercise of Share Options under the Plan and any subsequent resale of the Shares will be in compliance with applicable laws and regulations. In the event the Optionee
chooses to pay the purchase price by previously-owned Shares through the attestation method, the number of Shares transferred to the Optionee upon the exercise of the Share Option shall be net of the Shares attested to. 

(b) The Shares purchased upon exercise of this Share Option shall be transferred to the Optionee on the records of the Company or of the
transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the
Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder of, or to have any of the rights of a holder with respect to, any Shares subject to this Share Option unless and until
this Share Option shall have been exercised pursuant to the terms hereof, the Company or the transfer agent shall have transferred the shares to the Optionee, and the Optionee’s name shall have been entered as the shareholder of record on the
books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership rights with respect to such Shares. 

  
 2 

 (c) The minimum number of Shares with respect to which this Share Option may be exercised at any
one time shall be 100 Shares, unless the number of shares with respect to which this Share Option is being exercised is the total number of Shares subject to exercise under this Share Option at the time. 

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Share Option shall be exercisable after the Expiration Date
hereof. 
 3. Termination of Employment. If the Optionee’s employment by the Company or a Subsidiary (as defined in the Plan) is
terminated, the period within which to exercise the Shares Option may be subject to earlier termination as set forth below. 
 (a)
Termination Due to Death. If the Optionee’s employment terminates by reason of the Optionee’s death, any portion of this Share Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be
exercised by the Optionee’s legal representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date of death shall terminate
immediately and be of no further force or effect. 
 (b) Termination Due to Disability. If the Optionee’s employment terminates
by reason of the Optionee’s disability (as determined by the Administrator), any portion of this Share Option outstanding on such date, to the extent exercisable on the date of such termination of employment, may thereafter be exercised by the
Optionee for a period of 12 months from the date of disability or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date of disability shall terminate immediately and be of no further force or
effect. 
 (c) Termination for Cause. If the Optionee’s employment terminates for Cause, any portion of this Share Option
outstanding on such date shall terminate immediately and be of no further force and effect. For purposes hereof, “Cause” shall mean, unless otherwise provided in an employment agreement between the Company and the Optionee, a determination
by the Administrator that the Optionee shall be dismissed as a result of (i) any material breach by the Optionee of any agreement between the Optionee and the Company; (ii) the conviction of, indictment for or plea of nolo contendere by
the Optionee to a felony or a crime involving moral turpitude; or (iii) any material misconduct or willful and deliberate non-performance (other than by reason of disability) by the Optionee of the Optionee’s duties to the Company. 

(d) Other Termination. If the Optionee’s employment terminates for any reason other than the Optionee’s death, the
Optionee’s disability or Cause, and unless otherwise determined by the Administrator, any portion of this Share Option outstanding on such date may be exercised, to the extent exercisable on the date of termination, for a period of three months
from the date of termination or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date of termination shall terminate immediately and be of no further force or effect. 

  
 3 

 The Administrator’s determination of the reason for termination of the Optionee’s
employment shall be conclusive and binding on the Optionee and his or her representatives or legatees. 
 4. Incorporation of Plan.
Notwithstanding anything herein to the contrary, this Share Option shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms
in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein. 
 5.
Transferability. This Agreement is personal to the Optionee, is non-assignable and is not transferable in any manner, by operation of law or otherwise, other than by will or the laws of descent and distribution. This Share Option is
exercisable, during the Optionee’s lifetime, only by the Optionee, and thereafter, only by the Optionee’s legal representative or legatee. 

6. Tax Withholding. The Optionee shall, not later than the date as of which the exercise of this Share Option becomes a taxable event
for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the
authority to cause the minimum required tax withholding obligation to be satisfied, in whole or in part, by withholding from Shares to be issued to the Optionee a number of Shares with an aggregate Fair Market Value that would satisfy the minimum
withholding amount due. 
 7. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a
result of the Plan or this Agreement to continue the Optionee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Optionee at any time.

 8. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Share Option and
supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 9. Data Privacy Consent. In
order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all
personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan
and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information;
(ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the
Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable
law. 

  
 4 

 10. Notices. Notices hereunder shall be mailed or delivered to the Company at its
principal place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

			
	MIMECAST LIMITED
		
	By:	 	  

		 	Title:

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable. 
  

