EXHIBIT 99.1


                  CERTIFICATION OF THE CHIEF EXECUTIVE OFFICER
                       PURSUANT TO 18 U.S.C. SECTION 1350
      AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002



         In connection with the Quarterly Report of Zix Corporation (the
"Company") on Form 10-Q for the period ending March 31, 2003 as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), I, John A.
Ryan, Chairman, President, and Chief Executive Officer of the Company, certify
to the best of my knowledge and in my capacity as an officer of the Company,
pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that:

         1.       The Report fully complies with the requirements of Section
                  13(a) or 15(d) of the Securities Exchange Act of 1934, as
                  amended; and

         2.       The information contained in the Report fairly presents, in
                  all material respects, the financial condition and results of
                  operations of the Company as of the dates and for the periods
                  expressed in the Report.

         IN WITNESS WHEREOF, the undersigned has executed this Certificate,
effective as of May 9, 2003.



                                             /s/ John A. Ryan
                                             -----------------------------------
                                             Name:  John A. Ryan
                                             Title: Chairman, President and
                                                    Chief Executive Officer


         Note: This certification accompanies the Report pursuant to Section 906
of the Sarbanes-Oxley Act of 2002 and shall not, except to the extent required
by the Sarbanes-Oxley Act of 2002, be deemed filed by the Company for purposes
of Section 18 of the Securities Exchange Act of 1934, as amended.