<PAGE>
                                                                     Exhibit 4.2

                                                                  EXECUTION COPY
                                                                  --------------

                         REGISTRATION RIGHTS AGREEMENT

     AGREEMENT, made as of the 30th day of March, 2001, by and among Sybari
Software, Inc., a New York* corporation (the "Company"), those persons set forth
on Schedule 1 as Investors (each an "Investor" and collectively the
"Investors"), and those persons whose names appear on the signature page hereof
and who are designated as shareholders other than the Investors (the
"Non-Investor Shareholders" and, together with the Investors, the
"Shareholders").

     WHEREAS, the Investors are acquiring an aggregate of 1,000,000 shares of
Series A Redeemable Preferred Stock, par value $.01 per share, of the Company
(the "Series A Preferred Stock") and 50 shares of Series B Convertible
Redeemable Preferred Stock, par value $.01 per share, of the Company (the
"Series B Preferred Stock"), pursuant to the terms of Securities Purchase and
Redemption Agreement dated as of the date hereof among the Company, the
Investors and the Non-Investor Shareholders (the "Purchase Agreement"); and

     WHEREAS, it is a condition to the obligations of the Investors under the
Purchase Agreement that this Agreement be executed by the parties hereto in
order to provide the Investors with certain registration rights with respect to
the shares Series B Preferred Stock being purchased by the Investors under the
Purchase Agreement, and the parties are willing to execute this Agreement and
to be bound by the provisions hereof.

     NOW, THEREFORE, in consideration of the premises and mutual covenants
contained herein, the parties hereto agree as follows:

     1.   Certain Definitions.  As used in this Agreement, the following terms
shall have the following respective meanings:

     "Act" means the Securities Act of 1933, as amended, or any successor
federal statute, and the rules and regulations of the Commission thereunder,
all as the same shall be in effect at the time.

     "Commission" means the Securities and Exchange Commission, or any other
Federal agency at the time administering the Act.

     "Common Stock" means the Common Stock, par value $.01 per share of the
Company.

     "Exchange Act" means the Securities Exchange Act of 1934, as amended, or
any successor federal statute, and the rules and regulations of the Commission
thereunder, all as the same shall be in effect at the time.

     "Holder" means the person who is then the record owner of Registrable
Securities which have not been sold to the public.


     * In April 2004, this agreement was amended such that all references to the
terms "Company," "Common Stock," "Series A Preferred Stock," "Series B
Preferred Stock," "Registrable Securities" and similar terms relating to equity
securities of the Company shall be deemed to be, as of the effective date of
the Company's reincorporation into Delaware, references to Sybari Software,
Inc., a Delaware corporation, and its respective equity securities.
<PAGE>
     "Registrable Securities" means (i) all shares of Common Stock now owned or
hereafter acquired by any Investor, (ii) all shares of Common Stock issued or
issuable upon conversion of the Series B Preferred Stock, (iii) all shares of
Common Stock now owned or hereafter acquired by the Non-Investor Shareholders,
and (iv) any Common Stock issued in respect of the shares described in clauses
(i), (ii) or (iii) upon any stock split, stock dividend, recapitalization or
other similar event.

     The term "register" means to register under the Act and applicable state
securities laws for the purpose of effecting a public sale of securities.

     "Registration Expenses" means all expenses incurred by the Company in
compliance with Sections 2, 3 or 5 hereof, including, without limitation, all
registration and filing fees, printing expenses, transfer taxes, fees and
disbursements of counsel for the Company, blue-sky fees and expenses, fees or
transfer agents and registrars, reasonable fees and disbursements of one
counsel for all the selling Holders, and the expense of any special audits
incident to or required by any such registration.

     "Selling Expenses" means all underwriting discounts and selling
commissions applicable to the sale of Registrable Securities.

