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                                                                    Exhibit 10.5


THIS NOTE AND ANY SECURITIES ISSUABLE UPON THE CONVERSION OF THIS NOTE HAVE NOT
BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE
TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS THEY HAVE BEEN REGISTERED UNDER SUCH
ACT OR PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER SUCH ACT.

THE PAYMENT OF THIS NOTE AND THE RIGHTS OF THE HOLDER OF THIS NOTE ARE
SUBORDINATED TO THE PAYMENT OF SUPERIOR INDEBTEDNESS AND THE RIGHTS OF THE
HOLDERS OF SUPERIOR INDEBTEDNESS UPON THE TERMS OF SUBORDINATION SET FORTH IN
THAT CERTAIN SUBORDINATION AGREEMENT DATED DECEMBER 12, 2000 BY AMONG THE ISSUER
OF THIS NOTE AND CMGI, INC., AS AMENDED, MODIFIED AND SUPPLEMENTED FROM TIME TO
TIME.

                                    FORM OF

                                NAVISITE, INC.

                     7.5% Convertible, Subordinated Note
                             Due December 12, 2003



U.S. $30,000,000                                                          [Date]

               FOR VALUE RECEIVED, the undersigned, NaviSite, Inc., a Delaware
 corporation (the "Borrower"), hereby promises to pay to CMGI, Inc., a Delaware
 corporation (the "Lender"), the principal sum of Thirty Million Dollars
 ($30,000,000) (the "Principal Sum"), or such lesser amount as may then be
 outstanding, together with accrued but unpaid interest thereon, on December 12,
 2003 (the "Maturity Date"). Interest on the outstanding Principal Sum shall be
 at a rate of 7.5% per annum ("Interest"), calculated on the basis of a 360 day
 year consisting of twelve 30 day months and payable quarterly in arrears on
 January 31, April 30, July 31 and October 31 of each year until this Note is
 paid in full (each an "Interest Payment Date"). If all or a portion of the
 Principal Sum or Interest shall not be paid when due (whether at its stated
 maturity, by acceleration or otherwise), the Borrower hereby promises to pay,
 on demand, interest on such overdue amount from and including the due date to,
 but excluding, the date such amount is paid in full at 10.5% per annum (and
 until the date such overdue amount is paid in full, "Interest" on such overdue
 amount shall mean interest at such rate).
<PAGE>

          This Note is being delivered pursuant to that certain Note and Warrant
 Purchase Agreement, dated as of December 12, 2000, between the Borrower and the
 Lender (the "Note and Warrant Purchase Agreement"). All capitalized terms used
 but not otherwise defined herein shall have the meaning ascribed to such terms
 in the Note and Warrant Purchase Agreement.

     1.   Subordination.

     The Lender's right to payment pursuant to the terms of this Note shall be
subordinated to the extent and on the terms and conditions set forth in the
Subordination Agreement, dated as of December 12, 2000, by and among the Lender
and the Borrower (the "Subordination Agreement"), and the terms and provisions
of the Subordination Agreement are incorporated herein by reference.

     2.   Payment.

          Payment of the Principal Sum on the Maturity Date and Interest on each
Interest Payment Date shall be made by certified or bank cashier's check payable
to the Lender at the Lender's principal address set forth in Section 6 hereof
(or at such other place as the Lender hereof shall notify the Borrower in
writing) or, if the Lender so specifies, by written notice to the Borrower given
not less than two Business Days prior to the Maturity Date or the Interest
Payment Date, as the case may be, by bank wire transfer, in immediately
available funds, to the account so specified, in lawful money of the United
States of America, provided that, at the election of the Borrower, the amount of
                   -------- ----
Interest due on any Interest Payment Date may be paid in shares of common stock,
par value $0.01 per share ("Common Stock"), of the Borrower, with the number of
shares of Common Stock to be issued in payment of the Interest due on such
Interest Payment Date to equal the amount of such Interest divided by the
average of the closing prices per share of the Common Stock on the Nasdaq
National Market as reported in The Wall Street Journal on the five consecutive
                               -----------------------
trading days ending on the trading day immediately preceding such Interest
Payment Date. The Borrower may prepay this Note at any time, without premium or
penalty, in whole or in part, with accrued interest to the date of such payment
on the amount prepaid. If the Maturity Date or any Interest Payment Date occurs
on a date that is not a Business Day then the Principal Sum or Interest then due
shall be paid on the next succeeding Business Day. "Business Day" shall mean any
day other than Saturday, Sunday or any day upon which banks in the city of
Boston, Massachusetts are authorized or required to be closed.