							
	Dated:	 	  
	 		 	  

		 		 		 	Optionee’s Signature
				
		 		 		 	Optionee’s name and address:
				
		 		 		 	  

				
		 		 		 	  

				
		 		 		 	  

  
 5 

 NON-QUALIFIED SHARE OPTION AGREEMENT 

FOR NON-EMPLOYEE DIRECTORS 

UNDER THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

									
	Name of Optionee:	 	     
	 	
				
	No. of Option Shares:	 	  
	 		 	
					
	Option Exercise Price per Share:	 	$	 	  
	 		 	
				
	Grant Date:	 	  
	 		 	
				
	Expiration Date:	 	  
	 		 	

 Pursuant to the Mimecast Limited 2015 Share Option and Incentive Plan as amended through the date hereof (the
“Plan”), Mimecast Limited (the “Company”) hereby grants to the Optionee named above, who is a member of the Board but is not an employee of the Company, an option (the “Share Option”) to purchase on or prior to the
Expiration Date specified above all or part of the number of Ordinary Shares of the Company (the “Shares”) specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth herein and in
the Plan. This Share Option is not intended to be an “incentive stock option” under Section 422 of the Internal Revenue Code of 1986, as amended. 

1. Exercisability Schedule. No portion of this Share Option may be exercised until such portion shall have become exercisable. Except
as set forth below, and subject to the discretion of the Administrator (as defined in Section 2 of the Plan) to accelerate the exercisability schedule hereunder, this Share Option shall be exercisable with respect to the following number of
Option Shares on the dates indicated so long as the Optionee remains in service as a member of the Board on such dates: 
  

					
	Incremental Number of
Option Shares Exercisable	 	 	Exercisability Date
		
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	
	 	                 (    	%) 	 	

 Once exercisable, this Share Option shall continue to be exercisable at any time or times prior
to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan. 
 2. Manner of Exercise. 

(a) The Optionee may exercise this Share Option only in the following manner: from time to time on or prior to the Expiration Date of this
Share Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be
purchased. 
 Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by
certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of Shares that have been purchased by the Optionee on the open market or that are beneficially owned by the
Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; (iii) by the Optionee delivering to the Company a properly executed exercise
notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to pay the option
purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment procedure; (iv) by
a “net exercise” arrangement pursuant to which the Company will reduce the number of Shares issuable upon exercise by the largest whole number of Shares with a Fair Market Value that does not exceed the aggregate exercise price; or
(v) a combination of (i), (ii), (iii) and (iv) above. Payment instruments will be received subject to collection. 
 The
transfer to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above,
(ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and (iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require
to satisfy itself that the issuance of Shares to be purchased pursuant to the exercise of Share Options under the Plan and any subsequent resale of the Shares will be in compliance with applicable laws and regulations. In the event the Optionee
chooses to pay the purchase price by previously-owned Shares through the attestation method, the number of Shares transferred to the Optionee upon the exercise of the Share Option shall be net of the Shares attested to. 

(b) The Shares purchased upon exercise of this Share Option shall be transferred to the Optionee on the records of the Company or of the
transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the
Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder of, or to have any of the rights of a 

  
 2 

 
holder with respect to, any Shares subject to this Share Option unless and until this Share Option shall have been exercised pursuant to the terms hereof, the Company or the transfer agent shall
have transferred the Shares to the Optionee, and the Optionee’s name shall have been entered as the shareholder of record on the books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership rights with
respect to such Shares. 
 (c) The minimum number of Shares with respect to which this Share Option may be exercised at any one time shall
be 100 Shares, unless the number of Shares with respect to which this Share Option is being exercised is the total number of Shares subject to exercise under this Share Option at the time. 

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Share Option shall be exercisable after the Expiration Date
hereof. 
 3. Termination as Director. If the Optionee ceases to be a member of the Board, the period within which to exercise the
Share Option may be subject to earlier termination as set forth below. 
 (a) Termination Due to Death. If the Optionee’s
service as a member of the Board terminates by reason of the Optionee’s death, any portion of this Share Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be exercised by the Optionee’s legal
representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date of death shall terminate immediately and be of no further force
or effect. 
 (b) Other Termination. If the Optionee ceases to be a member of the Board for any reason other than the Optionee’s
death, any portion of this Share Option outstanding on such date may be exercised, to the extent exercisable on the date the Optionee ceased to be a member of the Board, for a period of six months from the date the Optionee ceased to be a member of
the Board or until the Expiration Date, if earlier. Any portion of this Share Option that is not exercisable on the date the Optionee ceases to be a member of the Board shall terminate immediately and be of no further force or effect. 

4. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Share Option shall be subject to and governed by all
the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified
herein. 
 5. Transferability. This Agreement is personal to the Optionee, is non-assignable and is not transferable in any manner,
by operation of law or otherwise, other than by will or the laws of descent and distribution. This Share Option is exercisable, during the Optionee’s lifetime, only by the Optionee, and thereafter, only by the Optionee’s legal
representative or legatee. 
 6. No Obligation to Continue as a Director. Neither the Plan nor this Share Option confers upon the
Optionee any rights with respect to continuance as a member of the Board. 