     2.   Requested Registrations
          (a)  If at any time after the earlier of (i) six (6) months after the
date of the initial public offering by the Company of its Common Stock or (ii)
September 30, 2002, the Company shall receive from one or more Investors a
written request that the Company effect the registration of Registrable
Securities the Company will:

               (i)  promptly give written notice of the proposed registration to
          all other Holders; and

               (ii) as soon as practicable, use all commercially reasonable
          efforts to effect such registration as may be so requested and as
          would permit or facilitate the sale and distribution of such portion
          of such Registrable Securities as are specified in such request,
          together with such portion of the Registrable Securities of any Holder
          or Holders joining in such request as are specified in a written
          request given within twenty (20) days after receipt of such written
          notice from the Company. If the underwriter managing the offering
          advises the Holders who have requested inclusion of their Registrable
          Securities in such registration that marketing considerations require
          a limitation on the number of shares offered, such limitation or
          cut-back shall be imposed as follows: (i) shares of the Non-Investor
          Shareholders who requested inclusion of Registrable Securities in such
          registration pursuant to Section 3 hereof shall be excluded, pro rata
          on the basis of the shares requested to be included by each until such
          time as the Investors have received aggregate proceeds from prior
          sales of their Registrable Securities and any sales proposed hereunder
          equal to $30,000,000; and (ii) shares of all Holders who requested
          inclusion of Registrable Securities in such registration shall be

                                      -2-
<PAGE>
excluded, pro rata on the basis of the shares requested to be included by each.
The Company shall not be obligated to effect, or take action to effect, any such
registration pursuant to this Section 2(a):

     (A) If the Board of Directors of the Company determines in good faith,
after consultation with and acting upon the advice of outside counsel, which
advice and dependence thereon shall be recorded in the minutes of the Board, and
the Chief Executive Officer execute an officer's certificate to such effect,
that (I) it is in possession of material, non-public information concerning an
acquisition, merger, recapitalization, consolidation, reorganization, or other
material transaction by or of the Company or concerning pending or threatened
litigation and (II) disclosure of such information would jeopardize any such
transaction or litigation and would be seriously detrimental to the Company
provided, however, that no single black-out period will be longer than ninety
(90) calendar days; provided, further, however, that no black-out period may be
imposed by the Company during the first thirty (30) calendar days after the
effectiveness of the registration statement filed pursuant to this Section 2,
and, provided, further, that the Company shall only declare one black-out period
in any twelve (12) consecutive month period. The period of effectiveness of any
registration statement in effect at the time of a black-out period and the
termination period under shall be extended for a period equal to the black-out
period;

     (B) If the Company has effected a registration less than 180 days prior to
the effective date of the registration to be effected pursuant to this Section
2(a) or if the Company has commenced preparation of a registration statement and
has notified the Holders in writing that it intends to file such registration
statement within thirty (30) days of such notification; provided that, in the
event the Company fails to file such registration statement within such thirty
(30) day period or such shorter period as may be specified in such notice, the
Company shall be required to effect the registration requested by the Holders as
soon as is practicable thereafter, but in no extent less that thirty (30) days
thereafter, provided, further, that the Company may not fail to file a
registration statement pursuant to this Subsection (B) for a period of more than
180 days in any consecutive twelve (12) month period;

     (C) In any particular jurisdiction in which the Company would be required
to execute a general consent to service of process in effecting such
registration, qualification or compliance, unless the Company is already subject
to service in such jurisdiction and except as may be required by the Securities
Act or applicable rules or regulations thereunder;

     (D) After the Company has effected two (2) such registrations on behalf of
the Investors (an "Investor Registration") pursuant to this Section 2(a) and,
such registrations have been declared or ordered effective and the sales of such
Registrable Securities shall have closed and the Investors shall have sold all

                                      -3-
<PAGE>
          of the Registrable Securities included by them in such registration,
          provided, that any registration proceeding commenced pursuant to this
          Section 2(a) that is subsequently, withdrawn at the request of a
          majority of the Investors shall count towards the Investor
          Registrations; or

               (E) If the Registrable Securities requested by one or more
          Holders to be registered pursuant to such request have an anticipated
          aggregate public offering price (before any underwriting discounts and
          commissions) of less than $5,000,000.

