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 Annual Report of Zix Corporation (the "Company")
on Form 10-K for the year ending December 31, 2002 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 March 20, 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.