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                                                                   EXHIBIT 10.12

                  [LETTERHEAD OF MEDIAPLEX INC. APPEARS HERE]

                                 March 7, 2000

VIA TELEFAX:  650-321-1387
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Mr. Michael Stanek
Four Altree Court
Atherton, CA 94027

     Re:  Terms of Employment Offer with Mediaplex, Inc.
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Dear Michael:

     Mediaplex, Inc, (the "Company"), is pleased to offer you the position
described below.  This letter sets forth the terms and conditions of your
employment with the Company.

I.   Description of Employment Position and Responsibilities. You will serve in
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     the position of Chief Financial Officer. By executing this agreement, you
     agree to assume and discharge such duties and responsibilities as are
     commensurate with this position and such other duties and responsibilities
     that are assigned to you from time to time by the Company's Board of
     Directors, Chief Executive Officer, or your then supervisor. During the
     term of your employment, you shall devote your full time, skill and
     attention to your duties and responsibilities and shall perform them
     faithfully, diligently and competently. In addition, you shall comply with
     and be bound by the operating policies, procedures and practices of the
     Company in effect from time to time during your employment.

II.  Employment Considerations.
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     2.1  At-Will Employment.  You acknowledge that your employment with the
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     Company is for an unspecified duration that constitutes at-will employment,
     and that either you or the Company can terminate this relationship at any
     time, with or without cause and without notice.

     2.2  Employment Eligibility.  Your employment is contingent on your
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     submission to the Company of satisfactory original documentation to verify
     your identity and eligibility for employment in the United States.
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Mr. Michael Stanek                                                      [LOGO]
March 7, 2000
Page 2 of 6


III.  Compensation.
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      3.1  Base Salary. In consideration of your services, effective March 8,
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      2000, you will be paid an annual base salary of $250,000 (Two Hundred and
      Fifty Thousand Dollars and no Cents), payable no less frequently than on a
      monthly basis in accordance with the Company's standard payroll practices.
      Your base salary, in conjunction with your performance evaluation, is
      normally reviewed annually by the appropriate management of the Company.

      3.2  Incentive Compensation. In addition to your base salary, you may be
           ----------------------
      entitled to participate in such incentive compensation plan that may be
      adopted by the Company in its sole discretion. You understand that the
      adoption of any such plan, the eligibility and measurement criteria and
      all other terms shall be at the sole discretion of the Company. You will
      be eligible to receive a bonus of up to 15% (Fifteen Percent) of your Base
      Salary upon the achievement of certain milestones to be established by
      your supervisor within thirty (30) days of your date of commencement with
      the Company.

      3.3  Forgiveable Loan. In addition to the Base Salary and Incentive
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      Compensation described above, upon the earlier of the successful
      completion of the proposed follow-on offering or the expiration of forty-
      five (45) days from your commencement of employment with the Company, you
      shall receive from the Company a one-time loan in the amount of One
      Million Dollars ($1 million). This loan shall be forgiven upon the
      expiration of four (4) years from the date of the commencement of your
      employment under this Agreement. Provided however, in the event your
      employment is terminated for Cause as defined herein, or you voluntarily
      terminate your employment, you shall be responsible to pay the Company the
      remaining balance of the loan at the time of your termination, including
      interest on the remaining principal at the reasonable fixed commercial
      rate of six percent (6.0%).

      3.4. Termination for Other Than Cause. In the event that the Company
           --------------------------------
      elects to terminate you for other than "Cause" (as defined below), you
      will be entitled to receive two (2) weeks of compensation for every four
      (4) weeks you were employed at the Company up to a maximum amount of six
      (6) months of paid salary. This severance may be paid after termination by
      the Company in its sole discretion in one lump sum or every two-weeks
      until paid off in its entirety. Additionally, in the event that the
      Company elects to terminate you for other than "Cause", you shall be
      entitled to receive any compensation or benefits due to you under your
      Stock Option Agreement, which shall be sent to you separately. Termination
      pursuant to this Section does not prejudice any other remedy to which the
      terminating party may be entitled at law, in equity or under this
      Agreement. This is the only termination agreement between the Company and
      you, and the parties acknowledge that this Agreement supersedes and
      replaces and other written or oral agreement, representation, or
      understanding between the parties concerning termination and that this
      Agreement can only be modified in a writing signed by the Company's Chief
      Executive Officer or an officer authorized and instructed to do so by the
      Board of Directors.
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Mr. Michael Stanek                                                      [LOGO]
March 7, 2000
Page 3 of 6


     3.5  Termination for Cause.   In the event that your employment with the
          ---------------------
     Company is terminated for "Cause" (as defined below), you shall not be
     entitled to receive any severance benefits, including, without limitation,
     those benefits described in paragraph 3.4 above, or other compensation by
     the Company, except as to that portion of any unpaid salary, incentive
     bonus and other benefits earned by you up to and including the effective
     date of such termination and the ability to exercise the vested portion of
     your options in accordance with the terms of your Stock Option Agreement.