          (b) The underwriter of any underwriting requested under this Section 2
shall be selected the Company, which underwriter must be reasonably acceptable
to Holders holding a majority of the Registrable Securities to be included
therein.

     3. "Piggy Back" Registrations.

          (a) If the Company shall determine to register any of its securities,
either for its own account or the account of a security holder or holders
exercising their registration rights (subject to the provisions of Section 2),
other than a registration relating solely to employee benefit plans or a
registration on any registration form which does not permit secondary sales or
does not include substantially the same information as would be required to be
included in a registration statement covering the sale of Registrable Securities
or pursuant to Form S-4, the Company will:

               (i) Promptly give to each Holder of Registrable Securities
          written notice thereof (which shall include the number of shares the
          Company or other security holder proposes to register and, if known,
          the name of the proposed underwriter); and

               (ii) Use its best efforts to include in such registration all the
          Registrable Securities specified in a written request or requests,
          made by any Holder within twenty (20) days after the date of delivery
          of the written notice from the Company described in clause (i) above.
          If the underwriter advises the Company that marketing considerations
          require a limitation on the number of shares offered pursuant to any
          registration statement and the registration was for the Company's
          account, then the Company may offer all of the securities it proposes
          to register for its own account and such limitation on any remaining
          securities that may, in the opinion of the underwriter, be sold will
          be imposed as follows: (i) first shares of the Non-Investor
          Shareholders who requested inclusion of Registrable Securities in such
          registration pursuant to Section 4 hereof shall be excluded until such
          time as the Investors shall have received aggregate proceeds from
          prior sales of their Registrable Securities and any sales pursuant to
          Section 2(a) equal to $30,000,000, pro rata on the basis of the shares
          requested to be included by each; and (ii) next shares of the
          Investors who requested inclusion of Registrable Securities in such
          registration shall be excluded, pro rata on the basis of the shares
          requested to be included by each; provided, however, that in the event
          such

                                      -4-
<PAGE>
          underwriter reasonably advises the Holders who have requested
          inclusion of their Registrable Securities in such registration that
          marketing considerations require a limitation on the number of shares
          offered by specific Holders, such limitation shall be imposed in
          accordance with the underwriter's advice. If the registration is for
          the account of another security holder under Section 2, then the
          cutback shall be in accordance with the provisions of Section 2.

          (b)  The Company shall select the underwriter for an offering made
pursuant to this Section 3; provided that such underwriter must be reasonably
acceptable to the Holders of a majority of the Registrable Securities being
registered in such offering.

     4.   Expenses of Registration.  All Registration Expenses incurred in
connection with any registration, qualification or compliance pursuant to
Section 2, 3, or 5 shall be paid by the Company. All Selling Expenses incurred
in connection with any such registration, qualification or compliance shall be
borne by holders of the securities registered, pro rata on the basis of the
number of their shares so registered.

     5.   Registration on Form S-3. The Company shall use its best efforts to
qualify for registration on Form S-3 or any comparable or successor form; and
to that end the Company shall register (whether or not required by law to do
so) the Common Stock under the Exchange Act in accordance with the provisions
of the Exchange Act following the effective date of the first registration of
any securities of the Company on Form S-1 or any comparable or successor form.
After the Company has qualified for the use of Form S-3, in addition to the
rights contained in the foregoing provisions of this Agreement, the Investors
shall each have unlimited rights to request registrations on Form S-3 (such
requests shall be in writing and shall state the number of shares of
Registrable Securities to be disposed of and the intended methods of
disposition of such shares by such Holder or Holders).

