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                                                                   EXHIBIT 10.20

                             AMENDMENT #5 TO LEASE
                             ---------------------

1.  Parties.
    -------

    This Amendment, dated as of December 18,  2000, is between Andover Mills
Realty Limited Partnership ("Landlord") and CMGI, Inc. ("Tenant").

2.  Recitals.
    --------

    2.1  Landlord and Tenant have entered into Lease, dated as of April 12,
1999, for space in Brickstone Square in Andover, Massachusetts (as now or
hereafter amended, the "Lease").  Unless otherwise defined, terms used in this
Amendment have the same meanings as those used in the Lease.

    2.2  Tenant no longer wishes to lease the following portions of the
Premises in Building 200 (collectively, the "Terminated Space"), totaling 92,700
s.f. of agreed rentable area: Offer Space #1 (2/nd/ Floor, 29,916 s.f.); Fifth
Expansion Space #1 (3/rd/ Floor, 14,198 s.f.); Fifth Expansion Space #2 (3/rd/
Floor, 15,695 s.f.); and the Temporary Space (5/th/ Floor, 32,891 s.f.).
Accordingly, Landlord and Tenant have agreed that Tenant will assign and
transfer its interest in the Terminated Space to Landlord and that the Lease
will then terminate with respect to the Terminated Space only.  In order to
accomplish this and other matters, for good and valuable consideration, the
receipt and sufficiency of which is acknowledged, the parties agree and the
Lease is amended as follows as of the date hereof, notwithstanding anything to
the contrary:

3.  Amendments.
    ----------

    3.1  As of the date hereof, Tenant assigns, conveys and transfers to
Landlord all of Tenant's right, title and interest in and to the Terminated
Space, and: (a) the Lease will terminate and expire as to the Terminated Space
only and Tenant and its Affiliates will vacate and surrender possession of the
Terminated Space; (b) the agreed rentable area of the remainder of the Premises
will be 321,189; and (c) Tenant's parking rights under the Lease will be reduced
by two hundred seventy-eight (278) vehicles, Exhibit "A-4" attached to Amendment
#3 to Lease will be deemed deleted from the Lease and Exhibit "A-5" attached
hereto and incorporated herein (which shows a new parking plan for Tenant) will
be substituted in its place.  Despite the earlier termination of the Lease with
respect to the Terminated Space, and in addition to other rent payable under the
Lease, all rent that would have been payable by Tenant in connection with each
portion of the Terminated Space absent this termination will continue to be paid
as rent under the Lease through the first to occur of: April 30, 2001, or the
date that a new tenant under a new lease of that portion of the Terminated Space
occupies that portion of the Terminated Space to conduct business, or the rent
commencement date under any new lease of that portion of the Terminated Space.
(As a hypothetical example, if Offer Space #1, 29,916 s.f., is leased by
Landlord pursuant to a new lease with a rent commencement date of February 1,
2001, rent payable by Tenant for Offer Space #1 would be payable only through
January 31, 2001.)  In Section 27(e)(i) of the Lease, the figure "500,000 square
feet" will be deemed reduced to "407,300 square feet".  Following the effective
termination date of the Lease with respect to the Terminated Space, neither
party will have any further rights or obligations to the other with respect
thereto (except for any unpaid rent due under

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the Lease or hereunder for any period before the termination date with respect
to the Terminated Space).

     3.2  As of the effective termination date of the Lease with respect to the
applicable portion of the Terminated Space, Tenant's Percentage will be deemed
decreased as follows: Offer Space #1 - 3.18%; Fifth Expansion Space #1 - 1.51%;
Fifth Expansion Space #2 - 1.67%; and the Temporary Space - 3.50%.  Following
the effective  termination date of the Lease with respect to all of the
Terminated Space, Tenant's Percentage will be 34.15%, assuming that Tenant
leases no other space in the Project.

     3.3  As a material inducement to Landlord to enter into this Amendment,
Tenant agrees that, as of the date hereof, Landlord is not, to Tenant's
knowledge, in default under the Lease, and Tenant represents to Landlord that
Tenant has not subleased, assigned or conveyed the Terminated Space or its
interests therein to anyone else.

     3.4  As a material inducement to Tenant to enter into this Amendment,
Landlord agrees that, as of the date hereof, Tenant is not, to Landlord's
knowledge, in default under the Lease.

     Time is of the essence in this Amendment and holding over will not be
permitted.  Notwithstanding anything herein to the contrary, this Amendment will
not be binding on Landlord until and unless Landlord receives approval from its
current Landlord's Mortgagee.  Promptly after receiving such approval (or
disapproval, as the case may be) from its current Landlord's Mortgagee, Landlord
will notify Tenant of same in writing.  The Lease remains in full force and
effect, and except as set forth above, the Lease remains unchanged.

     IN WITNESS WHEREOF, intending to be legally bound, the parties have
executed this Amendment as of the date in Article 1 above.

CMGI, Inc., a Delaware corporation        Andover Mills Realty Limited
                                          Partnership, a Massachusetts limited
                                          partnership

By:  /s/ Andrew J. Hajducky, III          By:  Brickstone Square Realty, Inc., a
     Name:  Andrew J. Hajducky, III            Massachusetts corporation,
     Title: Chief Financial Officer            general partner
     Authorized Signature

                                               By:  /s/ Martin Spagat
                                                    Name:  Martin Spagat
                                                    Title: Vice President
                                                    Authorized Signature

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                                                                   EXHIBIT 10.21
                             AMENDMENT #6 TO LEASE
                             ---------------------

1.   Parties.
     -------

     This Amendment, dated as of April 17, 2001, is between Andover Mills Realty
Limited Partnership ("Landlord") and CMGI, Inc. ("Tenant").