  
 3 

 7. Integration. This Agreement constitutes the entire agreement between the parties with
respect to this Share Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 8.
Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant
Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or
desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant
Companies all Relevant Information; (ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and
(iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will
only be used in accordance with applicable law. 

  
 4 

 9. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal
place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

			
	MIMECAST LIMITED
		
	By:	 	  

		 	Title:

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable. 
  

							
	Dated:	 	  
	 		 	  

		 		 		 	Optionee’s Signature
				
		 		 		 	Optionee’s name and address:
				
		 		 		 	  

				
		 		 		 	  

				
		 		 		 	  

  
 5 

 RESTRICTED SHARE AWARD AGREEMENT 

UNDER THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

							
	Name of Grantee:	 	  
	 	
				
	No. of Shares:	 	  
	 		 	
				
	Grant Date:	 	  
	 		 	

 Pursuant to the Mimecast Limited 2015 Share Option and Incentive Plan (the “Plan”) as amended
through the date hereof, Mimecast Limited (the “Company”) hereby grants a Restricted Share Award (an “Award”) to the Grantee named above. Upon acceptance of this Award, the Grantee shall receive the number Ordinary Shares of the
Company (the “Shares”) specified above, subject to the restrictions and conditions set forth herein and in the Plan. The Company acknowledges the receipt from the Grantee of consideration with respect to the nominal value of the Shares in
the form of cash, past or future services rendered to the Company by the Grantee or such other form of consideration as is acceptable to the Administrator. 

1. Award. The Restricted Shares awarded hereunder shall be issued and held by the Company’s transfer agent in book entry form, and
the Grantee’s name shall be entered as the shareholder of record on the books of the Company. Thereupon, the Grantee shall have all the rights of a shareholder with respect to such Shares, including voting and dividend rights, subject, however,
to the restrictions and conditions specified in Paragraph 2 below. The Grantee shall (i) sign and deliver to the Company a copy of this Award Agreement and (ii) deliver to the Company a stock power endorsed in blank. 

2. Restrictions and Conditions. 

(a) Any book entries for the Restricted Shares granted herein shall bear an appropriate legend, as determined by the Administrator in its sole
discretion, to the effect that such Shares are subject to restrictions as set forth herein and in the Plan. 
 (b) Restricted Shares granted
herein may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of by the Grantee prior to vesting. 
 (c) If the
Grantee’s employment with the Company and its Subsidiaries is voluntarily or involuntarily terminated for any reason (including death) prior to vesting of the Restricted Shares granted herein, all Restricted Shares shall immediately and
automatically be forfeited and returned to the Company. 
 3. Vesting of Restricted Shares. The restrictions and conditions in
Paragraph 2 of this Agreement shall lapse on the Vesting Date or Dates specified in the following schedule so long as the Grantee remains an employee of the Company or a Subsidiary on such Dates. If a series of Vesting Dates is specified, then
the restrictions and conditions in Paragraph 2 shall lapse only with respect to the number of Restricted Shares specified as vested on such date. 

					
	Incremental Number
of Shares Vested	 	 	Vesting Date
		
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	

 Subsequent to such Vesting Date or Dates, the Shares on which all restrictions and conditions have lapsed
shall no longer be deemed Restricted Shares. The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 3. 

4. Dividends. Dividends on Restricted Shares shall be paid currently to the Grantee. 

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Award shall be subject to and governed by all the terms
and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein. 

6. Transferability. This Agreement is personal to the Grantee, is non-assignable and is not transferable in any manner, by operation of
law or otherwise, other than by will or the laws of descent and distribution. 
 7. Tax Withholding. The Grantee shall, not later
than the date as of which the receipt of this Award becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law
to be withheld on account of such taxable event. Except in the case where an election is made pursuant to Paragraph 8 below, the Company shall have the authority to cause the required minimum tax withholding obligation to be satisfied, in whole or
in part, by withholding from Shares to be issued or released by the transfer agent a number of Shares with an aggregate Fair Market Value that would satisfy the minimum withholding amount due. 

