<PAGE>

                                                                   EXHIBIT 10.12
                                                                   -------------

                                NAVISITE, INC.

                           INVESTOR RIGHTS AGREEMENT

     This Agreement dated as of __________, 1999 is entered into by and among
NaviSite, Inc., a Delaware corporation (the "Company"), and CMGI, Inc., a
Delaware corporation (the "Investor").

                                   Recitals
                                   --------

     WHEREAS, the Company desires to undertake an initial public offering of its
Common Stock; and

     WHEREAS, in order to induce the Investor to approve such offering, the
Company has agreed to provide for certain arrangements with respect to (i) the
registration of shares of capital stock of the Company under the Securities Act
of 1933, as amended, and (ii) the Investor's right of first refusal with respect
to certain issuances of securities of the Company;

     NOW, THEREFORE, in consideration of the mutual promises and covenants
contained in this Agreement, the parties hereto agree as follows:


     I. - Certain Definitions.
          -------------------

     As used in this Agreement, the following terms shall have the following
respective meanings:

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

     "Common Stock" means the common stock, $.01 par value 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
issued under such Act, as they each may, from time to time, be in effect.
<PAGE>

     "Initiating Holders" means the Stockholders initiating a request for
      ------------------
registration pursuant to Section 2.1(a) or 2.1(b), as the case may be.

     "Initial Public Offering" means the initial underwritten public offering of
      -----------------------
shares of Common Stock pursuant to an effective Registration Statement.

     "Other Holders" shall have the meaning set forth in Section 2.2(b).
      -------------

     "Permitted Transferee" shall have the meaning set forth in Section 3.3.
      --------------------

     "Prospectus" means the prospectus included in any Registration Statement,
      ----------
as amended or supplemented by an amendment or prospectus supplement, including
post-effective amendments, and all material incorporated by reference or deemed
to be incorporated by reference in such Prospectus.

     "Registration Statement" means a registration statement filed by the
      ----------------------
Company with the Commission for a public offering and sale of securities of the
Company (other than a registration statement on Form S-8 or Form S-4, or their
successors, or any other form for a similar limited purpose, or any registration
statement covering only securities proposed to be issued in exchange for
securities or assets of another corporation).

     "Registration Expenses" means the expenses described in Section 2.4.
      ---------------------

     "Registrable Shares" means (a) the shares of Common Stock held by the
      ------------------
Investor upon the closing of the Initial Public Offering and (b) any other
shares of Common Stock issued in respect of such shares (because of stock
splits, stock dividends, reclassifications, recapitalizations or similar
events); provided, however, that shares of Common Stock which are Registrable
         --------  -------
Shares shall cease to be Registrable Shares upon (i) any sale pursuant to a
Registration Statement or Rule 144 under the Securities Act or (ii) any sale in
any manner to a person or entity which, by virtue of Section 3.4 of this
Agreement, is not entitled to the rights provided by this Agreement.

     "Securities Act" means the Securities Act of 1933, as amended, or any
      --------------
successor federal statute, and the rules and regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

                                       2
<PAGE>

     "Selling Stockholder" means any Stockholder owning Registrable Shares
      -------------------
included in a Registration Statement.

     "Stockholders" means the Investor and any persons or entities to whom the
      ------------
rights granted under this Agreement are transferred by the Investor, its
successors or assigns, pursuant to Section 3.4 hereof.

     II. - Registration Rights
           -------------------

               2.1  Required Registrations.
                    ----------------------

                    (a)  At any time following 180 days after the closing of the
Initial Public Offering, a Stockholder or Stockholders may request, in writing,
that the Company effect the registration on Form S-1 or Form S-2 (or any
successor form) of Registrable Shares owned by such Stockholder or Stockholders
having an aggregate value of at least $10,000,000 (based on the then current
public market price).