     6.   Registration Procedures.  In the case of each registration effected
by the Company pursuant to this Agreement, the Company will keep each Holder of
Registrable Securities included in such registration advised in writing as to
the initiation of each registration and as to the completion thereof. At its
sole expense, the Company will do the following for the benefit of such Holders:

          (a)  Keep such registration effective for a period of 120 days or
until the Holder or Holders have completed the distribution described in the
registration statement relating thereto, whichever first occurs, and amend or
supplement such registration statement and the prospectus contained therein
from time to time to the extent necessary to comply with the Act and applicable
state securities laws provided, however, that (A) such 120 day period shall be
extended for a period of time equal to the period during which the Holders
refrain from selling any securities included in such registration in accordance
with provisions in Section 2(a) hereof; and (B) in the case of any registration
of Registrable Securities on Form S-3 which are intended to be offered on a
continuous or delayed basis, such 120 day period shall be extended until all
such Registrable Securities are sold, provided that Rule 415 promulgated by the
Commission pursuant to the Act, or any successor rule under the Act, permits an
offering on a continuous or


                                      -5-
<PAGE>
delayed basis, and provided further that applicable rules under the Act
governing the obligation to file a post-effective amendment permit, in lieu of
filing a post-effective amendment which (x) includes any prospectus required by
Section 10(a) of the Act or (y) reflects facts or events representing a material
or fundamental change in the information set forth in the registration
statement, the incorporation by reference of information required to be included
in (x) and (y) above to be contained in periodic reports filed pursuant to
Section 12 or 15(d) of the Exchange Act in the registration statement;

      (b)   Use its best efforts to register or qualify the Registrable
Securities covered by such registration under the applicable securities or "blue
sky" laws of such jurisdictions as the selling shareholders may reasonably
request; provided, that the Company shall not be obligated to qualify to do
business in any jurisdiction where it is not then so qualified or otherwise
required to be so qualified or to take any action which would subject it to the
service of process in suits other than those arising out of such registration;

      (c)   Furnish such number of prospectuses and other documents incident
thereto as a Holder from time to time may reasonably request;

      (d)   In connection with any underwritten offering pursuant to a
registration statement filed pursuant to Section 2 hereof, the Company will
enter into any underwriting agreement reasonably necessary to effect the offer
and sale of Common Stock, provided such underwriting agreement contains
customary underwriting provisions and is entered into by the Holder and provided
further that, if the underwriter so requests, the underwriting agreement will
contain customary contribution provisions on the part of the Company;

      (e)   To the extent then permitted under applicable professional
guidelines and standards, use its best efforts to obtain a comfort letter from
the Company's independent public accountants in customary form and covering such
matters of the type customarily covered by comfort letters and an opinion from
the Company's counsel in customary form and covering such matters of the type
customarily covered in a public issuance of securities, in each case addressed
to the Holders, and provide copies thereof to the Holders; and

      (f)   Permit the counsel to the selling Holders whose expenses are being
paid pursuant to Section 4 hereof to inspect and copy such corporate documents
as it may reasonably request.

   7. Indemnification.

      (a)   The Company will, and hereby does, indemnify each Holder, each of
its officers, directors and partners, and each person controlling such Holder
within the meaning of the Act, with respect to which registration, qualification
or compliance as been effected pursuant to this Agreement, and each underwriter,
if any, and each person who controls such underwriter within the meaning of the
Act, against all claims, losses, damages and liabilities (or actions in respect
thereof) arising out of or based on any untrue statement (or alleged untrue
statement) of a material fact contained in any prospectus, offering circular or
other document (including any related registration statement, notification or
the like) incident to any such


                                      -6-
<PAGE>
registration, qualification or compliance, or based on any omission (or alleged
omission) to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, or any violation by the
Company of the Act or the Exchange Act or securities act of any state or any
rule or regulation thereunder applicable to the Company and relating to action
or inaction required of the Company in connection with any such registration,
qualification or compliance, and will reimburse each such Holder, each of its
officers, directors and partners, and each person controlling such Holder, each
such underwriter and each person who controls any such underwriter, for any
legal and any other expenses reasonably incurred in connection with
investigating and defending any such claim, loss, damage, liability or action,
whether or not resulting in any liability, provided that the Company will not be
liable in any such case to the extent that any such claim, loss, damage,
liability or expense arises out of or is based on any untrue statement (or
alleged untrue statement) or omission (or alleged omission) based upon written
information furnished to the Company by such Holder or underwriter and stated to
be specifically for use therein.