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<PAGE>

     3.   Conversion.

          (a)  Conversion Rights.  Subject to and in accordance with the
               -----------------
provisions of this Section 3, at any time on or prior to the Maturity Date, the
Lender may elect, in its sole discretion, to effect the conversion (the
"Conversion") of all or any portion of the Principal Sum and Interest due on
this Note into Common Stock. The number of shares of Common Stock into which the
Principal Sum and accrued but unpaid Interest (or portion thereof) shall be
converted pursuant to this Section 3(a) shall be determined by dividing the
amount of Principal Sum and Interest the Lender has elected to convert by the
Conversion Price. The Conversion Price is subject to adjustment as provided in
Section 4 hereof.

          (b)  Mandatory Conversion.  Subject to the provisions of Section 3(c)
               --------------------
hereof, if there is a Mandatory Conversion Event (as defined below) at any time
on or prior to the Maturity Date, the Borrower shall have the right to require
the conversion of all, but not less than all, of the outstanding Principal Sum
and Interest into Common Stock at the Conversion Price (the "Mandatory
Conversion") in accordance with Sections 3(a) and 3(c) hereof.

          (c)  Manner of Effecting the Conversion. If the Lender elects to
               ----------------------------------
effect the Conversion pursuant to Section 3(a) hereof, the Lender shall deliver
a duly executed written notice to the Borrower of such election (the "Conversion
Notice"), and in such event the Conversion shall be deemed to have been effected
at the close of business on the date such Conversion Notice is given. If the
Borrower elects to effect the Mandatory Conversion pursuant to Section 3(b)
hereof, the Borrower shall deliver a duly executed written notice to the Lender
(the "Mandatory Conversion Notice") within ten Business Days of any period of 20
consecutive trading days during which the closing price per share of the Common
Stock as reported on the Nasdaq National Market exceeds 175% of the Conversion
Price on at least 15 trading days (a "Mandatory Conversion Event"), and in such
event the Mandatory Conversion shall be deemed to have been effected at the
close of business on the date such Mandatory Conversion Notice is given. Upon
any Conversion or Mandatory Conversion of this Note in accordance with the terms
hereof, the rights of the Lender with respect to the Principal Sum and all
Interest pursuant to this Note shall cease and the Lender shall be deemed to
have become the holder of record of the shares of Common Stock into which this
Note shall have been converted, provided that, if the Lender elects to convert
                                -------- ----
only a portion of the Principal Sum and Interest pursuant to Section 3(a)
hereof, then the Borrower will deliver a new note to the Lender, on the same
terms and conditions as this Note, with respect to the portion of the Principal
Sum and Interest that is not converted (the "New Note"). Concurrently with the
delivery of a Conversion Notice or receipt of a Mandatory Conversion Notice, as
the case may be, the Lender shall surrender this Note to the Borrower. Promptly
upon its receipt of a Conversion Notice or delivery of a Mandatory Conversion
Notice, as the

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<PAGE>

case may be, the Borrower shall (i) deliver to or upon the written order of the
Lender, a certificate or certificates for the number of shares of Common Stock
issuable upon such Conversion or Mandatory Conversion, (ii) make a cash payment
in respect of any fraction of a share as provided in Section 3(d) hereof and
(iii) if applicable, deliver a New Note as set forth in this Section 3(c).

          (d)  Fractional Shares.  No fractional shares shall be issued upon any
               -----------------
Conversion or Mandatory Conversion. Instead of any fractional share which would
otherwise be issuable upon a Conversion or Mandatory Conversion, the Borrower
shall pay a cash amount in respect of such fractional share in an amount based
upon the Conversion Price.

