Document:

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                                                                   Exhibit 10.51

                         CONSULTING SERVICES AGREEMENT

     The following confirms the agreement between JOHN M. PAYNE (the
"Consultant") and STAMPS.COM INC., (the "Company"), with respect to consulting
services to the Company:

1.  Definitions.
    -----------

     a.  "Company Materials" shall have the meaning ascribed to it in that
certain Confidential Information and Invention Assignment Agreement between
Consultant and the Company dated even date herewith.

     b.  "Confidential Information" shall have the meaning ascribed to it in
that certain Confidential Information and Invention Assignment Agreement between
Consultant and the Company dated even date herewith.

     c.  "Services" means the consulting services provided by the Consultant to
the Company during the term of this Agreement.  The Services may include,
without limitation, strategic planning and business development advice requested
by the Company and agreed to by Consultant, subject to Consultant's
availability.

2.   Confidential Information.  All Confidential Information and results of the
     ------------------------
Services are the sole property of the Company.  Consultant hereby assigns to the
Company any rights Consultant may have or acquire in such Confidential
Information or results.  As required by the Confidential Information and
Invention Assignment Agreement between Consultant and the Company dated even
date herewith, Consultant will keep in confidence and trust and will not use or
disclose any Confidential Information.

3.   Company Materials.  All Company Materials are the sole property of the
     -----------------
Company.  Consultant agrees that during the term of this Agreement, Consultant
will not remove any Company Materials from the business premises of the Company
or deliver any Company Materials to any third party except as may be necessary
and appropriate in the ordinary course of performing the Services.  Consultant
further agrees that upon the Company's request and in any event upon completion
of the Services, Consultant shall deliver to the Company all Company Materials
and results of the Services.  At all times before or after completion of the
Services, the Company shall immediately have the right to examine the results of
the Services and any materials relating there to ensure Consultant's compliance
with the provisions of this Agreement.

4.   Consulting Services.
     -------------------

     a.  This Agreement will terminate on June 30, 2001, unless earlier
terminated pursuant to Section 6 of this Agreement.

     b.  Consultant agrees to render the Services to the Company for the term of
this Agreement. The parties acknowledge and agree that any request for Services
and the scope of any Services shall be agreed to in a written scope of work
executed by both parties prior to the commencement of a project.  Consultant
agrees to promptly submit all results of the Services to the Company, in written
form or other tangible form, as may be agreed in a written scope of work
executed by both parties.

     c.  The Company shall pay Consultant an amount of $2,000 per day for any
Services that Consultant and the Company agree in writing to be performed
hereunder.  In addition, the Company shall
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reimburse Consultant for reasonable long distance travel (transportation,
lodging and meals) and telephone expenses Consultant is required to incur in
providing the Services; provided, however, that such expenses shall be approved
in advance by the Company.

     d.  Upon completion of any projects, Consultant shall provide the Company
with invoices detailing the consulting time, fees and expense reimbursements
that Consultant believes are due under this Agreement, and shall itemize and
provide receipts for expenses upon request. The Company agrees to pay approved
invoices upon receipt.

5.   Noncompetition.  Consultant agrees that, during the term of this Agreement,
     --------------
Consultant will not engage in any employment, business, or activity that is in
any way competitive with the business or reasonably anticipated business of the
Company or EncrypTix, Inc., and Consultant will not assist any other person or
organization in competing with or in preparing to compete with the Company or
EncrypTix, Inc.

6.   Early Termination.  In the event a party is in breach of any
     -----------------
representation, warranty or covenant of Consultant's Separation Letter with the
Company dated even date herewith, the other party may immediately terminate this
Agreement upon written notice to the first party.

7.   Independent Contractor; Taxes.  Consultant is an independent contractor and
     -----------------------------
is solely responsible for all taxes, withholdings, and other similar statutory
obligations, including, but not limited to, Workers' Compensation Insurance; and
Consultant agrees to defend, indemnify and hold Company harmless from any and
all claims made by any entity on account of an alleged failure by Consultant to
satisfy any such tax or withholding obligations.

8.   No Agency.  Consultant has no authority to act on behalf of or to enter
     ---------
into any contract, incur any liability or make any representation on behalf of
the Company.