          (b)  Each Holder will, if Registrable Securities held by him, her or
it are included in the securities as to which such registration, qualification
or compliance is being effected, indemnify the Company, each of its directors
and officers and each underwriter, if any, of the Company's securities covered
by such a registration statement, each person who controls the Company or such
underwriter within the meaning of the Act and the rules and regulations
thereunder, each other such Holder and each of their officers, directors and
partners, and each person controlling such Holder, against all claims, losses,
damages and liabilities (or actions in respect thereof) arising out of or based
on any untrue statement (or alleged untrue statement) of a material fact
contained in any such registration statement, prospectus, offering circular or
other document, or any omission (or alleged omission) to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, and will reimburse the Company, each person controlling
the Company, each underwriter and each person who controls any such underwriter,
each Holder and each person controlling such Holder, and their respective
directors, officers, partners, persons, underwriters and control persons for any
legal or any other expenses reasonably incurred in connection with investigating
or defending any such claim, loss, damage, liability or action, whether or not
resulting in liability, in each case to the extent, but only to the extent, that
such untrue statement (or alleged untrue statement) or omission (or alleged
omission) is made in such registration statement, prospectus, offering circular
or other document in reliance upon and in conformity with written information
furnished to the Company by such Holder and stated to be specifically for use
therein; provided, however, that the obligations of each Holder hereunder shall
be limited to an amount equal to the net proceeds received by such Holder upon
sale of his, her or its securities.

          (c)  Each party entitled to indemnification under this Section 7 (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, but the
failure of any Indemnified Party to give such notice shall not relieve the
Indemnifying Party of its obligations under this Section 7 (except and to the
extent the Indemnifying Party has been prejudiced as a consequence thereof). The
Indemnifying Party will be entitled to participate in, and to the extent that it
may elect by written




                                      -7-
<PAGE>
notice delivered to the Indemnified Party promptly after receiving the aforesaid
notice from such Indemnified Party, at its expense to assume, the defense of any
such claim or any litigation resulting therefrom, with counsel reasonably
satisfactory to such Indemnified Party, provided that the Indemnified Party may
participate in such defense at its expense, notwithstanding the assumption of
such defense by the Indemnifying Party, and provided, further, that if the
defendants in any such action shall include both the Indemnified Party and the
Indemnifying Party and the Indemnified Party shall have reasonably concluded
that there may be legal defenses available to it and/or other Indemnified
Parties which are different from or additional to those available to the
Indemnifying Party, the Indemnified Party or Parties shall have the right to
select separate counsel to assert such legal defenses and to otherwise
participate in the defense of such action on behalf of such Indemnified Party or
Parties and the fees and expenses of such counsel shall be paid by the
Indemnifying Party. No Indemnifying Party, in the defense of any such claim or
litigation, shall, except with the consent of each Indemnified Party, consent to
entry of any judgment or enter into any settlement which does not include as an
unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party of a release from all liability in respect to such claim or
litigation. Each Indemnified Party shall (i) furnish such information regarding
itself or the claim in question as an Indemnifying Party may reasonably request
in writing and as shall be reasonably required in connection with defense of
such claim and litigation resulting therefrom and (ii) shall reasonably assist
the Indemnifying Party in any such defense, provided that the Indemnified Party
shall not be required to expend its funds in connection with such assistance.

          (d)  No Holder shall be required to participate in a registration
pursuant to which it would be required to execute an underwriting agreement in
connection with a registration effected under Section 2 or 3 which imposes
indemnification or contribution obligations on such Holder more onerous than
those imposed hereunder; provided, however, that the Company shall not be deemed
to breach the provisions of Section 2 or 3 if a Holder is not permitted to
participate in a registration on account of his, her or its refusal to execute
an underwriting agreement on the basis of this subsection (d).