     4.   Antidilution Provisions.

          (a)  Reorganization, Reclassification or Recapitalization of the
               -----------------------------------------------------------
Borrower. In case of (i) a capital reorganization, reclassification or
--------
recapitalization of the Borrower's capital stock (other than in the cases
referred to in Section 4(c) hereof), (ii) the Borrower's consolidation or merger
with or into another corporation in which the Borrower is not the surviving
entity, or a merger in which the Borrower is the surviving entity but the shares
of the Borrower's capital stock outstanding immediately prior to the merger are
converted, by virtue of the merger, into other property, whether in the form of
securities, cash or otherwise, or (iii) the sale or transfer of all or
substantially all of the Borrower's assets, then, as part of such
reorganization, reclassification, recapitalization, merger, consolidation, sale
or transfer, lawful provision shall be made so that there shall thereafter be
deliverable upon the Conversion or Mandatory Conversion of the Principal Sum and
Interest or any portion thereof (in lieu of or in addition to the number of
shares of Common Stock theretofore deliverable, as appropriate) and without
payment of any additional consideration, the number of shares of stock or other
securities or property to which the holder of the number of shares of Common
Stock which would otherwise have been deliverable upon the Conversion or
Mandatory Conversion of the Principal Sum and Interest or any portion thereof at
the time of such reorganization, reclassification, recapitalization,
consolidation, merger, sale or transfer would have been entitled to receive in
such reorganization, reclassification, recapitalization, consolidation, merger,
sale or transfer. This Section 4(a) shall apply to successive reorganizations,
reclassifications, recapitalizations, consolidations, mergers, sales and
transfers and to the stock or securities of any other corporation that are at
the time receivable upon the Conversion or Mandatory Conversion of the Principal
Sum and Interest or any portion thereof. If the per share consideration payable
to the Lender for shares of Common Stock in connection with any transaction
described in this Section 4(a) is in a form other than cash or marketable
securities, then the value of such consideration shall be determined in good
faith by the Borrower's board of directors.

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<PAGE>

               (b)  Splits and Combinations.  If the Borrower at any time or
                    -----------------------
from time to time after the date of this Note subdivides any of its outstanding
shares of Common Stock into a greater number of shares, the Conversion Price in
effect immediately prior to such subdivision shall be proportionately reduced,
and, conversely, if the outstanding shares of Common Stock are combined into a
smaller number of shares, the Conversion Price in effect immediately prior to
such combination shall be proportionately increased.

               (c)  Reclassifications.  If the Borrower reclassifies or
                    -----------------
otherwise changes any of the securities into which this Note may be convertible
into the same or a different number of securities of any other class or classes,
this Note shall thereafter be convertible into such number and kind of
securities as would have been issuable as the result of such change with respect
to the securities that this Note was convertible into immediately prior to such
reclassification or other change and the Conversion Price therefor shall be
appropriately adjusted.

               (d)  Adjustment Certificates.  Upon any adjustment of the
                    -----------------------
Conversion Price or the number of shares of Common Stock issuable upon the
Conversion or Mandatory Conversion of this Note, a certificate, signed by (i)
the Borrower's President and Chief Financial Officer or (ii) any independent
firm of certified public accountants of recognized national standing the
Borrower selects at its own expense, setting forth in reasonable detail the
events requiring the adjustment and the method by which such adjustment was
calculated, shall be mailed to the Lender at the address set forth in Section 6
hereof and shall specify the adjusted Conversion Price and the number of shares
of Common Stock issuable upon the Conversion or Mandatory Conversion of the Note
after giving effect to the adjustment.

               (e)  No Impairment.  The Borrower shall not, by amendment of its
                    -------------
Certificate of Incorporation or through any reorganization, recapitalization,
transfer of assets, consolidation, merger, dissolution, issue or sale of
securities or any other voluntary action, avoid or seek to avoid the observance
or performance of any of the terms to be observed or performed hereunder by the
Borrower, but shall at all times in good faith assist in the carrying out of all
provisions of this Section 4 and in the taking of all such action as may be
necessary or appropriate in order to protect the rights of the Lender against
impairment. The Borrower shall not be deemed to have avoided or to be seeking to
avoid the observance or performance of any of the terms to be observed or
performed hereunder by issuing securities after the Closing Date for a
consideration per share less than the Conversion Price then in effect.

               (f)  Application.  Except as otherwise provided herein, all
                    -----------
sections of this Section 4 are intended to operate independently of one another.
If an event

                                       5
<PAGE>

occurs that requires the application of more than one section, all applicable
sections shall be given independent effect.