8. Election Under Section 83(b). The Grantee and the Company hereby agree that the Grantee may, within 30 days following the Grant
Date of this Award, file with the Internal Revenue Service and the Company an election under Section 83(b) of the Internal Revenue Code. In the event the Grantee makes such an election, he or she agrees to provide a copy of the election to the
Company. The Grantee acknowledges that he or she is responsible for obtaining the advice of his or her tax advisors with regard to the Section 83(b) election and that he or she is relying solely on such advisors and not on any statements or
representations of the Company or any of its agents with regard to such election. 
 9. No Obligation to Continue Employment. Neither
the Company nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Grantee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to
terminate the employment of the Grantee at any time. 

  
 2 

 10. Integration. This Agreement constitutes the entire agreement between the parties with
respect to this Award and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 11. Data
Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may
process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the
administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant
Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the
transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance
with applicable law. 

  
 3 

 12. Notices. Notices hereunder shall be mailed or delivered to the Company at its
principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

			
	MIMECAST LIMITED
		
	By:	 	  

		 	Title:

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable. 
  

							
	Dated:	 	  
	 		 	  

		 		 		 	Grantee’s Signature
				
		 		 		 	Grantee’s name and address:
				
		 		 		 	  

				
		 		 		 	  

				
		 		 		 	  

  
 4 

 RESTRICTED SHARE UNIT AWARD AGREEMENT 

FOR COMPANY EMPLOYEES 

UNDER THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

							
	Name of Grantee:	 	  
	 	
				
	No. of Restricted Share Units:	 	  
	 		 	
				
	Grant Date:	 	  
	 		 	

 Pursuant to the Mimecast Limited 2015 Share Option and Incentive Plan as amended through the date hereof (the
“Plan”), Mimecast Limited (the “Company”) hereby grants an award of the number of Restricted Share Units listed above (an “Award”) to the Grantee named above. Each Restricted Share Unit shall relate to one Ordinary
Shares of the Company (the “Shares”). 
 1. Restrictions on Transfer of Award. This Award may not be sold, transferred,
pledged, assigned or otherwise encumbered or disposed of by the Grantee, and any Shares issuable with respect to the Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of until (i) the Restricted Share
Units have vested as provided in Paragraph 2 of this Agreement and (ii) Shares have been issued to the Grantee in accordance with the terms of the Plan and this Agreement. 

2. Vesting of Restricted Share Units. The restrictions and conditions of Paragraph 1 of this Agreement shall lapse on the Vesting
Date or Dates specified in the following schedule so long as the Grantee remains an employee of the Company or a Subsidiary on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 1 shall
lapse only with respect to the number of Restricted Share Units specified as vested on such date. 
  

					
	Incremental Number of
Restricted Share Units Vested	 	 	Vesting Date
		
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	

 The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 2. 

3. Termination of Employment. If the Grantee’s employment with the Company and its Subsidiaries terminates for any reason
(including death or disability) prior to the satisfaction of the vesting conditions set forth in Paragraph 2 above, any Restricted Share Units that have not vested as of such date shall automatically and without notice terminate and be forfeited,
and neither the Grantee nor any of his or her successors, heirs, assigns, or personal representatives will thereafter have any further rights or interests in such unvested Restricted Share Units. 

 4. Issuance of Shares. As soon as practicable following each Vesting Date (but in no event
later than two and one-half months after the end of the year in which the Vesting Date occurs), the Company shall issue to the Grantee the number of Shares equal to the aggregate number of Restricted Share Units that have vested pursuant to
Paragraph 2 of this Agreement on such date and the Grantee shall thereafter have all the rights of a shareholder of the Company with respect to such Shares. 

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Agreement shall be subject to and governed by all the
terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

 6. Tax Withholding. The Grantee shall, not later than the date as of which the receipt of this Award becomes a taxable event for
Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the
authority to cause the required minimum tax withholding obligation to be satisfied, in whole or in part, by withholding from Shares to be issued to the Grantee a number of Shares with an aggregate Fair Market Value that would satisfy the withholding
amount due. 
 7. Section 409A of the Code. This Agreement shall be interpreted in such a manner that all provisions relating to
the settlement of the Award are exempt from the requirements of Section 409A of the Code as “short-term deferrals” as described in Section 409A of the Code. 

8. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this
Agreement to continue the Grantee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Grantee at any time. 

9. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Award and supersedes all prior
agreements and discussions between the parties concerning such subject matter. 
 10. Data Privacy Consent. In order to administer
the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional
data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the
“Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the
Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction
in which the Relevant 

  
 2 

 
Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law. 

11. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or
delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

			
	MIMECAST LIMITED
		
	By:	 	  

		 	Title:

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable. 
  