                    (b)  At any time after the Company becomes eligible to file
a Registration Statement on Form S-3 (or any successor form relating to
secondary offerings), a Stockholder or Stockholders may request, in writing,
that the Company effect the registration on Form S-3 (or such successor form),
of Registrable Shares having an aggregate value of at least $2,500,000 (based on
the then current public market price).

                    (c)  Upon receipt of any request for registration pursuant
to this Section 2.1, the Company shall promptly give written notice of such
proposed registration to all other Stockholders. Such Stockholders shall have
the right, by giving written notice to the Company within 15 days after the
Company provides its notice, to elect to have included in such registration such
of their Registrable Shares as such Stockholders may request in such notice of
election, subject in the case of an underwritten offering to the approval of the
managing underwriter as provided in Section 2.1(d) below. Thereupon, the Company
shall, as expeditiously as possible, use its best efforts to effect the
registration on an appropriate registration form of all Registrable Shares which
the Company has been requested to so register (provided, however, that in the
case of a registration requested under Section 2.1(b), the Company will only be
obligated to effect such registration on Form S-3 (or any successor form)).

                                       3
<PAGE>

                    (d)  If the Initiating Holders intend to distribute the
Registrable Shares covered by their request by means of an underwriting, they
shall so advise the Company as a part of their request made pursuant to Section
2.1(a) or (b), as the case may be, and the Company shall include such
information in its written notice referred to in Section 2.1(c). The right of
any other Stockholder to include its Registrable Shares in such registration
pursuant to Section 2.1(a) or (b), as the case may be, shall be conditioned upon
such other Stockholder's participation in such underwriting on the terms set
forth herein. If the managing underwriter determines that the marketing factors
require a limitation of the number of shares to be underwritten, the number of
Registrable Shares to be included in a Registration Statement filed pursuant to
this Section 2.1 shall be reduced pro rata among the requesting Stockholders
based on the quotient of (1) the total Registrable Shares to be included in the
Registration Statement, divided by (2) the total number of Registrable Shares
that requested registration.

                    (e)  The Initiating Holders shall have the right to select
the managing underwriter(s) for any underwritten offering requested pursuant to
Section 2.1(a) or (b), subject to the approval of the Company, which approval
will not be unreasonably withheld.

                    (f)  The Company shall not be required to effect more than
two registrations pursuant to Section 2.1(a) or more than five registrations
pursuant to Section 2.1(b). In addition, the Company shall not be required to
effect any registration within 90 days after the effective date of any other
Registration Statement of the Company relating to an underwritten offering. For
purposes of this Section 2.1(f), a Registration Statement shall not be counted
until such time as such Registration Statement has been declared effective by
the Commission, unless the Initiating Holders withdraw their request for such
registration (other than as a result of information concerning the business or
financial condition of the Company which is made known to the Stockholders after
the date on which such registration was requested) and elect not to pay the
Registration Expenses therefor pursuant to Section 2.4.

                    (g)  If at the time of any request to register Registrable
Shares by Initiating Holders pursuant to this Section 2.1, the Company is
engaged or has plans to engage in a registered public offering or is engaged in
any other activity which, in the good faith determination of the Company's Board
of Directors, would be adversely affected by the requested registration or
financial statements required for the requested registration are not then
available, then the Company may at its option direct that such request be
delayed for a period not in excess of 90 days from the date

                                       4
<PAGE>

of such request, such right to delay a request to be exercised by the Company
not more than once in any 12-month period.

          2.2  Incidental Registration.
               -----------------------

               (a)  Whenever the Company proposes to file a Registration
Statement (other than a Registration Statement filed pursuant to Section 2.1) at
any time and from time to time, it will, prior to such filing, give written
notice to all Stockholders of its intention to do so; provided, that no such
notice need be given if no Registrable Shares are to be included therein as a
result of a determination of the managing underwriter pursuant to Section
2.2(b). Upon the written request of a Stockholder or Stockholders given within
20 days after the Company provides such notice (which request shall state the
intended method of disposition of such Registrable Shares), the Company shall
use its best efforts to cause all Registrable Shares which the Company has been
requested by such Stockholder or Stockholders to register to be registered under
the Securities Act to the extent necessary to permit their sale or other
disposition in accordance with the intended methods of distribution specified in
the request of such Stockholder or Stockholders; provided that the Company shall
have the right to postpone or withdraw any registration effected pursuant to
this Section 2.2 without obligation to any Stockholder.