     3.6  "Cause" Defined.   "Cause" shall mean any one of the following: (i)
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     your conviction of (or plea of guilty or nolo contendere to) a felony which
     the Board of Directors reasonably believes had or will have a material
     detrimental effect on the Company's reputation or business, (ii) a grossly
     negligent or willful act by you which constitutes gross misconduct and
     which is injurious to the Company, or (iii) continued violations by you of
     your material duties which are demonstrably willful or grossly negligent or
     a willful disregard for lawful directives of the Chief Executive Officer or
     the Board of Directors on your part forty five (45) days after there has
     been delivered to you a written demand for performance from the Company
     which describes the basis for the Company's belief that have not
     substantially performed your duties.

     3.7  Death or Disability. Your death or permanent disability while employed
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     under this agreement will be treated as termination of employment by the
     Company without Cause in accordance with Section 3.3 above; provided,
     however, that the vesting acceleration under your Option Agreement shall be
     limited to the greater of (i) 150,000 shares or (ii) the number of shares
     actually vested as of such termination.

     3.8  Voluntary Termination. In the event that you terminate your employment
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     with the Company of your own volition and not as a result of circumstances
     described in Section 3.6 above, such termination will have the same
     consequences as a termination for Cause under Section 3.4 above.

IV.  Additional Benefits.
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     4.1  Health Insurance/Vacation/Benefit Plans.  You will be entitled to
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     receive the standard employee benefits made available by the Company to its
     employees to the full extent of your eligibility therefor.  You shall be
     entitled to three (3) weeks of paid vacation per year; the terms and
     conditions of your vacation benefits shall be in accordance with the
     Company's vacation policy in effect at that time.  During your employment,
     you shall be permitted, to the extent eligible, to participate in any group
     medical, dental, life insurance and disability insurance plans, or similar
     benefit plan of the Company that is available to employees generally.
     Participation in any such plan shall be consistent with your rate of
     compensation to the extent that compensation is a determinative factor with
     respect to coverage under any such plan.

     4.2  Reimbursed Expenses.  The Company shall reimburse you for all
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     reasonable expenses actually incurred or paid by you in the performance of
     your services on behalf
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Mr. Michael Stanek                                                      [LOGO]
March 7, 2000
Page 4 of 6


     of the Company, upon prior authorization and approval in accordance with
     the Company's expense reimbursement policy as from time to time in effect.

     4.3  Stock Options.  Pursuant to Board approval, and under the terms and
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     conditions of the Company's Stock Option Plan and Stock Option Agreement,
     including the stock vesting provisions contained therein, you will be
     granted an option to purchase 293,385 (two hundred and ninety three
     thousand, three hundred and eighty five) shares of common stock of the
     Company as follows:

          a.   75,000 options (the "Initial Options") with an exercise price of
               $12 per share to vest on the commencement of your employment with
               the Company (the "Vesting Commencement Date").

          b.   121,325 options with an exercise price of $12 per share to vest
               on the one-year anniversary of the Vesting Commencement Date; and

          c.   97,060 options (the "97,060 Options") with an exercise price of
               $12 per share; one-quarter of which, or 24,265 of these options,
               shall vest on the one-year anniversary of the Vesting
               Commencement Date and one-forty-eighth (1/48/th/) of the 97,060
               Options to vest on the last day of each month for a three-year
               period thereafter.

     The Company Stock Option Plan, including the Stock Option Agreement, will
     be sent to you separately.

     4.3  Lock-Up.  You agree that you shall not sell, distribute or otherwise
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     transfer the Initial Options or the securities underlying the Initial
     Options prior to the expiration of 180 days from the date of the Vesting
     Commencement Date.


V.   Intellectual Property Rights/Confidential Information.
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     5.1  Valuable Trade Secrets. You agree that the Company is the owner of
          ----------------------
     valuable trade secrets, client, vendor, customer and contractor lists and
     other confidential and proprietary information. As such, you agree that
     your employment is contingent upon your execution of, and delivery to, the
     Company of a Confidential Information and Invention Assignment Agreement
     ("Intellectual Property Agreement") in the standard form utilized by the
     Company.

