Document:

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                                                                   Exhibit 10.58

                                                          CONFIDENTIAL

                      Addendum No. 1 to Market Agreement

     This Addendum No. 1 to Market Agreement (this "Addendum") is made as of
August 1, 2000 (the "Effective Date") by and between Stamps.com Inc., a Delaware
corporation with offices at 3420 Ocean Park Boulevard, Suite 1040, Santa Monica,
California 90405 ("Client") and Cydcor Limited, an Ontario corporation with
offices at 155 Gordon Baker Road, Suite 212, Willowdale, Ontario, M2H 3N5
("Manager").

     WHEREAS, the parties have entered into a Market Agreement dated as of May
15, 2000 (the "Agreement"); and

     WHEREAS, the parties wish to modify and supplement the provisions of such
Agreement.

     NOW, THEREFORE, in consideration of the mutual promises set forth below,
the parties agree as follows:

     1.   Pursuant to Section 8 of the Agreement, the parties agree to extend
the Agreement for an additional period of two (2) years from the Effective Date
of this Addendum (the "New Term").

     2.   During the New Term, the Payment Schedule attached hereto as Exhibit A
                                                                       ---------
shall apply:

     3.   As additional consideration for Manager's commitments hereunder,
Client shall deliver to Manager as of the Effective Date of this Addendum, a
Warrant Issuance Agreement substantially in the form attached hereto as
Exhibit B.
---------

     4.   Capitalized terms used but not defined herein shall have the meaning
given them in the Agreement.

     5.   Except as expressly set forth herein, the terms and conditions of the
Agreement shall continue in full force and effect.

     6.   This Addendum may be executed in one or more counterparts, each of
which when executed shall be deemed to be an original but all of which taken
together shall constitute one and the same instrument.

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     7.   In the event of a conflict between the Agreement and this Addendum,
the terms and conditions of this Addendum shall control.

     IN WITNESS WHEREOF, the parties have caused their duly authorized
representatives to enter into this Addendum, effective as of the Effective Date.

Cydcor Limited                               Stamps.com Inc.

By: /s/ Avie Roth                            By: /s/ Douglas Walner
    ----------------------                       --------------------

Name:  Avie Roth                             Name: Douglas Walner
     ---------------------                       --------------------

Title: Vice President                        Title: SVP, GM
     ---------------------                       --------------------

                                      -2-
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                                   EXHIBIT A

                               PAYMENT SCHEDULE

                                     *****

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[*] Confidential information has been omitted and separately filed with the
    Securities and Exchange Commission. Confidential treatment has been
    requested with respect to the omitted portions.

                                      -3-
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                                   EXHIBIT B<PAGE>

                                                                   EXHIBIT 10.59

                                STAMPS.COM INC.
                       3420 Ocean Park Blvd., Suite 1040
                        Santa Monica, California 90405

February 13, 2001

Mr. John M. Payne
660 Thalia Street
Laguna Beach, California 92651

Dear John:

     The following confirms our mutual agreement to amend the terms of your
December 20, 2000 separation letter (the "Separation Letter") with Stamps.com
Inc. (the "Company"):

     1.   Upon receipt of this amendment letter signed and dated by you, the
Company agrees to pay you a lump sum amount of $120,807.37, which amount
represents 90% of remaining payments to which you would otherwise be entitled to
under paragraph 2(a) of the Separation Letter.  Amounts paid under this
amendment letter shall be less any and all appropriate withholding taxes.

     2.   You acknowledge that by payment of the amounts set forth above, the
Company shall have no further payment obligations to you and you shall be
entitled to no further payments under paragraph 2(a) of the Separation Letter.

     3.   Except as expressly amended by this amendment letter, the terms,
releases, covenants and agreements contained in the Separation Letter remain
unaffected by this amendment letter and continue in full force and effect.

     4.   The Separation Letter (including Exhibits A through D thereto) and
this amendment letter constitute the entire agreement between you and the
Company concerning the terms of your employment severance and the compensation
related thereto.  No amendments to the Separation Letter or this amendment
letter will be valid unless written and signed by you and an officer of the
Company.

     I believe this letter fully describes our agreement, and if you are in
accord, please sign and date below.  We wish you the best in your future
endeavors.

                              Sincerely yours,

                               /s/ KEN McBRIDE
                              _________________________________
                              Ken McBride
                              Chief Financial Officer

     I agree to and accept the terms of this letter.

     /s/ John M. Payne                     February 17, 2001
     _______________________________       ____________________
     John M. Payne                         Date<PAGE>

                                                                   EXHIBIT 10.60
                              September 22, 2000

                              [LOGO APPEARS HERE]

Mr. Loren Smith
P.O. Box 953
El Prado, NM  87529-0953

Dear Loren:

     In October 1999, at the request of the Board of Directors, you agreed to
serve as President and Chief Operating Officer of Stamps.com Inc. (the
"Company"), which agreement was documented in an offer letter dated October 20,
1999.   You and the Board have subsequently agreed that the business needs you
were requested to fulfill have largely been addressed and that as of the end of
September you have decided to resign your position as a senior manager of the
Company.  This letter sets forth the arrangements for your transition from a
senior executive role at the Company and confirms our mutual agreement as
follows:

     1.   The Company agrees to accept your resignation from the offices of
President and Chief Operating Officer, effective September 30, 2000.  You agree
to remain in your current role as a member of the Company's Board of Directors.

     2.   Upon receipt of this letter signed and dated by you and the expiration
of the time periods in paragraphs 12 and 13, the Company agrees to:

          (a)  Pay you the amount of $10,416.66 semi-monthly for the payroll
               periods covering October 1, 2000 through March 31, 2001, less all
               appropriate withholding taxes.