               (b)  If the registration for which the Company gives notice
pursuant to Section 2.2(a) involves an underwriting, the Company shall so advise
the Stockholders as a part of the written notice given pursuant to Section
2.2(a). In such event, the right of any Stockholder to include its Registrable
Shares in such registration pursuant to Section 2.2 shall be conditioned upon
such Stockholder's participation in such underwriting on the terms set forth
herein. All Stockholders proposing to distribute their securities through such
underwriting shall enter into an underwriting agreement in customary form with
the underwriter or underwriters selected for the underwriting by the Company.
Notwithstanding any other provision of this Section 2.2, if the managing
underwriter determines that the inclusion of all shares requested to be
registered would adversely affect the offering, the Company may limit the number
of Registrable Shares to be included in the registration and underwriting. The
Company shall so advise all holders of Registrable Shares requesting
registration, and the number of shares that are entitled to be included in the
registration and underwriting shall be allocated in the following manner. The
securities of the Company held by holders other than Stockholders and other
stockholders entitled to include shares therein ("Other Holders") shall be
excluded from such registration and underwriting to the extent deemed advisable
by the managing underwriter, and, if a further limita-

                                       5
<PAGE>

tion on the number of shares is required, the number of shares that may be
included in such registration and underwriting shall be allocated among all
Stockholders and Other Holders requesting registration in proportion, as nearly
as practicable, to the respective number of shares of Common Stock which they
held at the time the Company gives the notice specified in Section 2.2(a). If
any Stockholder or Other Holder would thus be entitled to include more
securities than such holder requested to be registered, the excess shall be
allocated among other requesting Stockholders and Other Holders pro rata in the
manner described in the preceding sentence. If any holder of Registrable Shares
or any Other Holder disapproves of the terms of any such underwriting, such
person may elect to withdraw therefrom by written notice to the Company, and any
Registrable Shares or other securities excluded or withdrawn from such
underwriting shall be withdrawn from such registration.

                    (c)  Notwithstanding the foregoing, the Company shall not be
required, pursuant to this Section 2.2, to include any Registrable Shares in a
Registration Statement if such Registrable Shares can then be sold pursuant to
Rule 144(k) under the Securities Act and represent less than 1% of the then
outstanding shares of Common Stock.

          2.3       Registration Procedures.
                    -----------------------

                    (a)  If and whenever the Company is required by the
provisions of this Agreement to use its best efforts to effect the registration
of any Registrable Shares under the Securities Act, the Company shall:

                              (i)  file with the Commission a Registration
     Statement with respect to such Registrable Shares and use its best efforts
     to cause that Registration Statement to become effective as soon as
     possible;

                              (ii) as expeditiously as possible, prepare and
     file with the Commission any amendments and supplements to the
     Registration Statement and the prospectus included in the Registration
     Statement as may be necessary to comply with the provisions of the
     Securities Act (including the anti-fraud provisions thereof) and to keep
     the Registration Statement effective for 12 months from the effective date
     or such lesser period until all such Registrable Shares are sold;

                                       6
<PAGE>

                              (iii) as expeditiously as possible, furnish to
     each Selling Stockholder such reasonable numbers of copies of the
     Prospectus, including any preliminary Prospectus, in conformity with the
     requirements of the Securities Act, and such other documents as such
     Selling Stockholder may reasonably request in order to facilitate the
     public sale or other disposition of the Registrable Shares owned by such
     Selling Stockholder;