     5.   Default and Remedies.

          (a)    If any of the following events or conditions (each an "Event of
Default") shall occur and be continuing:

          (i)    the Borrower shall fail to pay the Principal Sum when and as
                 the same shall become due and payable, whether at its stated
                 maturity, by acceleration or otherwise;

          (ii)   the Borrower shall fail to pay any Interest within 30 days of
                 when and as the same shall become due and payable, whether at
                 its stated maturity, by acceleration or otherwise;

          (iii)  upon or after the occurrence of a default with respect to any
                 other outstanding indebtedness of the Borrower for borrowed
                 money the holder thereof declares all obligations with respect
                 to such indebtedness to be due and payable prior to the stated
                 maturity or regularly scheduled dates of payment with respect
                 to such indebtedness;

          (iv)   if the Stockholders' Meeting is required, the Borrower fails to
                 hold the Stockholders' Meeting in accordance with Section 5 of
                 the Note and Warrant Purchase Agreement;

          (v)    the Borrower fails to grant and deliver the Warrants in
                 accordance with the terms of the Note and Warrant Purchase
                 Agreement;

          (vi)   an involuntary proceeding shall be commenced or an involuntary
                 petition shall be filed in a court of competent jurisdiction
                 seeking (A) relief in respect of the Borrower, or of a
                 substantial part of the property or assets of the Borrower,
                 under Title 11 of the United States Code, as now constituted or
                 hereafter amended, or any successor to or replacement of such
                 statute, or any other Federal or state bankruptcy, insolvency,
                 receivership or similar law, (B) the appointment of a receiver,
                 trustee, custodian, sequestrator, conservator or similar
                 official for the Borrower or for a substantial part of the
                 properties or assets of the Borrower or (C) the winding-up,
                 liquidation or dissolution of the Borrower; and such proceeding
                 or petition

                                       6
<PAGE>

                 shall continue undismissed for 90 days or an order or decree
                 approving or ordering any of the foregoing shall be entered; or

          (vii)  the Borrower (A) voluntarily commences any proceeding or files
                 any petition seeking relief under Title 11 of the United States
                 Code, as now constituted or hereafter amended, or any successor
                 to or replacement of such statute, or any other Federal or
                 state bankruptcy, insolvency, receivership or similar law, (B)
                 consents to, or fails to contest in a timely and appropriate
                 manner, the commencement against of any proceeding or the
                 filing of any petition described in clause (v) above, (C)
                 applies for or consents to the appointment of a receiver,
                 trustee, custodian, sequestrator, conservator or similar
                 official for the Borrower or for a substantial part of the
                 properties or assets of the Borrower, (D) files an answer
                 admitting the material allegations of a petition filed against
                 it in any such proceeding, (E) makes a general assignment for
                 the benefit of creditors, (F) becomes unable, admits in writing
                 its inability or fails generally to pay its debts as they
                 become due or (G) takes any action for the purpose of effecting
                 any of the foregoing;

then, (x) in the case of an Event of Default specified in clause (a)(i), (ii),
(iii), (iv) or (v) above, the Lender may, at any time during the continuance of
such Event of Default, by written notice to the Borrower, declare the entire
outstanding Principal Sum, together with all accrued and unpaid Interest, to be
due and payable and (y) in the case of an Event of Default specified in clauses
(a)(vi) or (vii) above, the entire outstanding Principal Sum, together with all
accrued and unpaid Interest, shall automatically forthwith become due and
payable without presentment, protest or notice of any kind, all of which are
hereby expressly waived by the Borrower.

          (b)  Subject to the other terms of this Note, if an Event of Default
occurs and is continuing, the Lender may pursue any available remedy to collect
the payment of the Principal Sum or Interest or to enforce the performance of
any provision of this Note. If an Event of Default occurs and is continuing, the
Lender may proceed to protect and enforce its rights by any action at law, suit
in equity or other appropriate proceeding. In the case of a default in the
payment of the Principal Sum or Interest, the Borrower will pay to the Lender
such further amount as shall be sufficient to cover the costs and expenses of
collection, including, without limitation, reasonable attorneys' fees, expenses
and disbursements.

                                       7
<PAGE>

          (c)  The Borrower shall promptly furnish the Lender notice of any
Event of Default or event which, with notice, lapse of time or both, would
become an Event of Default under this Section 5.

     6.   Notices

          All notices, instructions and other communications given hereunder or
in connection herewith shall be in writing. Any such notice, instruction or
communication shall be sent either (i) by certified mail, return receipt
requested, postage prepaid, (ii) via a reputable nationwide overnight courier
service or (iii) by facsimile (with "answer-back" confirmation), in each case to
the address set forth below. Any such notice, instruction or communication shall
be deemed to have been delivered upon receipt of confirmation of delivery after
it is sent by certified mail, return receipt requested, postage prepaid, one
Business Day after it is sent via a reputable nationwide overnight courier
service, or upon receipt of confirmation of delivery of a facsimile.

