October 1, 2002

Ronald A. Woessner
Zix Corporation
2711 N. Haskell Ave., Suite 2300
Dallas, TX 75204-2960

Re:  Amendment to Convertible Promissory Note

Dear Ron:

     Reference is hereby made to that certain Convertible Promissory Note, dated
July 11, 2001, made by Maptuit Corporation (the "Company") payable to ZixIt
Corporation (now Zix Corporation), a Texas corporation ("Zix"), in the principal
amount of US $2,000,000 (the "Note"). In connection with the Company's current
proposed sale and issuance of Series A-1 Convertible Preferred Shares (the
"Current Financing"), and as a condition to such Current Financing, Zix, the
Company, and Jeffrey P. Papows agree to the following (all amounts are in US
dollars):

     1.   Reduced Principal. - Zix shall not convert the Note as part of the
          Current Financing and the Note and the interest owing under the Note
          shall, subject to the terms of paragraph 2, be reduced to $900,000
          (the "Reduced Principal Amount"); provided, however, if the Company
          consummates an equity financing of $900,000 or more (other than
          pursuant to the Current Financing) from investors who do not
          participate in the Current Financing on or before January 1, 2003 (the
          "Subsequent Financing"), then as full payment for the principal and
          all accrued interest owing under the Note, the Company shall pay to
          Zix, and Zix agrees to accept, the Reduced Principal Amount. If an
          amount less than $900,000 is raised in a Subsequent Financing, then
          the parties will discuss what portion of that amount, if any, will be
          paid to Zix with respect to the Note. Furthermore, if the Company
          otherwise pays the Reduced Principal Amount prior to January 1, 2003,
          then Zix agrees to accept the Reduced Principal Amount as full payment
          for the principal and all accrued interest owing under the Note.
          Furthermore, if the Reduced Principal Amount has not already been
          fully paid (either pursuant to this paragraph 1 or otherwise), at such
          time as the Company has achieved positive cash flow for any fiscal
          quarter, the Company will pay Zix the lesser of $200,000 or 20% of the
          Reduced Principal Amount then owing within 15 business days of the end
          of such quarter to a total payment of $900,000.

          As additional consideration for Zix's agreements herein, within 10
          days from the closing of the Current Financing, (a) Mr. Papows will
          convey to Zix 1,000,000 (or equivalent) of his shares of common stock
          in the Company, subject to the proviso that if the Reduced Principal
          Amount is not paid on or by January 1, 2003, then Mr. Papows will
          convey an additional 1,000,000 (or equivalent) of such common stock
          shares to Zix and (b) the Company will pay or cause Zix to be paid
          $100,000 at the closing of the Current Financing.

<PAGE>

          The Company agrees that approximately $500,000 of loans to the Company
          from Company insiders will be converted into equity of the Company.
          The Company and Mr. Papows agree that the $200,000 ("Papows Insider
          Loan") of loans made to the Company by Mr. Papows will remain as a
          convertible note, but will not be repaid to Mr. Papows until the
          Reduced Principal Amount has been paid.

     2.   Full Note/Interest Payments. If the Note has not already been fully
          paid (either pursuant to paragraph 1 or otherwise) prior to (a) a
          Change in Control (as defined below), or (b) a Liquidation (as defined
          below), or (c) such time as the Company prepares to make or makes any
          payments on the "Papows Insider Loan", or (d) the current stated
          "Maturity Date" under the Note, then at Zix's election, (i) such of
          the Note (at the original $2,000,000 principal amount) excluding any
          and all interest minus any monies paid to Zix under this Agreement
          shall be paid by the Company to Zix in cash or (ii) such of the Note
          (at the original $2,000,000 principal amount) excluding any and all
          interest minus any monies paid to Zix under this Agreement shall
          convert into such number of common shares of the Company that is
          derived by dividing this amount by the current financing price of
          $0.071 per common share.

          A "Change of Control" shall mean the occurrence of (i) a merger,
          amalgamation, plan of arrangement, consolidation, or other transaction
          involving the Company whereby the holders of share capital of the
          Company immediately prior to such merger, amalgamation, plan of
          arrangement, consolidation, or other transaction hold, immediately
          following such merger, amalgamation, plan of arrangement,
          consolidation, or other transaction less than 50% by voting power
          (assuming for such purposes that the then-convertible Company
          non-voting securities have been converted into Company voting
          securities), of the share capital of the surviving corporation; or
          (ii) a purchase, tender, or exchange offer made to and accepted by the
          holders of more than 50% by voting power (assuming for such purposes
          that the then-convertible Company non-voting securities have been
          converted into Company voting securities), of the share capital of the
          Company; or (iii) the sale, in a single transaction or series of
          related transactions, by the Company of all or substantially all the
          assets of the Company. A "Liquidation" shall mean the occurrence of
          any liquidation, dissolution or winding up of the Company, either
          voluntary or involuntary (other than a liquidation, dissolution or
          winding up effected for the purpose of reincorporating the Company in
          another jurisdiction wherein the rights of Zix under the Note are not
          adversely affected).

     3.   Subordination - Subject to Zix's rights hereunder, Zix agrees that the
          Note and Reduced Principal Amount shall be subordinate in all respects
          to the Company's loan with MM Ventures and Pacific Business Funding
          (collectively, the "Lenders"), and shall execute any and all documents
          reasonably required by the Lenders and/or the Company.

     4.   Amendment - All other terms of the Note, including the current stated
          "Maturity Date," not expressly amended hereby shall remain in full
          force and effect.

     5.   Applicable Law - This letter agreement shall be interpreted and
          construed by the laws of the Province of Ontario (without giving
          effect to its conflict of laws rules) and the laws of Canada.

<PAGE>

     If you have any questions about the matters covered in this letter, please
call me.

                                            Very truly yours,


                                            MAPTUIT CORPORATION

                                                /s/ William K. Tapscott
                                            ------------------------------------
                                            Name:  William K. Tapscott
                                            Title: Secretary

                                                /s/ Jeffrey P. Papows
                                            ------------------------------------
                                            Jeffrey P. Papows

I have carefully read, fully understand and hereby agree to the terms and
conditions set forth above.

ZIX CORPORATION

  /s/  Ronald A. Woessner                            Date    10/2/02
-----------------------------                        ------------------
Name:  Ronald A. Woessner
Title:  S.V.P.

Source: OneCLE Business Contracts.