							
	Dated:	 	  
	 		 	  

		 		 		 	Grantee’s Signature
				
		 		 		 	Grantee’s name and address:
				
		 		 		 	  

				
		 		 		 	  

				
		 		 		 	  

  
 3 

 RESTRICTED SHARE UNIT AWARD AGREEMENT 

FOR NON-EMPLOYEE DIRECTORS 

UNDER THE MIMECAST LIMITED 

2015 SHARE OPTION AND INCENTIVE PLAN 
  

							
	Name of Grantee:	 	  
	 	
				
	No. of Restricted Share Units:	 	  
	 		 	
				
	Grant Date:	 	  
	 		 	

 Pursuant to the Mimecast Limited 2015 Share Option and Incentive Plan as amended through the date hereof (the
“Plan”), Mimecast Limited (the “Company”) hereby grants an award of the number of Restricted Share Units listed above (an “Award”) to the Grantee named above. Each Restricted Share Unit shall relate to one Ordinary
Share of the Company (the “Shares”). 
 1. Restrictions on Transfer of Award. This Award may not be sold, transferred,
pledged, assigned or otherwise encumbered or disposed of by the Grantee, and any Shares issuable with respect to the Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of until (i) the Restricted Share
Units have vested as provided in Paragraph 2 of this Agreement and (ii) Shares have been issued to the Grantee in accordance with the terms of the Plan and this Agreement. 

2. Vesting of Restricted Share Units. The restrictions and conditions of Paragraph 1 of this Agreement shall lapse on the Vesting
Date or Dates specified in the following schedule so long as the Grantee remains in service as a member of the Board on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 1 shall lapse only
with respect to the number of Restricted Share Units specified as vested on such date. 
  

					
	Incremental Number of
Restricted Share Units Vested	 	 	Vesting Date
		
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	
	 	                (    	%) 	 	

 The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 2. 

3. Termination of Service. If the Grantee’s service with the Company and its Subsidiaries terminates for any reason (including
death or disability) prior to the satisfaction of the vesting conditions set forth in Paragraph 2 above, any Restricted Share Units that have not vested as of such date shall automatically and without notice terminate and be forfeited, and neither
the Grantee nor any of his or her successors, heirs, assigns, or personal representatives will thereafter have any further rights or interests in such unvested Restricted Share Units. 

 4. Issuance of Shares. As soon as practicable following each Vesting Date (but in no event
later than two and one-half months after the end of the year in which the Vesting Date occurs), the Company shall issue to the Grantee the number of Shares equal to the aggregate number of Restricted Share Units that have vested pursuant to
Paragraph 2 of this Agreement on such date and the Grantee shall thereafter have all the rights of a shareholder of the Company with respect to such Shares. 

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Agreement shall be subject to and governed by all the
terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

 6. Section 409A of the Code. This Agreement shall be interpreted in such a manner that all provisions relating to the
settlement of the Award are exempt from the requirements of Section 409A of the Code as “short-term deferrals” as described in Section 409A of the Code. 

7. No Obligation to Continue as a Director. Neither the Plan nor this Award confers upon the Grantee any rights with respect to
continuance as a member of the Board. 
 8. Integration. This Agreement constitutes the entire agreement between the parties with
respect to this Award and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 9. Data
Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may
process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the
administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant
Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the
transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance
with applicable law. 

  
 2 

 10. Notices. Notices hereunder shall be mailed or delivered to the Company at its
principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

			
	MIMECAST LIMITED
		
	By:	 	  

		 	Title:

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable. 
  

							
	Dated:	 	  
	 		 	  

		 		 		 	Grantee’s Signature
				
		 		 		 	Grantee’s name and address:
				
		 		 		 	  

				
		 		 		 	  

				
		 		 		 	  

  
 3EX-10.10

 Exhibit 10.10 

MIMECAST LIMITED 
 2015
EMPLOYEE SHARE PURCHASE PLAN 
 The purpose of the Mimecast Limited 2015 Employee Stock Purchase Plan (“the Plan”) is to
provide eligible employees of Mimecast Limited (the “Company”) and each Designated Subsidiary (as defined in Section 11) with opportunities to purchase ordinary shares of the Company (the “Ordinary Shares”).
[                ]1 Ordinary Shares have been approved and reserved for this purpose. The Plan is intended to
constitute an “employee stock purchase plan” within the meaning of Section 423(b) of the Internal Revenue Code of 1986, as amended (the “Code”), and shall be interpreted in accordance with that intent. 