     5.2  Additional Confidential Information. You agree to maintain the
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     confidentiality of all elements of this Agreement, agreeing to an absolute
     prohibition on any disclosure or use of such information in any fashion,
     with the exception of discussions with your supervisor or myself, and
     Messrs. Jon Edwards and Tim Favia. As you are well aware the maintenance of
     confidentiality of this kind of information is critical to our
     organization.

     5.3  Equitable Remedies.  You agree that it would be impossible or
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     inadequate to measure and calculate the Company's damages from any breach
     of the covenants set
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Mr. Michael Stanek                                                      [LOGO]
March 7, 2000
Page 5 of 6


       forth in this Section as well as Sections 1, 2, 3, and 5 of the
       Intellectual Property Agreement. Accordingly, you agree that if you
       breach any of such Sections, the Company will have available, in addition
       to any other right or remedy available, the right to obtain an injunction
       from a court of competent jurisdiction restraining such breach or
       threatened breach and to specific performance of any such provision of
       this Agreement. You further agree that no bond or other security shall be
       required in obtaining, such equitable relief and you hereby consent to
       the issuance of such injunction and to the ordering of specific
       performance.

VI.    Non-Competition/Conflicting Employment. You agree that, during the term
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       of your employment with the Company, you will not engage in any other
       employment, occupation, consulting or other business activity directly
       related to the business in which the Company and/or its customers are now
       involved or become involved during the term of your employment, nor will
       you engage in any other activities that conflict with your obligations to
       the Company.

VII.   Arbitration. Except as otherwise provided in Section 5.3 above, it is
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       agreed that any dispute or controversy arising out of or relating to any
       interpretation, construction, performance or breach of this Agreement,
       shall be exclusively settled by confidential arbitration to be held in
       San Francisco County, California, in accordance with the rules then in
       effect of the American Arbitration Association. The arbitrator may grant
       injunctions or other relief in such dispute or controversy. The decision
       of the arbitrator shall be final, conclusive and binding on the parties
       to the arbitration. Judgement may be entered on the arbitrator's decision
       in any court having jurisdiction. Each party shall pay one-half of the
       costs and expenses of such arbitration, and each of us shall separately
       pay our counsel fees and expenses.

VIII.  Existing Relationship with Garage.com.  It is Company's understanding
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       that you have entered into an employment relationship with Garage.com
       which you represent and warrant to be an at-will agreement and which you
       can terminate with or without cause at any time. By signing this
       Agreement, you agree that you will simultaneously:

          a.   terminate your employment relationship with Garage.com;

          b.   comply with all obligations and contractual commitments arising
               from your employment relationship with Garage.com, including but
               not limited to, Confidentiality, Non-Disclosure and Non-
               Solicitation agreements; and

          c.   notify Garage.com and shall not exercise any and all options,
               vested and unvested, granted to you to purchase Garage.com stock.

       Mediaplex, Inc. shall indemnify you from any legal action, excluding
       fraud and any intentional torts, brought by Garage.com in connection with
       you terminating your employment relationship with that company and
       executing this employment agreement with Mediaplex, Inc.
<PAGE>

Mr. Michael Stanek                                                      [LOGO]
March 7, 2000
Page 6 of 6


IX.  General Provisions.
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     9.1  Governing Law.  This offer letter will be governed by the laws of the
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          State of California.

     9.2  Entire Agreement.  This offer letter sets forth the entire agreement
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          and understanding between the Company and you relating to your
          employment and supersedes all prior verbal discussion and written
          agreements between us.  Any subsequent change or changes in your
          duties, salary or other compensation will not affect the validity or
          scope of this agreement.  Any change to the at-will term of this
          agreement must be executed in writing and signed by you and the
          President of the Company.

     9.3  Successors/Assigns.  This agreement will be binding upon your heirs,
          ------------------
          executors, administrators and other legal representatives and will be
          for the benefit of the Company and its respective successors and
          assigns.

     Please acknowledge and confirm your acceptance of this letter by signing
and returning the enclosed copy of this offer letter, and the Confidential
Information and Invention Assignment Agreement as soon as possible. This offer
shall expire at 5:00 p.m. on March 8, 2000 if not accepted by you and executed
and returned below prior to that time.

     If you have any questions about this offer letter, please call me directly.

                              MEDIAPLEX, INC.



                              By: /s/ Gregory R. Raifman
                                  __________________________________
                                  Gregory R. Raifman
                                  Chairman and Chief Executive Officer


ACCEPTANCE:

     I accept the terms of my employment with Mediaplex, Inc. as set forth
herein.  I understand that this offer letter does not constitute a contract of
employment for any specified period of time, and that my employment relationship
may be terminated by either party with cause and with or without notice.

Mr. Michael Stanek

/s/ Michael Stanek
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March 8, 2000
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Date