                              (iv)  as expeditiously as possible, use its best
     efforts to register or qualify the Registrable Shares covered by the
     Registration Statement under the securities or Blue Sky laws of such states
     as the Selling Stockholders shall reasonably request and do any and all
     other acts and things that may be necessary or desirable to enable the
     Selling Stockholders to consummate the public sale or other disposition in
     such states of the Registrable Shares owned by the Selling Stockholder;
     provided, however, that the Company shall not be required in connection
     --------  -------
     with this paragraph (iv) to qualify as a foreign corporation or execute a
     general consent to service of process in any jurisdiction;

                              (v)   as expeditiously as possible, cause all such
     Registrable Shares to be listed on each securities ex change or automated
     quotation system on which similar securities issued by the Company are then
     listed; and

                              (vi)  promptly make available for inspection by
     the Selling Stockholders, any managing underwriter participating in any
     disposition pursuant to such Registration Statement and any attorney or
     accountant or other agent retained by any such underwriter or selected by
     the Selling Stockholders, all financial and other records, pertinent
     corporate documents and properties of the Company and cause the Company's
     officers, directors, employees and independent accountants to supply all
     information reasonably requested by any such seller, underwriter,
     attorney, accountant or agent in connection with such Registration
     Statement.

                    (b)  If the Company has delivered a Prospectus to the
Selling Stockholders, and after having done so, the Prospectus is amended to
comply with the requirements of the Securities Act, the Company shall promptly
notify the

                                       7
<PAGE>

Selling Stockholders and, if requested, the Selling Stockholders shall
immediately cease making offers of Registrable Shares and return all
Prospectuses to the Company. The Company shall promptly provide the Selling
Stockholders with revised Prospectuses, and following receipt of the revised
Prospectuses, the Selling Stock holders shall be free to resume making offers of
the Registrable Shares.

               (c)  In the event that, in the judgment of the Company, it is
advisable to suspend use of a Prospectus included in a Registration Statement
due to pending material developments or other events that have not yet been
publicly disclosed and as to which the Company believes public disclosure would
be detrimental to the Company, the Company shall notify all Selling
Stockholders to such effect, and upon receipt of such notice, each such Selling
Stockholder shall immediately discontinue any sales of Registrable Shares
pursuant to such Registration Statement until such Selling Stockholder has
received copies of a supplemented or amended Prospectus or until such Selling
Stockholder is advised in writing by the Company that the then current
Prospectus may be used and has received copies of any additional or
supplemental filings that are incorporated or deemed incorporated by reference
in such Prospectus. Notwithstanding anything to the contrary herein, the Company
shall not exercise its rights under this Section 2.3(c) to suspend sales of
Registrable Shares for a period in excess of 90 days in any 365-day period.

          2.4  Allocation of Expenses.  The Company will pay all Registration
               ----------------------
Expenses for all registrations under this Agreement; provided, however, that if
                                                     --------  -------
a registration under Section 2.1 is withdrawn at the request of the Initiating
Holders (other than as a result of information concerning the business or
financial condition of the Company which is made known to the Stockholders after
the date on which such registration was requested) and if the Initiating Holders
elect not to have such registration counted as a registration requested under
Section 2.1, the requesting Stockholders shall pay the Registration Expenses of
such registration pro rata in accordance with the number of their Registrable
Shares included in such registration. For purposes of this Section, the term
"Registration Expenses" shall mean all expenses incurred by the Company in
complying with this Agreement, including, without limitation, all registration
and filing fees, exchange listing fees, printing expenses, fees and expenses of
counsel for the Company and the fees and expenses of one counsel selected by the
Selling Stockholders to represent the Selling Stockhold  ers, state Blue Sky
fees and expenses and the expense of any special audits incident to or required
by any such registration, but excluding underwriting discounts, selling
commissions and the fees and expenses of Selling Stockholders' own counsel
(other than the counsel selected to represent all Selling Stockholders).