9.   Survival.  Consultant agrees that Sections 1 through 3 and Sections 7
     --------
through 13 of this Agreement shall survive any termination of this Agreement,
and that the Company is entitled to communicate Consultant's obligations under
this Agreement to any future client or potential client of Consultant.

10.  Choice of Law; Severability.  This Agreement shall be construed in
     ---------------------------
accordance with the laws of the State of California without regard to the
conflict of laws provisions thereof.  If any provision of this Agreement is held
to be illegal or unenforceable, such provision shall be limited or excluded from
this Agreement to the minimum extent required so that this Agreement shall
otherwise remain in full force and effect and enforceable in accordance with its
terms.

11.  Successors and Assigns; Assignment.  This Agreement shall be binding upon
     ----------------------------------
Consultant and the Company, and inure to the benefit of, the parties hereto and
their respective heirs, successors, assigns, and personal representatives;
provided, however, that it shall not be assignable by Consultant.

12.  Entire Agreement.  With the exception of the Separation Letter between the
     ----------------
Consultant and the Company dated even date herewith and the exhibits thereto,
this Agreement contains the entire understanding of the parties regarding its
subject matter and can only be modified by a subsequent written agreement
executed by the parties.

13.  Notices.  All notices required under this Agreement shall be addressed to
     -------
the address set forth below (or at such other address as may be provided by
written notice given in accordance with this Section 13) and provided by (i)
registered mail, return receipt requested; or (ii) facsimile, with a

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confirmation copy as provided in clause (i), (iii) or (iv) of this Section 13;
or (iii) a courier service with tracking capabilities; or (iv) hand delivery.

Dated:  December 20, 2000

Accepted and Agreed to:

STAMPS.COM INC.                              JOHN M. PAYNE

By:____________________________________      _________________________________
                                             Consultant Signature
Name:__________________________________

Title:_________________________________

                                       3<PAGE>

                                                                   Exhibit 10.52

                                STAMPS.COM INC.

                         CONFIDENTIAL INFORMATION AND
                        INVENTION ASSIGNMENT AGREEMENT

                               DECEMBER 20, 2000

     As a condition of my separation from employment and retention as a
consultant by Stamps.com Inc., a Delaware corporation, or any of its current or
future subsidiaries, affiliates, successors or assigns (collectively, the
"Company"), and in consideration of my separation from employment and entry into
--------
a consulting relationship with the Company and my receipt of the compensation
now and hereafter paid to me by the Company, I agree to the following:

     1.   Employment or Consulting Relationship.  I understand and acknowledge
          -------------------------------------
that this Agreement does not create an employment relationship with the Company.
I understand and acknowledge that this Agreement does not alter, amend or expand
upon any rights I may have to continue in a consulting relationship with, or the
duration of my consulting relationship with, the Company under any agreements
between the Company and me or under applicable law.  The consulting relationship
between the Company and me that commences upon the date of this Agreement and is
evidenced by a consulting agreement dated even date herewith shall be referred
to herein as the "Relationship."
                  ------------

     2.   Confidential Information.
          ------------------------

          (a)  Company Information.  I agree at all times during the term of my
               -------------------
Relationship with the Company and thereafter, to hold in strictest confidence,
and not to use, except for the benefit of the Company, or to disclose to any
person, firm, corporation or other entity without written authorization of the
Board of Directors of the Company, any Confidential Information of the Company
which I obtain or create or any Confidential Information of the Company which I
obtained or created on or after May 30, 1998. I further agree not to make copies
of such Confidential Information except as authorized by the Company. I
understand that "Confidential Information" means any Company proprietary
                 -------------------------
information, technical data, trade secrets or know-how, including, but not
limited to, research, products, services, suppliers, customer lists and
customers (including, but not limited to, customers of the Company on whom I
called or with whom I became acquainted since May 30, 1998), prices and costs,
markets, software, algorithms, ideas, compositions, techniques, improvements,
inventions (whether patentable or not), works of authorship, derivative works,
business and product development plans, the salaries and terms of compensation
of other employees, developments, laboratory notebooks, processes, formulas,
technology, designs, drawings, engineering, hardware configuration information,
marketing, licenses, finances, budgets or other business information concerning
the Company's actual or anticipated business, research or development that was
or is disclosed to me by the Company either directly or indirectly in writing,
orally or by drawings or observation of parts or equipment or created by me
during the period of the Relationship and during the term of my employment,
directorship or previous consultancy, whether or not during working hours. I
understand that "Confidential Information" includes, but is not limited to,
                 ------------------------
information pertaining to any aspects of the Company's business which is either
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information not known by actual or potential competitors of the Company or is
proprietary information of the Company or its customers or suppliers, whether of
a technical nature or otherwise. I further understand that Confidential
Information does not include any of the foregoing items which has become
publicly and widely known and made generally available through no wrongful act
of mine or of others who were under confidentiality obligations as to the item
or items involved.