     8.   Lock-up Agreement. If requested by the Underwriter in any registered
public offering by the Company, the Shareholders agree not to sell or otherwise
transfer any Registration Securities for such period of time after the date of
such offering as may be requested by the underwriter, but in no event to exceed
180 days from the close of the initial registered public offering and ninety
(90) days from the close of any subsequent registered public offering, provided
that all executive officers, directors and two percent (2%) shareholders of the
Company enter into similar agreements, and each Shareholder is released from
such lock up agreement on a pro rata basis with any other Shareholder, officer,
director or two percent (2%) shareholder released from its lock up agreement.

     9.   Information by Holder. Each Holder of Registrable Securities included
in any registration shall furnish to the Company such information regarding
such Holder and the distribution proposed by such Holder as the Company may
reasonably request in writing and as shall be reasonably required in connection
with any registration, qualification or compliance referred to in this
Agreement or otherwise required by applicable state or federal securities laws.

                                      -8-
<PAGE>
     10.  Limitations on Registration Rights. From and after the date of this
Agreement, the Company shall not, without the prior written consent of the
Investors, enter into any agreement with any holder or prospective holder of
any securities of the Company which would give any such holder or prospective
holder (a) the right to require the Company, upon any registration of any of
its securities, to include, among the securities which the Company is then
registering, securities owned by such holder, unless under the terms of such
agreement, such holder or prospective holder may include such securities in any
such registration only to the extent that the inclusion of its securities will
not limit the number of Registrable Securities sought to be included by the
Holders of Registrable Securities or reduce the offering price thereof; or (b)
the right to require the Company to initiate any registration of any securities
of the Company.

     11.  Exception to Registration. The Company shall not be required to effect
a registration under this Agreement if such Holders may sell without
registration under the Act all Registrable Securities for which they requested
registration under the provisions of the Act and in the manner and in the
quantity in which the Registrable Securities were proposed to be sold; provided
that this Section 11 shall not apply to sales made under Rule 144(k) or any
successor rule promulgated by the Commission until after the effective date of
the Company's initial registration of shares under the Act. Notwithstanding the
foregoing, in no event shall the provisions of this Section 11 be construed to
preclude a Holder of Registrable Securities form exercising rights under
Section 3 for a period of three years after the effective date of the Company's
initial registration of shares under the Act.

     12.  Rule 144 Reporting. With a view to making available the benefits of
certain rules and regulations of the Commission which may permit the sale of
restricted securities (as that term is used in Rule 144 under the Act) to the
public without registration, the Company agrees to:

          (a)  make and keep public information available as those terms are
understood and defined in Rule 144 under the Act, at all times from and after
ninety (90) days following the effective date of the first registration under
the Act filed by the Company for an offering of its securities to the general
public;

          (b)  use its best efforts to file with the Commission in a timely
manner all reports and other documents required of the Company under the Act and
the Exchange Act at any time after it has become subject to such reporting
requirements; and

          (c)  as long as an Investor owns any restricted securities, furnish to
the Investor forthwith upon request a written statement by the Company as to
its compliance with the reporting requirements of Rule 144 (at any time from
and after ninety days following the effective date of the first registration
statement filed by the Company for an offering of its securities to the general
public), and of the Act   and Exchange Act (at any time after it has became
subject to such reporting requirements), a copy for the most recent annual or
quarterly report of the Company, and such other reports and documents so filed
by the Company as an



                                      -9-
<PAGE>
Investor may reasonably request in availing itself of any rule or regulation of
the Commission allowing an Investor to sell any such securities without
registration.

          13.  Listing Application. If shares of any class of stock of the
Company shall be listed on a national securities exchange, the Company shall,
at its expense, include in its listing application all of the shares of the
listed class then owned by any Investor and any Non-Investor Shareholder.