          (b)  Pay you a lump sum amount of $66,000, less all appropriate
               withholding taxes. Such amount shall be paid to you on the first
               payroll period following your execution of this letter.

          (c)  Allow you continued use of the cell phone and cell phone account
               provided to you by the Company until December 31, 2000; provided,
               however, that the Company will only pay for reasonable and
               necessary charges incurred on behalf of the Company. After
               December 31, 2000, your cell phone account will be closed;
               however, you may keep the cell phone for your personal use.
<PAGE>

          (d)  Allow you to keep the laptop computer and Palm Pilot provided to
               you by the Company for your personal use.

          (e)  Grant you an option to purchase 2,500 shares of the Company's
               Common Stock, which option shall be immediately exercisable and
               shall have an exercise price equal to the closing price of the
               Company's Common Stock on Nasdaq on September 29, 2000. The
               option shall have a term of 10 years; provided, however, that the
               option shall cease to be exercisable at such time as you are no
               longer a member of the Company's board of directors.

          (f)  Pay you for any accrued and unused vacation and reimburse you for
               any unpaid expenses incurred and identified on expense
               reimbursement forms previously submitted by you and approved for
               payment by the Company's Chief Financial Officer and Controller.

          (g)  Pay for the shipment to Taos, New Mexico of personal effects and
               items located in your temporary living space and office in Santa
               Monica.

     3.   You acknowledge that by payment of the amounts set forth above, you
will receive all money and other benefits due you as a result of your employment
with and discontinuation of your executive role with the Company.

     4.   This arrangement shall not modify the terms of your stock options
granted in February 1999 for your appointment as a director (108,000 shares) and
as a consultant (135,000 shares) to the Company.

     5.   Under the terms of the Company's 1999 Stock Incentive Plan, you
acknowledge that you will have until November 30, 2000 to exercise any options
that you received upon your appointment as the Company's President and Chief
Operating Officer in October 1999 and that are vested as of September 30, 2000.
As of September 30, 2000 and with respect to options granted upon your
appointment as the Company's President and Chief Operating Officer, you will
have vested in options to purchase 137,500 shares of Common Stock with an
exercise price of $35.63.
<PAGE>

     6.   You agree to speak on the Company's behalf at the E-Post World
Conference to be held from September 18-20, 2000 in Miami, Florida. All travel
expenses incurred by you for this appearance (and any other public appearances
agreed to between you and the Company's Chief Executive Officer) shall be
reimbursed in accordance with the Company's travel reimbursement policy.

     7.   You agree to return to the Company all other property purchased or
leased on your behalf by October 31, 2000. In lieu of returning any leased
property, you may terminate your lease or assume any lease that is not already
leased in your name.

     8.   You fully release and discharge the Company, all affiliated
corporations, past and present officers, directors, employees, agents and
representatives, and each of them of and from, without limitation, any and all
rights, claims, liabilities, losses or expenses of any kind whether arising out
of, from, or related to your employment relationship with the Company, your
resignation thereof, or arising out of any other matter between you and the
Company, and specifically including any claim of age discrimination under the
Age Discrimination in Employment Act, as amended, and the California Fair
Employment & Housing Act.

     9.   You understand and agree that the claims released hereby are intended
to and do include any and all claims of every nature and kind whatsoever, known
or unknown, suspected or unsuspected, which you have or may have against the
Company and you hereby waive any and all rights you have or may have under
Section 1542 of the California Civil Code.  Section 1542 provides as follows:

               A general release does not extend to claims which the creditor
               does not know or suspect to exist in his favor at the time of
               executing the release, which if known by him must have materially
               affected his settlement with the debtor.

     10.  You agree not to directly or indirectly disparage the Company, its
officers or employees in any manner, or directly or indirectly solicit or
attempt to solicit its employees or customers.  In addition, you agree that you
remain bound by the Confidential Information and Inventions Assignment Agreement
that you signed on October 20, 1999.  You also represent and warrant that you
have complied with your
<PAGE>

obligations under that confidentiality agreement and that you will continue to
comply with such obligations. You and the Company agree that any public
statements by you or the Company regarding your departure shall be mutually
agreed upon prior to release and that such public statements must be made at
such time as the Company's corporate counsel advises is appropriate for SEC
reporting purposes.

     11.  You acknowledge that you have been advised to consult with an attorney
before signing this agreement, and that you have voluntarily and knowingly
executed this agreement after having had the opportunity to consult with an
attorney.

     12.  You further acknowledge that you may consider the terms of this
agreement for 21 days before signing it, and that you have been so advised.
This agreement was provided to you on September 22, 2000.  Accordingly, you have
until October 13, 2000 to decide whether you will sign the agreement.

     13.  For a period of seven days following your execution of this agreement,
you may revoke the agreement, and the agreement shall not become effective or
enforceable until the revocation period has expired.

     14.  This letter constitutes the entire agreement between you and the
Company concerning the terms of your employment severance and the compensation
related thereto.  No amendments to this agreement will be valid unless written
and signed by you and an officer of the Company.

     I believe this letter fully describes our agreement, and if you are in
accord, please sign and date below.  We wish you the best in your future
endeavors.

                         Sincerely yours,

                          /s/ John W. LaValle
                         --------------------------
                         John W. LaValle
                         Executive Vice President and Chief Financial Officer

     I agree to and accept the
     terms of this letter.

     /s/ Loren E. Smith                  26 September '00
     -----------------------            ---------------------
     Loren E. Smith                     Date

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