1. Administration. The Plan will be administered by the person or persons (the “Administrator”) appointed by the
Company’s Board of Directors (the “Board”) for such purpose. The Administrator has authority at any time to: (i) adopt, alter and repeal such rules, guidelines and practices for the administration of the Plan and for its own acts
and proceedings as it shall deem advisable; (ii) interpret the terms and provisions of the Plan; (iii) make all determinations it deems advisable for the administration of the Plan; (iv) decide all disputes arising in connection with
the Plan; and (v) otherwise supervise the administration of the Plan. All interpretations and decisions of the Administrator shall be binding on all persons, including the Company and the Participants. No member of the Board or individual
exercising administrative authority with respect to the Plan shall be liable for any action or determination made in good faith with respect to the Plan or any option granted hereunder. 

2. Offerings The Company may make one or more offerings to eligible employees to purchase Ordinary Shares under the Plan
(“Offerings”). Unless otherwise determined by the 
  

	1 	 A number equal to 2.0% of total shares outstanding post-IPO. 

 
Administrator, an Offering will begin on the first business day occurring on or after each January 1 and July 1 and will end on the last business day occurring on or before the
following June 30 and December 31, respectively. The Administrator may, in its discretion, designate a different period for any Offering, provided that no Offering shall exceed six months in duration or overlap any other Offering. 

3. Eligibility. All individuals classified as employees on the payroll records of the Company and each Designated Subsidiary are
eligible to participate in any one or more of the Offerings under the Plan, provided that as of the first day of the applicable Offering (the “Offering Date”) they are customarily employed by the Company or a Designated Subsidiary for more
than 20 hours a week. Notwithstanding any other provision herein, individuals who are not contemporaneously classified as employees of the Company or a Designated Subsidiary for purposes of the Company’s or applicable Designated
Subsidiary’s payroll system are not considered to be eligible employees of the Company or any Designated Subsidiary and shall not be eligible to participate in the Plan. In the event any such individuals are reclassified as employees of the
Company or a Designated Subsidiary for any purpose, including, without limitation, common law or statutory employees, by any action of any third party, including, without limitation, any government agency, or as a result of any private lawsuit,
action or administrative proceeding, such individuals shall, notwithstanding such reclassification, remain ineligible for participation. Notwithstanding the foregoing, the exclusive means for individuals who are not contemporaneously classified as
employees of the Company or a Designated Subsidiary on the Company’s or Designated Subsidiary’s payroll system to become eligible to participate in this Plan is through an amendment to this Plan, duly executed by the Company, which
specifically renders such individuals eligible to participate herein. 

  
 2 

 4. Participation. 

(a) Participants. An eligible employee who is not a Participant on any Offering Date may participate in such Offering by submitting an
enrollment form to his or her appropriate payroll location at least 15 business days before the Offering Date (or by such other deadline as shall be established by the Administrator for the Offering). 

(b) Enrollment. The enrollment form will (a) state a whole percentage to be deducted from an eligible employee’s Compensation
(as defined in Section 11) per pay period, (b) authorize the purchase of Ordinary Shares in each Offering in accordance with the terms of the Plan and (c) specify the exact name or names in which Ordinary Shares purchased for such
individual are to be issued pursuant to Section 10. An employee who does not enroll in accordance with these procedures will be deemed to have waived the right to participate. Unless a Participant files a new enrollment form or withdraws from
the Plan, such Participant’s deductions and purchases will continue at the same percentage of Compensation for future Offerings, provided he or she remains eligible. 

(c) Notwithstanding the foregoing, participation in the Plan will neither be permitted nor be denied contrary to the requirements of the Code.

 5. Employee Contributions. Each eligible employee may authorize payroll deductions at a minimum of one percent up to a
maximum of ten percent of such employee’s Compensation for each pay period. The Company will maintain book accounts showing the amount of payroll deductions made by each Participant for each Offering. No interest will accrue or be paid on
payroll deductions. 
 6. Deduction Changes. Except as may be determined by the Administrator in advance of an Offering, a
Participant may not increase or decrease his or her payroll deduction 

  
 3 

 
during any Offering, but may increase or decrease his or her payroll deduction with respect to the next Offering (subject to the limitations of Section 5) by filing a new enrollment form at
least 15 business days before the next Offering Date (or by such other deadline as shall be established by the Administrator for the Offering). The Administrator may, in advance of any Offering, establish rules permitting a Participant to increase,
decrease or terminate his or her payroll deduction during an Offering. 
 7. Withdrawal. A Participant may withdraw from
participation in the Plan by delivering a written notice of withdrawal to his or her appropriate payroll location. The Participant’s withdrawal will be effective as of the next business day. Following a Participant’s withdrawal, the
Company will promptly refund such individual’s entire account balance under the Plan to him or her (after payment for any Ordinary Shares purchased before the effective date of withdrawal). Partial withdrawals are not permitted. Such an
employee may not begin participation again during the remainder of the Offering, but may enroll in a subsequent Offering in accordance with Section 4. 