          14.  Damages. The Company recognizes and agrees that the Holder of
Registrable Securities shall not have an adequate remedy if the Company fails
to comply with the provisions of this Agreement, and that damages will not be
readily ascertainable, and the Company expressly agrees that in the event of
such failure any Holder of Registrable Securities shall be entitled to seek
specific performance of the Company's obligations hereunder and that the
Company will not oppose an application seeking such specific performance.

          15.  Miscellaneous.

               (a)  All covenants and agreements contained in this Agreement by
or on behalf of any of the parties hereto shall bind and inure to the benefit
of the respective successors and assigns of the parties hereto (including
without limitation transferees of any Registrable Securities), whether so
expressed or not.

               (b)  All notices, requests, consents and other communications
hereunder shall be in writing and shall be (i) mailed by certified or registered
mail, return receipt requested, postage prepaid (ii) sent by hand delivery,
(iii) sent by facsimile, or (iv) sent by overnight courier addressed as follows:

               If to the Company, any Non-Investor Shareholder or any Investor,
          at the address of such party set forth on Schedule I hereto or the
          most recent address as is shown on the stock records of the Company;
          and

               If to any subsequent Holder of Registrable Securities, to it as
          such address as may have been furnished to the Company in writing by
          such Holder; or, in any case, at such other address or addresses as
          shall have been furnished in writing to the Company (in the case of a
          Holder of Registrable Securities) or to the Holders of Registrable
          Securities (in the case of the Company) in accordance with the
          provisions of this paragraph.

               (c)  This Agreement shall be governed by and construed in
accordance with the laws of The Commonwealth of Massachusetts.

               (d)  This Agreement may not be amended or modified, and no
provision hereof may be waived, without the written consent of the Company, the
Investors holding at least fifty-one percent (51%) of the outstanding
Registrable Securities held by the Investors and the Non-Investor Shareholders
holding at least fifty-one percent (51%) of the outstanding Registrable
Securities held by the Non-Investor Shareholders.


                                      -10-
<PAGE>
               (e)  This Agreement may be executed in two (2) or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

               (f)  If any provision of this Agreement shall be held to be
illegal, invalid or unenforceable, such illegality, invalidity or
unenforceability shall attach only to such provision and shall not in any manner
affect or render illegal, invalid or unenforceable any other provision of this
Agreement, and this Agreement shall be carried out as if any such illegal,
invalid or unenforceable provision were not contained herein.

                                   **********

                                       11
<PAGE>
                             SYBARI SOFTWARE, INC.

                         REGISTRATION RIGHTS AGREEMENT

                           COUNTERPART SIGNATURE PAGE

     IN WITNESS WHEREOF, this Agreement has been executed as an instrument
under SEAL as of the date and year first above written.



                                        COMPANY:

                                        SYBARI SOFTWARE, INC.

                                        By: /s/ Robert G. Wallace
                                            -------------------------
                                            Name:  Robert G. Wallace
                                            Title: President


                                        INVESTORS:

                                        Summit Ventures V, L.P.

                                        By: Summit Partners V, L.P.
                                            Its General Partner

                                            By: Summit Partners, LLC
                                                Its General Partner

                                            By: /s/ Tom Roberts
                                               ----------------------
                                               Member


                                        Summit V Companion Fund, L.P.


                                       By: Summit Partners V, L.P.
                                           Its General Partner

                                           By: Summit Partners, LLC
                                               Its General Partner


                                           By: /s/ Tom Roberts
                                               -----------------------
                                               Member


                                      S-1
<PAGE>
                    Summit V Advisors Fund, L.P.

                    By: Summit Partners, LLC
                        Its General Partner

                        By: /s/ Tom Roberts
                            -------------------------
                            Member

                    Summit V Advisors Fund (QP), L.P.

                    By: Summit Partners, LLC
                        Its General Partner

                        By: /s/ Tom Roberts
                            -------------------------
                            Member

                    Summit Subordinated Debt Fund II, L.P.