                                       8
<PAGE>

          2.5  Indemnification and Contribution.
               --------------------------------

               (a)  In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, the Company will
indemnify and hold harmless the seller of such Registrable Shares, each
underwriter of such Registrable Shares and each other person, if any, who
controls such seller or underwriter within the meaning of the Securities Act or
the Exchange Act against any losses, claims, damages or liabilities, joint or
several, to which such seller, under writer or controlling person may become
subject under the Securities Act, the Exchange Act, state securities or Blue Sky
laws or otherwise, insofar as such losses, claims, damages or liabilities (or
actions in respect thereof) (i) arise out of or are based upon any untrue
statement or alleged untrue statement of any material fact contained in any
Registration Statement under which such Registrable Shares were registered under
the Securities Act, any preliminary prospectus or final prospectus contained in
the Registration Statement or any amendment or supplement to such Registration
Statement or (ii) arise out of or are based upon the omission or alleged
omission to state a material fact required to be stated therein or necessary to
make the statements therein not misleading; and the Company will reimburse such
seller, underwriter and controlling person for any legal or any other expenses
reasonably incurred by such seller, underwriter or controlling person in
connection with investigating or defending any such loss, claim, damage,
liability or action; provided, however, that the Company will not be liable in
                     --------  -------
any such case to the extent that any such loss, claim, damage or liability
arises out of or is based upon any untrue statement or omission made in such
Registration Statement, preliminary prospectus or prospectus, or any such
amendment or supplement, in reliance upon and in conformity with information
furnished to the Company, in writing, by or on behalf of such seller,
underwriter or controlling person specifically for use in the preparation
thereof.

               (b)  In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, each seller of
Registrable Shares, severally and not jointly, will indemnify and hold harmless
the Company, each of its directors and officers and each underwriter (if any)
and each person, if any, who controls the Company or any such underwriter within
the meaning of the Securities Act or the Exchange Act, against any losses,
claims, damages or liabilities, joint or several, to which the Company, such
directors and officers, underwriter or controlling person may become subject
under the Securities Act, Exchange Act, state securities or Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) (i) arise out of or are based upon any untrue

                                       9
<PAGE>

statement or alleged untrue statement of a material fact contained in any
Registration Statement under which such Registrable Shares were registered under
the Securities Act, any preliminary prospectus or final prospectus contained in
the Registration Statement or any amendment or supplement to the Registration
Statement or (ii) arise out of or are based upon any omission or alleged
omission to state a material fact required to be stated therein or necessary to
make the statements therein not misleading, if the statement or omission was
made in reliance upon and in conformity with information relating to such seller
furnished in writing to the Company by or on behalf of such seller specifically
for use in connection with the preparation of such Registration Statement,
prospectus, amendment or supplement; provided, however, that the obligations of
                                     --------  -------
a Stockholder hereunder shall be limited to an amount equal to the net proceeds
to such Stockholder of Registrable Shares sold in connection with such
registration.

               (c)  Each party entitled to indemnification under this Section
2.5 (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 and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; provided, that counsel for the Indemnifying
                                --------
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not be unreasonably
withheld); and, provided, further, that the failure of any Indemnified Party to
                --------  -------
give notice as provided herein shall not relieve the Indemnifying Party of its
obligations under this Section 2.5 except to the extent that the Indemnifying
Party is adversely affected by such failure. The Indemnified Party may
participate in such defense at such Indemnified Party's expense; provided,
                                                                 --------
however, that the Indemnifying Party shall pay such expense if representation
-------
of such Indemnified Party by the counsel retained by the Indemnifying Party
would be inappropriate due to actual or potential differing interests between
the Indemnified Party and any other party represented by such counsel in such
proceeding; provided further that in no event shall the Indemnifying Party be
            -------- -------
required to pay the expenses of more than one law firm per jurisdiction as
counsel for the Indemnified Party.  The Indemnifying Party also shall be
responsible for the expenses of such defense if the Indemnifying Party does not
elect to assume such defense.  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
of such claim or litigation, and no Indemnified Party shall consent to entry of
any

                                       10
<PAGE>

judgment or settle such claim or litigation without the prior written consent of
the Indemnifying Party, which consent shall not be unreasonably withheld.