8. Grant of Options. On each Offering Date, the Company will grant to each eligible employee who is then a Participant in the Plan an
option (“Option”) to purchase on the last day of such Offering (the “Exercise Date”), at the Option Price hereinafter provided for, the lowest of (a) a number of Ordinary Shares determined by dividing such Participant’s
accumulated payroll deductions on such Exercise Date by the Option Price (as defined herein),
(b) [                ]2 shares, or (c) such other lesser maximum number of shares as shall have been
established by the Administrator in advance of the Offering; provided, however, that such Option shall be subject to the limitations set forth below. Each Participant’s Option shall be exercisable only to the extent 

 

	2 	 A number approximately equal to 0.5%-1% of the post-IPO outstanding. 

  
 4 

 
of such Participant’s accumulated payroll deductions on the Exercise Date. The purchase price for each share purchased under each Option (the “Option Price”) will be 85 percent of
the Fair Market Value of the Ordinary Shares on the Offering Date or the Exercise Date, whichever is less. 
 Notwithstanding the foregoing,
no Participant may be granted an option hereunder if such Participant, immediately after the option was granted, would be treated as owning stock possessing five percent or more of the total combined voting power or value of all classes of
stock of the Company or any Parent or Subsidiary (as defined in Section 11). For purposes of the preceding sentence, the attribution rules of Section 424(d) of the Code shall apply in determining the stock ownership of a Participant, and
all stock which the Participant has a contractual right to purchase shall be treated as stock owned by the Participant. In addition, no Participant may be granted an Option which permits his or her rights to purchase stock under the Plan, and any
other employee stock purchase plan of the Company and its Parents and Subsidiaries, to accrue at a rate which exceeds $25,000 of the fair market value of such stock (determined on the option grant date or dates) for each calendar year in which the
Option is outstanding at any time. The purpose of the limitation in the preceding sentence is to comply with Section 423(b)(8) of the Code and shall be applied taking Options into account in the order in which they were granted. 

9. Exercise of Option and Purchase of Shares. Each employee who continues to be a Participant in the Plan on the Exercise Date shall be
deemed to have exercised his or her Option on such date and shall acquire from the Company such number of whole Ordinary Shares reserved for the purpose of the Plan as his or her accumulated payroll deductions on such date will purchase at the
Option Price, subject to any other limitations contained in the Plan. Any 

  
 5 

 
amount remaining in a Participant’s account at the end of an Offering solely by reason of the inability to purchase a fractional share will be carried forward to the next Offering; any other
balance remaining in a Participant’s account at the end of an Offering will be refunded to the Participant promptly. 
 10. Issuance
of Certificates. Certificates representing Ordinary Shares purchased under the Plan may be issued only in the name of the employee, in the name of the employee and another person of legal age as joint tenants with rights of survivorship, or in
the name of a broker authorized by the employee to be his, her or their, nominee for such purpose. 
 11. Definitions. 

The term “Compensation” means the amount of base pay. 

The term “Designated Subsidiary” means any present or future Subsidiary (as defined below) that has been designated by the Board to
participate in the Plan. The Board may so designate any Subsidiary, or revoke any such designation, at any time and from time to time, either before or after the Plan is approved by the stockholders. The current list of Designated Subsidiaries is
attached hereto as Appendix A. 
 The term “Fair Market Value of the Ordinary Shares” on any given date means the fair market
value of the Ordinary Shares determined in good faith by the Administrator; provided, however, that if the Ordinary Shares are admitted to quotation on the National Association of Securities Dealers Automated Quotation System (“NASDAQ”),
NASDAQ Global Market or another national securities exchange, the determination shall be made by reference to the closing price on such date. If there is no closing price for such date, the determination shall be made by reference to the last date
preceding such date for which there is a closing price. 

  
 6 

 The term “Initial Public Offering” means the first underwritten, firm commitment public
offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, covering the offer and sale by the Company of its equity securities, or such other event as a result of or following which the Company’s
Ordinary Shares shall be publicly held. 
 The term “Parent” means a “parent corporation” with respect to the Company,
as defined in Section 424(e) of the Code. 
 The term “Participant” means an individual who is eligible as determined in
Section 3 and who has complied with the provisions of Section 4. 
 The term “Subsidiary” means a “subsidiary
corporation” with respect to the Company, as defined in Section 424(f) of the Code. 
 12. Rights on Termination of
Employment. If a Participant’s employment terminates for any reason before the Exercise Date for any Offering, no payroll deduction will be taken from any pay due and owing to the Participant and the balance in the Participant’s
account will be paid to such Participant or, in the case of such Participant’s death, to his or her designated beneficiary as if such Participant had withdrawn from the Plan under Section 7. An employee will be deemed to have terminated
employment, for this purpose, if the corporation that employs him or her, having been a Designated Subsidiary, ceases to be a Subsidiary, or if the employee is transferred to any corporation other than the Company or a Designated Subsidiary. An
employee will not be deemed to have terminated employment for this purpose if the employee is on an approved leave of absence for military service or sickness or for any other purpose approved by the Company, if the employee’s right to
reemployment is guaranteed either by a statute or by contract or under the policy pursuant to which the leave of absence was granted or if the Administrator otherwise provides in writing. 