                    By: Summit Partners SD II, LLC
                        Its General Partner

                        By: /s/ Tom Roberts
                            -------------------------
                            Member

                    Summit Investors III, L.P.

                    By: /s/ Tom Roberts
                        -------------------------
                        General Partner

                                      S-2



<PAGE>
                             SYBARI SOFTWARE, INC.

                         REGISTRATION RIGHTS AGREEMENT

                           Counterpart Signature Page

     IN WITNESS WHEREOF, this Agreement has been executed as an instrument
under SEAL as of the date and year first above written.

                                                  NON-INVESTOR SHAREHOLDERS:



                                                  /s/ Robert G. Wallace
                                                  --------------------------
                                                  Robert G. Wallace


                                                  /s/ Tobias Berman
                                                  --------------------------
                                                  Tobias Berman


                                                  /s/ Gregory A. Tetrault
                                                  --------------------------
                                                  Gregory A. Tetrault


                                                  /s/ Patrick A. FitzMaurice
                                                  --------------------------
                                                  Patrick A. FitzMaurice


                                                  /s/ Kenneth Toole
                                                  --------------------------
                                                  Kenneth Toole


                                                  /s/ Cheryl M. Levi
                                                  --------------------------
                                                  Cheryl M. Levi


                                                  /s/ Alexander S. Berman
                                                  --------------------------
                                                  Alexander S. Berman


                                                  /s/ Ari D. Berman
                                                  --------------------------
                                                  Ari D. Berman


                                                  /s/ Thomas Buoniello
                                                  --------------------------
                                                  Thomas Buoniello


                                                  /s/ Rocco Donnino
                                                  --------------------------
                                                  Rocco Donnino


                                      S-3










<PAGE>
                                   SCHEDULE 1
                                   ----------

COMPANY
-------

Sybari Software, Inc.
353 Larkfield Road
East Northport, NY 11731
Attn: President
Facsimile: (631) 630-8551

NON-INVESTOR SHAREHOLDERS
-------------------------

Robert G. Wallace
216 Asharoken Ave.
Asharoken, New York 11768

Tobias Berman
68-10 Dartmouth Street
Forest Hills, New York 11375

Gregory A. Tetrault
24 Stone Drive
Northport, New York 11768

Patrick A. FitzMaurice
26 Oak Street
Northport, New York 11768

Kenneth Toole
1468 Paulson Street
Wantaugh, New York 11793

Cheryl M. Levi
3555 Oxford Avenue
Riverdale, New York 10403

<PAGE>



Alexander S. Berman
14 Pinchas Rozen
Raanana 43211

Ari D. Berman
357 Central Park West
New York, New York 10024

Thomas Buoniello
16 Durham Place
Lake Grove, New York 11753

Rocco Donnino
32 Logan Hill Road
Northport, New York 11768


INVESTORS
---------

Summit Ventures V, L.P.
c/o Summit Partners
600 Atlantic Avenue, Suite 2800
Boston, Massachusetts 02210-2227
Attention: Thomas Roberts

Summit V Companion Fund, L.P.
c/o Summit Partners
600 Atlantic Avenue, Suite 2800
Boston, Massachusetts 02210-2227
Attention: Thomas Roberts

Summit V Advisors Fund, L.P.
c/o Summit Partners
600 Atlantic Avenue, Suite 2800
Boston, Massachusetts 02210-2227
Attention: Thomas Roberts
<PAGE>
Summit V Advisors Fund (QP), L.P.
c/o Summit Partners
600 Atlantic Avenue, Suite 2800
Boston, Massachusetts 02210-2227
Attention: Thomas Roberts

Summit Subordinated Debt Fund II, L.P.
c/o Summit Partners
600 Atlantic Avenue, Suite 2800
Boston, Massachusetts 02210-2227
Attention: Thomas Roberts

Summit Investors III, L.P.
c/o Summit Partners
600 Atlantic Avenue, Suite 2800
Boston, Massachusetts 02210-2227
Attention: Thomas Roberts