               (d)  In order to provide for just and equitable contribution in
circumstances in which the indemnification provided for in this Section 2.5 is
due in accordance with its terms but for any reason is held to be unavailable to
an Indemnified Party in respect to any losses, claims, damages and liabilities
referred to herein, then the Indemnifying Party shall, in lieu of indemnifying
such Indemnified Party, contribute to the amount paid or payable by such
Indemnified Party as a result of such losses, claims, damages or liabilities to
which such party may be subject in such proportion as is appropriate to reflect
the relative fault of the Company on the one hand and the Stockholders on the
other in connection with the statements or omissions which resulted in such
losses, claims, damages or liabilities, as well as any other relevant equitable
considerations. The relative fault of the Company and the Stockholders shall
be determined by reference to, among other things, whether the untrue or alleged
untrue statement of material fact related to information supplied by the Company
or the Stockholders and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission.
The Company and the Stockholders agree that it would not be just and equitable
if contribution pursuant to this Section 2.5 were determined by pro rata
allocation or by any other method of allocation which does not take account of
the equitable considerations referred to above. Notwithstanding the provisions
of this Section 2.5(d), (a) in no case shall any one Stockholder be liable or
responsible for any amount in excess of the net proceeds received by such
Stockholder from the offering of Registrable Shares and (b) the Company shall be
liable and responsible for any amount in excess of such proceeds; provided,
                                                                  --------
however, that no person guilty of fraudulent misrepresentation (within the
-------
meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from any person who was not guilty of such fraudulent
misrepresentation. Any party entitled to contribution will, promptly after
receipt of notice of commencement of any action, suit or proceeding against such
party in respect of which a claim for contribution may be made against another
party or parties under this Section 2.5(d), notify such party or parties from
whom contribution may be sought, but the omission so to notify such party or
parties from whom contribution may be sought shall not relieve such party from
any other obligation it may have thereunder or otherwise under this Section
2.5(d). No party shall be liable for contribution with respect to any action,
suit, proceeding or claim settled without its prior written consent, which
consent shall not be unreasonably withheld.

                                       11
<PAGE>

          2.6  Other Matters with Respect to Underwritten Offerings.  In the
               ----------------------------------------------------
event that Registrable Shares are sold pursuant to a Registration Statement in
an underwritten offering pursuant to Section 2.1, the Company agrees to enter
into an underwriting agreement containing customary representations and
warranties with respect to the business and operations of the Company and
customary covenants and agreements to be performed by the Company, including
without limitation customary provisions with respect to indemnification by the
Company of the underwriters of such offering.

          2.7  Information by Holder.  Each holder of Registrable Shares
               ---------------------
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 required in connection
with any registration, qualification or compliance referred to in this
Agreement.


     III. -  Right Of First Refusal
             ----------------------

               3.1  Rights of Investor
                    ------------------

                    (a)  Until the first date on which the Investor or any
Permitted Transferee (as defined below) owns less than a majority, by voting
power, of the outstanding shares of capital stock of the Company (assuming the
exercise and conversion of all outstanding options, warrants and convertible
securities), the Company shall not issue or sell (i) any shares of its Common
Stock, (ii) any other voting equity securities of the Company, including,
without limitation, shares of preferred stock, (iii) any option, warrant or
other right to subscribe for, purchase or otherwise acquire any voting equity
securities of the Company or (iv) any debt securities convertible into voting
capital stock of the Company (collectively, the "Offered Securities"), unless in
each such case the Company shall have first complied with this Section 3.1. The
Company shall deliver to the Investor a written notice of any proposed or
intended issuance or sale of Offered Securities (the "Offer"), which Offer shall
(A) identify and describe the Offered Securities, (B) describe the price and
other terms upon which they are to be issued or sold, and the number or amount
of the Offered Securities to be issued or sold, (C) identify the persons or
entities (if known) to which or with which the Offered Securities are to be
offered, issued or sold and (D) offer to issue and sell to the Investor a number
of the Offered Securities (the "Available Amount") such that, after the issuance
and sale of all of the Offered Securities, including the purchase of the
Available Amount by the Investor, the