  
 7 

 13. Special Rules. Notwithstanding anything herein to the contrary, the Administrator may
adopt special rules applicable to the employees of a particular Designated Subsidiary, whenever the Administrator determines that such rules are necessary or appropriate for the implementation of the Plan in a jurisdiction where such Designated
Subsidiary has employees; provided that such rules are consistent with the requirements of Section 423(b) of the Code. Any special rules established pursuant to this Section 13 shall, to the extent possible, result in the employees subject
to such rules having substantially the same rights as other Participants in the Plan. 
 14. Optionees Not Stockholders. Neither the
granting of an Option to a Participant nor the deductions from his or her pay shall constitute such Participant a holder of the Ordinary Shares covered by an Option under the Plan until such shares have been purchased by and issued to him or her.

 15. Rights Not Transferable. Rights under the Plan are not transferable by a Participant other than by will or the laws of descent
and distribution, and are exercisable during the Participant’s lifetime only by the Participant. 
 16. Application of Funds.
All funds received or held by the Company under the Plan may be combined with other corporate funds and may be used for any corporate purpose. 

17. Adjustment in Case of Changes Affecting Ordinary Shares. In the event of a subdivision of outstanding Ordinary Shares, the payment
of a dividend in Ordinary Shares or any other change affecting the Ordinary Shares, the number of shares approved for the Plan and the share limitation set forth in Section 8 shall be equitably or proportionately adjusted to give proper effect
to such event. 

  
 8 

 18. Amendment of the Plan. The Board may at any time and from time to time amend the Plan
in any respect, except that without the approval within 12 months of such Board action by the stockholders, no amendment shall be made increasing the number of shares approved for the Plan or making any other change that would require stockholder
approval in order for the Plan, as amended, to qualify as an “employee stock purchase plan” under Section 423(b) of the Code. 

19. Insufficient Shares. If the total number of Ordinary Shares that would otherwise be purchased on any Exercise Date plus the number
of shares purchased under previous Offerings under the Plan exceeds the maximum number of shares issuable under the Plan, the shares then available shall be apportioned among Participants in proportion to the amount of payroll deductions accumulated
on behalf of each Participant that would otherwise be used to purchase Ordinary Shares on such Exercise Date. 
 20. Termination of the
Plan. The Plan may be terminated at any time by the Board. Upon termination of the Plan, all amounts in the accounts of Participants shall be promptly refunded. 

21. Governmental Regulations. The Company’s obligation to sell and deliver Ordinary Shares under the Plan is subject to obtaining
all governmental approvals required in connection with the authorization, issuance, or sale of such stock. 
 22. Governing Law. This
Plan and all Options and actions taken thereunder shall be governed by, and construed in accordance with, the laws of the State of Delaware, applied without regard to conflict of law principles. 

  
 9 

 23. Issuance of Shares. Shares may be issued upon exercise of an Option from authorized
but unissued Ordinary Shares, from shares held in the treasury of the Company, or from any other proper source. 
 24. Tax
Withholding. Participation in the Plan is subject to any minimum required tax withholding on income of the Participant in connection with the Plan. Each Participant agrees, by entering the Plan, that the Company and its Subsidiaries shall have
the right to deduct any such taxes from any payment of any kind otherwise due to the Participant, including shares issuable under the Plan. 

25. Notification Upon Sale of Shares. Each Participant agrees, by entering the Plan, to give the Company prompt notice of any
disposition of shares purchased under the Plan where such disposition occurs within two years after the date of grant of the Option pursuant to which such shares were purchased. 

26. Effective Date and Approval of Shareholders. The Plan shall take effect on the date of the Company’s Initial Public Offering,
subject to approval by the holders of a majority of the votes cast at a meeting of stockholders at which a quorum is present or by written consent of the stockholders. 

  
 10 

 APPENDIX A 

Designated Subsidiaries 
 Mimecast
North America, Inc. 

[                          
              ]

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