If to the Borrower to:        NaviSite, Inc.
                              400 Minuteman Road
                              Andover, MA 01810
                              Attention: General Counsel
                              Facsimile: (978) 682-8100

With a copy to:               Hale and Dorr LLP
                              60 State Street
                              Boston, MA 02109
                              Attention: Mark G. Borden, Esq.
                              Facsimile: (617) 526-5000

If to the Lender to:          CMGI, Inc.
                              100 Brickstone Square
                              Andover, MA 01810
                              Attention: William Williams, II, Esq.
                              Facsimile: (978) 684-3601

With a copy to:               Skadden, Arps, Slate Meagher & Flom LLP
                              One Beacon Street
                              Boston, MA 02108
                              Attention: David T. Brewster, Esq.
                              Facsimile: (617) 573-4822

                                       8
<PAGE>

Either party may give any notice, instruction or communication in connection
with this Note using any other means (including personal delivery or ordinary
mail), but no such notice, instruction or communication shall be deemed to have
been delivered unless and until it is received by the party to whom it was sent.
Either party may change the address to which notices, instructions or
communications are to be delivered by giving the other party to this Note notice
thereof in the manner set forth in this Section 6.

     7.   Miscellaneous.

          This Note shall be construed and enforced in accordance with the laws
of the Commonwealth of Massachusetts, without regard to its conflicts of laws
rules. The Borrower waives presentment, demand, notice, protest and all other
demands and notices in connection with the delivery, acceptance, performance,
default and enforcement of this Note. The Borrower hereby irrevocably and
unconditionally submits, for itself and its property, to the non-exclusive
jurisdiction of the courts of the Commonwealth of Massachusetts and of the
United States District Court for the District of Massachusetts, and any
appellate court of such courts, in any action or proceeding arising out of or
relating to this Note, or for recognition or enforcement of any judgment, and
the Borrower hereby irrevocably and unconditionally agrees that all claims in
respect of any such action or proceeding may be heard and determined in such
Massachusetts court (or, to the extent permitted by law, in such federal court).
The Borrower agrees that a final, unappealable judgment in any such action or
proceeding shall be conclusive and may be enforced in other jurisdictions by
suit on the judgment or in any other manner provided by law. Nothing in this
Note shall affect any right that the Lender may otherwise have to bring any
action or proceeding relating to this Note against the Borrower or its
properties in the courts of any jurisdiction.

THE LENDER AND THE BORROWER AGREE THAT NEITHER OF THEM NOR ANY ASSIGNEE OR
SUCCESSOR SHALL (A) SEEK A JURY TRIAL IN ANY LAWSUIT, PROCEEDING, COUNTERCLAIM
OR ANY OTHER ACTION BASED UPON, OR ARISING OUT OF, THIS NOTE, ANY RELATED
INSTRUMENTS, ANY COLLATERAL OR THE DEALINGS OR THE RELATIONSHIP BETWEEN OR AMONG
ANY OF THEM, OR (B) SEEK TO CONSOLIDATE ANY SUCH ACTION WITH ANY OTHER ACTION IN
WHICH A JURY TRIAL CANNOT BE OR HAS NOT BEEN WAIVED. THE PROVISIONS OF THIS
PARAGRAPH HAVE BEEN FULLY DISCUSSED BY THE LENDER AND THE BORROWER, AND THESE
PROVISIONS SHALL BE SUBJECT TO NO EXCEPTIONS. NEITHER THE LENDER NOR THE
BORROWER HAS AGREED WITH OR REPRESENTED TO THE OTHER THAT

                                       9
<PAGE>

THE PROVISIONS OF THIS PARAGRAPH WILL NOT BE FULLY ENFORCED IN ALL INSTANCES.

               If any provision of this Note shall be held invalid or
unenforceable by any court of competent jurisdiction, that holding shall not
invalidate or render unenforceable any other provision hereof.

               This Note and all rights hereunder are freely transferable by the
holder hereof, subject to compliance with applicable state and federal
securities laws.

               This Note may not be changed, amended or modified except by
agreement in writing signed by the Borrower and the Lender.




           [The remainder of this page is intentionally left blank.]

                                       10
<PAGE>

               IN WITNESS WHEREOF, the Borrower has caused this Note to be
signed on its behalf, in its corporate name, by its duly authorized officer as
an instrument under seal, as of the day and year first above written.

                                         NAVISITE, INC.




                                         By ____________________________________
                                          Name:
                                          Title:

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