     (b)  Company Materials. I understand that the Company possesses or will
          -----------------
possess "Company Materials" that are important to its business. For purposes of
         -----------------
this Agreement, "Company Materials" are documents or other media or tangible
                 -----------------
items that contain or embody Confidential Information or any other information
concerning the business, operations or plans of the Company, whether such
documents have been prepared by me or by others. "Company Materials" include,
                                                  -----------------
but are not limited to, blueprints, drawings, photographs, charts, graphs,
notebooks, customer lists, computer software (whether in the form of executable
code, data or any other form and in any format or structure whatsoever),
computer media, printouts, sound recordings and other printed, typewritten or
handwritten documents, as well as samples, prototypes, models, products and the
like.

          (c) Third Party Information.  I recognize that the Company has
              -----------------------
received and in the future will receive confidential or proprietary information
from third parties subject to a duty on the Company's part to maintain the
confidentiality of such information and to use it only for certain limited
purposes.  I agree to hold all such confidential or proprietary information in
the strictest confidence and not to disclose it to any person, firm or
corporation or to use it except as necessary in carrying out my work for the
Company consistent with the Company's agreement with such third party.

     3.   Inventions.
          ----------

          (a)  Inventions Retained and Licensed.  I have attached hereto, as
               --------------------------------
Exhibit A, a list describing with particularity all inventions, original works
---------
of authorship, developments, improvements, and trade secrets which were made by
me prior to May 30, 1998 (collectively referred to as "Prior Inventions"), which
                                                       ----------------
belong solely to me or belong to me jointly with another, which relate in any
way to any of the Company's proposed businesses, products or research and
development, and which are not assigned to the Company hereunder; or, if no such
list is attached, I represent that there are no such Prior Inventions.  If, in
the course of my Relationship with the Company, I incorporate into a Company
product, process or machine a Prior Invention owned by me or in which I have an
interest, the Company is hereby granted and shall have a non-exclusive, royalty-
free, irrevocable, perpetual, worldwide license (with the right to sublicense)
to make, have made, copy, modify, make derivative works of, use, sell and
otherwise distribute such Prior Invention as part of or in connection with such
product, process or machine.

          (b)  Assignment of Inventions.  I agree that I will promptly make full
               ------------------------
written disclosure to the Company, will hold in trust for the sole right and
benefit of the Company, and hereby assign to the Company, or its designee, all
my right, title and interest throughout the world in and to any and all
inventions, original works of authorship, derivative works, technology,
software, application programming interfaces, compositions, ideas, designs,
processes, techniques, data, developments, concepts, know-how, improvements or
trade secrets, whether or not patentable or registrable under copyright or
similar laws, which I have solely or jointly conceived or developed or reduced
to practice, or may solely or jointly cause to be conceived or developed or
reduced to practice, during the period beginning May 30, 1998 and ending upon
the termination of my Relationship with the Company (collectively referred to as
"Inventions"), except as provided in Section 3(d) below.  I further acknowledge
 ----------
that all Inventions made by me (solely or jointly with others) within the scope
of and

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during the period of beginning May 30, 1998 or during the Relationship are
"works made for hire" (to the greatest extent permitted by applicable law) and
 -------------------
were compensated by my salary (in the case of my employment) or by such amounts
paid to me under any applicable consulting agreement or consulting arrangements
(if I am or was a consultant), unless regulated otherwise by the mandatory law
of the state of California.