                                       12
<PAGE>

Investor would own at least a majority, by voting power, of the outstanding
capital stock of the Company (assuming the exercise and conversion of all
outstanding options, warrants and convertible securities). The Company shall not
be required to offer any Offered Securities to the Investor hereunder if, after
the issuance and sale thereof, the Investor (or the Permitted Transferee) would
continue to own at least a majority, by voting power, of the outstanding capital
stock of the Company (assuming the exercise and conversion of all outstanding
options, warrants and convertible securities).

               (b)  To accept an Offer, in whole or in part, the Investor must
deliver a written notice to the Company within 20 days after its receipt of the
Offer, setting forth the portion of the Available Amount that the Investor
elects to purchase (the "Notice of Acceptance").

               (c)  The Company shall have 180 days from the expiration of the
period set forth in Section 3.1(b) above to issue or sell all or any part of
such Offered Securities as to which a Notice of Acceptance has not been given by
the Investor, upon terms and conditions which are not more favorable, in the
aggregate, to the acquiring person or persons or less favorable to the Company
than those set forth in the Offer. If the consideration to be received by the
Company from the sale of Offered Securities consists of anything other than
cash, the Board of Directors of the Company shall in good faith determine the
cash equivalent of such non-cash consideration and the Investor may pay an
equivalent portion of its purchase price for the elected portion of the
Available Amount in cash.

               (d)  The purchase by the Investor of any Offered Securities is
subject in all cases to the preparation, execution and delivery by the Company
and the Investor of a purchase agreement relating to such Offered Securities
reasonably satisfactory in form and substance to the Investor.

               (e)  The rights of the Investor under this Section 3.1 shall not
apply to the grant of options to officers, directors, consultants and employees
of the Company or any subsidiary pursuant to any plan, agreement or arrangement
approved by a vote of not less than a majority of the members of the Board of
Directors of the Company, provided, however, that if the exercise of any such
                          --------
options results in the reduction of the Investor's, or Permitted Transferee's,
ownership to less than a majority, by voting power, of the outstanding capital
stock of the Company, the Company shall so notify the Investor (or Permitted
Transferee), and the Investor or Permitted Transferee shall have the right,
within 30 days after such notice, to pur-

                                       13
<PAGE>

chase from the Company, at a price equal to the then Fair Market Value (as
defined below) thereof, such number of shares of Common Stock as would increase
its ownership to a majority, by voting power, of the outstanding capital stock
of the Company. "Fair Market Value" shall mean the average closing price of the
Common Stock on the Nasdaq National Market (or other principal securities
exchange or other interdealer quotation system on which the Common Stock is
traded or quoted), during the 10-day period ending on the day prior to the date
of purchase.

          3.2  Termination.  This Article III shall terminate upon the earlier
               -----------
of (i) the sale of all or substantially all of the assets or business of the
Company, by merger, sale of assets or otherwise, and (ii) the first date on
which the Investor (or Permitted Transferee) owns less than a majority, by
voting power, of the outstanding capital stock of the Company for 30 consecutive
days.

          3.3  Permitted Transferee.  For purposes hereof, a "Permitted
               --------------------
Transferee" shall mean any person or entity that acquires directly from the
Investor shares of Common Stock representing at least a majority of the
outstanding shares of Common Stock of the Company and to which the Investor
assigns, in writing, its rights under Section 3.1.  Upon such assignment, the
Permitted Transferee shall be considered the "Investor" for purposes of Section
3.1.