2.   Recitals.
     --------

     2.1  Landlord and Tenant have entered into Lease, dated as of April 12,
1999, for space in Brickstone Square in Andover, Massachusetts (as now or
hereafter amended, the "Lease").  Unless otherwise defined, terms used in this
Amendment have the same meanings as those used in the Lease.

     2.2  Tenant wishes to grant to Landlord the right and option to terminate
the Lease with respect to Offer Space #2, consisting of 9,472 s.f. of agreed
rentable area on the 2nd Floor of Building 200.  The parties hope that Landlord
will be able to lease Offer Space #2 to others and then exercise this
termination option, although Landlord is not obligated either to lease or
exercise. Subject to the terms of this Amendment, if Landlord validly exercises
its option, Tenant will assign and transfer its interest in Offer Space #2 to
Landlord and the Lease will then terminate with respect to Offer Space #2 only.
In order to accomplish this and other matters, for $10.00 and other good and
valuable consideration, the receipt and sufficiency of which is acknowledged,
the parties agree and the Lease is amended as follows as of the date hereof,
notwithstanding anything to the contrary:

3.   Amendments.
     ----------

     3.1  Tenant hereby grants to Landlord the right and option to terminate the
Lease with respect to Offer Space #2 only.  Landlord has no obligation to
exercise this option, but if it elects to exercise it will do so by delivering a
written exercise notice to Tenant.

     3.2  As of the date that Landlord validly exercises this option, Tenant
will be deemed to have assigned, conveyed and transferred to Landlord all of
Tenant's right, title and interest in and to Offer Space #2, and: (a) the Lease
will terminate and expire as to Offer Space #2 only and Tenant and its
Affiliates will vacate and surrender possession of Offer Space #2; (b) the
agreed rentable area of the remainder of the Premises will be reduced by 9,472
s.f.; and (c) Tenant's parking rights under the Lease will be reduced by twenty-
eight (28) vehicles, Exhibit "A-5" attached to Amendment #5 to Lease will be
deemed deleted from the Lease and Exhibit "A-7" attached hereto and incorporated
herein (which shows a new parking plan for Tenant) will be substituted in its
place.  Despite the earlier termination of the Lease with respect to Offer Space
#2, and in addition to other rent payable under the Lease, all rent that would
have been payable by Tenant in connection with Offer Space #2 absent this
termination will continue to be paid as rent under the Lease through the date
(the "Initial Rent Termination Date") that is the first to occur of: ninety (90)
days after Landlord exercises this option; or the date that a new tenant under a
new lease of Offer Space #2 occupies Offer Space #2 to conduct business; or the
rent commencement date under any new lease of Offer Space #2.  After the Initial
Rent Termination Date, rent will terminate  entirely for 5,000 s.f. of Offer
Space #2, and for the next one (1) calendar year after the Initial Rent
Termination Date, Tenant will continue to pay only the rent that would have been
payable by Tenant in connection with Offer Space #2 absent this

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termination for the remainder of Offer Space #2 (i.e., on 4,472 s.f). Tenant
will not be required to pay any rent in connection with Offer Space #2 for any
period after this one (1)-year period. (As a hypothetical example, if Landlord
exercises this option and leases Offer Space #2 to a new tenant under a new
lease with a rent commencement date thirty (30) days after exercise, and no
earlier occupation by the new tenant, rent payable by Tenant in connection with
Offer Space #2 would continue for all of that space until thirty (30) days after
exercise [i.e., until the Initial Rent Termination Date], and it would continue
for only 4,472 s.f. of that space until one (1) year after that Initial Rent
Termination Date, after which it would terminate entirely.) In Section 27(e)(i)
of the Lease, the figure for the area set forth therein will be reduced by 9,472
s.f. Following Landlord's exercise of this option with respect to Offer Space
#2, neither party will have any further rights or obligations to the other with
respect thereto (except for any unpaid rent due under the Lease or hereunder for
any period before the rent is to terminate with respect to that portion of Offer
Space #2).

     3.3  Following the Rent Termination Date of the Lease with respect to all
of Offer Space #2, Tenant's Percentage will be reduced by 1.01%, to a total of
33.14%, assuming that Tenant leases no other space in the Project.

     3.4  As a material inducement to Landlord to enter into this Amendment,
Tenant agrees that, as of the date hereof, Landlord is not, to Tenant's
knowledge, in default under the Lease, and Tenant represents to Landlord that
Tenant has not subleased, assigned or conveyed Offer Space #2 or its interests
therein to anyone else.

     3.5  As a material inducement to Tenant to enter into this Amendment,
Landlord agrees that, as of the date hereof, Tenant is not, to Landlord's
knowledge, in default under the Lease.

     Time is of the essence in this Amendment and holding over will not be
permitted.  The Lease remains in full force and effect, and except as set forth
above, the Lease remains unchanged.

     IN WITNESS WHEREOF, intending to be legally bound, the parties have
executed this Amendment as of the date in Article 1 above.

CMGI, Inc., a Delaware corporation    Andover Mills Realty Limited
                                      Partnership, a Massachusetts limited
                                      partnership
By:  /s/ Andrew J. Hajducky III
     Name: Andrew J. Hajducky III     By:  Brickstone Square Realty, Inc., a
     Title: Chief Financial Officer        Massachusetts corporation, general
     Authorized Signature                  partner

                                           By:  /s/ Martin Spagat
                                                Name: Martin Spagat
                                                Title: Vice President
                                                Authorized Signature

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