          (c)  Patent and Copyright Rights.  I agree to assist the Company, or
               ---------------------------
its designee, at the Company's expense, in every proper way to secure the
Company's rights in the Inventions and any copyrights, patents, trademarks, mask
work rights, moral rights, or other intellectual property rights relating
thereto in any and all countries, including the disclosure to the Company of all
pertinent information and data with respect thereto, the execution of all
applications, specifications, oaths, assignments, recordations, and all other
instruments which the Company shall deem necessary in order to apply for,
obtain, maintain and transfer such rights and in order to assign and convey to
the Company, its successors, assigns and nominees the sole and exclusive rights,
title and interest in and to such Inventions, and any copyrights, patents, mask
work rights, moral rights or other intellectual property rights relating
thereto.  I further agree that my obligation to execute or cause to be executed,
when it is in my power to do so, any such instrument or papers shall continue
after the termination of this Agreement until the expiration of the last such
intellectual property right to expire in any country of the world.  If the
Company is unable because of my mental or physical incapacity or unavailability
or for any other reason to secure my signature to apply for or to pursue any
application for any United States or foreign patents or copyright registrations
covering Inventions or original works of authorship assigned to the Company as
above, then I hereby irrevocably designate and appoint the Company and its duly
authorized officers and agents as my agent and attorney in fact, to act for and
in my behalf and stead to execute and file any such applications and to do all
other lawfully permitted acts to further the application for, prosecution,
issuance, maintenance or transfer of letters patent or copyright registrations
thereon with the same legal force and effect as if originally executed by me.  I
hereby waive and irrevocably quitclaim to the Company any and all claims, of any
nature whatsoever, which I now or hereafter have for infringement of any and all
proprietary rights assigned to the Company.

          (d)  Exception to Assignments.  I understand that the provisions of
               ------------------------
this Agreement requiring assignment of Inventions to the Company do not apply to
any invention which qualifies fully under the provisions of California Labor
Code Section 2870 (attached hereto as Exhibit B).  I will advise the Company
                                      ---------
promptly in writing of any inventions that I believe meet such provisions and
are not otherwise disclosed on Exhibit A.
                               ---------

     4.   Returning Company Documents.  I agree that, at the time of termination
          ---------------------------
of my Relationship with the Company, I will deliver to the Company (and will not
keep in my possession, recreate or deliver to anyone else) any and all Company
Materials, including but not limited to, devices, records, data, notes, reports,
proposals, lists, correspondence, specifications, drawings, blueprints,
sketches, laboratory notebooks, materials, flow charts, equipment, other
documents or property, or reproductions of any aforementioned items developed by
me pursuant to the Relationship or otherwise belonging to the Company, its
successors or assigns.  I also recognize and agree that I have no expectation of
privacy with respect to the Company's telecommunications, networking, or
information processing systems (including, without limitation, stored computer
files, e-mail messages and voice messages) and that my activity, and any files
or messages, on or using any of those systems may be monitored at any time
without notice.

     5.   Notification to Other Parties.  I hereby grant consent to notification
          -----------------------------
by the Company to any other parties besides the Company with whom I maintain an
employment or consulting relationship,

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including parties with whom such relationship commences after the effective date
of this Agreement, about my rights and obligations under this Agreement.

     6.   Solicitation of Employees, Consultants and Other Parties. I agree that
          --------------------------------------------------------
during the term of my Relationship with the Company, and for a period of twenty-
four (24) months immediately following the termination of my Relationship with
the Company, I shall not either directly or indirectly solicit, induce, recruit
or encourage any of the Company's employees or consultants to terminate their
relationship with the Company, or take away such employees or consultants, or
attempt to solicit, induce, recruit, encourage or take away employees or
consultants of the Company, either for myself or for any other person or entity.
Further, for a period of twenty-four (24) months following termination of my
Relationship with the Company for any reason, with or without cause, I shall not
solicit any licensor to or customer of the Company or licensee of the Company's
products, in each case, that are known to me, with respect to any business,
products or services that are competitive to the products or services offered by
the Company or under development as of the date of termination of my
Relationship with the Company.

     7.   Representations and Covenants.
          -----------------------------

          (a)  Facilitation of Agreement. I agree to execute promptly any proper
               -------------------------
oath or verify any proper document required to carry out the terms of this
Agreement upon the Company's written request to do so.