          3.4  Transfers of Rights.  The rights and obligations of the Investor
               -------------------
under Section 2 may be assigned by Investor to any person or entity that
acquires shares of Common Stock having an aggregate value of at least $2,500,000
(as adjusted in stock splits and similar events) from the Investor.  The rights
and obligations of the Investor under Section 3.1 may be assigned only to a
Permitted Transferee, and upon such assignment, the rights and obligations of
the Investor under Section 3.1 shall terminate. In the event of any such
assignment, the assignee must provide written notice of such assignment to the
Company and agree in writing to be bound by the applicable provisions of this
Agreement.

    IV. - General.
          -------

          4.1  Severability.  The invalidity or unenforceability of any
               ------------
provision of this Agreement shall not affect the validity or enforceability of
any other provision of this Agreement.

          4.2  Specific Performance.  In addition to any and all other remedies
               --------------------
that may be available at law in the event of any breach of this Agreement, each

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<PAGE>

Investor shall be entitled to specific performance of the agreements and
obligations of the Company hereunder and to such other injunctive or other
equitable relief as may be granted by a court of competent jurisdiction.

          4.3  Governing Law.  This Agreement shall be governed by and construed
               -------------
in accordance with the internal laws of the Commonwealth of Massachusetts
(without reference to the conflicts of law provisions thereof).

          4.4  Notices.  All notices, requests, consents and other
               -------
communications under this Agreement shall be in writing and shall be deemed
delivered (i) two business days after being sent by registered or certified
mail, return receipt requested, postage prepaid, or (ii) one business day after
being sent via a reputable nationwide overnight courier service guaranteeing
next business day delivery, in each case to the intended recipient as set forth
below:

     If to the Company, at NaviSite, Inc., 100 Brickstone Square, Andover,
Massachusetts 01810, Attention:  President, or at such other address or
addresses as may have been furnished in writing by the Company to the Investor;
or

     If to the Investor, at CMGI, Inc., 100 Brickstone Square, Andover,
Massachusetts 01810, or at such other address or addresses as may have been
furnished to the Company in writing by such Investor.

     Any party may give any notice, request, consent or other communication
under this Agreement using any other means (including, without limitation,
personal delivery, messenger service, telecopy, first class mail or electronic
mail), but no such notice, request, consent or other communication shall be
deemed to have been duly given unless and until it is actually received by the
party for whom it is intended. Any party may change the address to which
notices, requests, consents or other communications hereunder are to be
delivered by giving the other parties notice in the manner set forth in this
Section.

          4.5  Complete Agreement.  This Agreement constitutes the entire
               ------------------
agreement and understanding of the parties hereto with respect to the subject
matter hereof and supersedes all prior agreements and understandings relating to
such subject matter.

          4.6  Amendments and Waivers.  Any term of this Agreement may be
               ----------------------
amended or terminated and the observance of any term of this Agreement may be

                                       15
<PAGE>

waived (either generally or in a particular instance and either retroactively or
prospectively) with the written consent of the Company and the Investor.

          4.7  Pronouns.  Whenever the context may require, any pronouns used in
               --------
this Agreement shall include the corresponding masculine, feminine or neuter
forms, and the singular form of nouns and pronouns shall include the plural, and
vice versa.

          4.8  Counterparts; Facsimile Signatures.  This Agreement may be
               ----------------------------------
executed in two counterparts, each of which shall be deemed to be an original,
and both of which together shall constitute one and the same document. This
Agreement may be executed by facsimile signatures.

          4.9  Section Headings.  The section headings are for the convenience
               ----------------
of the parties and in no way alter, modify, amend, limit or restrict the
contractual obligations of the parties.

          4.1  Effective Date.  This Agreement shall become effective upon the
               --------------
closing of the Company's initial public offering of Common Stock pursuant to an
effective registration statement and shall terminate if such offering does not
close prior to March 31, 2000.

     Executed as of the date first written above.

                              NAVISITE, INC.


                              By:__________________________
                                 Name:
                                 Title:

                              CMGI, INC.


                              By:__________________________
                                 Name:
                                 Title:

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