          (b)  Voluntary Execution. I certify and acknowledge that I have
               -------------------
carefully read all of the provisions of this Agreement and that I understand and
will fully and faithfully comply with such provisions.

     8.   Term of Obligations.  I agree that my obligations under this Agreement
          -------------------
shall continue in effect after termination of my Relationship with the Company,
regardless of the reason or reasons for termination, and whether such
termination is voluntary or involuntary on my part.

     9.   General Provisions.
          ------------------

          (a)  Governing Law.  The validity, interpretation, construction and
               -------------
performance of this Agreement shall be governed by the laws of the State of
California, without giving effect to the principles of conflict of laws.

          (b)  Entire Agreement.  With the exception of the Separation Letter
               ----------------
between me and the Company dated even date herewith and the exhibits thereto,
this Agreement sets forth the entire agreement and understanding between the
Company and me relating to the subject matter herein and merges all prior
discussions between us.  No modification or amendment to this Agreement, nor any
waiver of any rights under this Agreement, will be effective unless modified by
a subsequent written agreement executed by an authorized officer of the Company.
Any subsequent change or changes in my duties, obligations, rights or
compensation will not affect the validity or scope of this Agreement.

          (c)  Severability.  If one or more of the provisions in this Agreement
               ------------
are deemed void by law, then the remaining provisions will continue in full
force and effect.

          (d)  Successors and Assigns.  This Agreement will be binding upon my
               ----------------------
heirs, executors, administrators and other legal representatives and will be for
the benefit of the Company, its successors, and its assigns.

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<PAGE>

          (e)  Survival.  The provisions of this Agreement shall survive the
               --------
termination of the Relationship and the assignment of this Agreement by the
Company to any successor in interest or other assignee.

          (f)  ADVICE OF COUNSEL.  I ACKNOWLEDGE THAT, IN EXECUTING THIS
               -----------------
AGREEMENT, I HAVE HAD THE OPPORTUNITY TO SEEK THE ADVICE OF INDEPENDENT LEGAL
COUNSEL, AND I HAVE READ AND UNDERSTOOD ALL OF THE TERMS AND PROVISIONS OF THIS
AGREEMENT.  THIS AGREEMENT SHALL NOT BE CONSTRUED AGAINST ANY PARTY BY REASON OF
THE DRAFTING OR PREPARATION HEREOF.

The parties have executed this Agreement as of December 20, 2000.

COMPANY:                                     JOHN M. PAYNE:

STAMPS.COM INC.

_________________________________        _______________________________________
Signature                                Signature

By: _____________________________        _______________________________________
                                         Printed Name
Title: __________________________

Address: 3420 Ocean Park Blvd.           Address: 660 Thalia Street
         Suite 1040                               Laguna Beach, California 92651
         Santa Monica, CA 90405

                                       5
<PAGE>

                                   EXHIBIT A
                                   ---------

                            LIST OF PRIOR INVENTIONS
                        AND ORIGINAL WORKS OF AUTHORSHIP
                            EXCLUDED FROM SECTION 4

VIDO - Voice In Data Out - A system and method for using voice command/control
to a device and voice narration through to a switch to control transmission of
data wirelessly to handheld telephone devices.

Trademark Application - Vocal Rain

Trademark Application - SimpleAir

___ No inventions or improvements

___ Additional Sheets Attached

Signature:__________________________

Print Name:_________________________

Date:_______________________________
<PAGE>

                                   EXHIBIT B
                                   ---------

Section 2870 of the California Labor Code is as follows:

     (a)  Any provision in an employment agreement which provides that an
employee shall assign, or offer to assign, any of his or her rights in an
invention to his or her employer shall not apply to an invention that the
employee developed entirely on his or her own time without using the employer's
equipment, supplies, facilities, or trade secret information except for those
inventions that either:

          (1)  Relate at the time of conception or reduction to practice of the
invention to the employer's business, or actual or demonstrably anticipated
research or development of the employer; or

          (2)  Result from any work performed by the employee for the employer.

     (b)  To the extent a provision in an employment agreement purports to
require an employee to assign an invention otherwise excluded from being
required to be assigned under subdivision (a), the provision is against the
public policy of this state and is unenforceable.

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