AMENDED AND RESTATED SEVERANCE AGREEMENT

Exhibit 10.28

Execution Version

AMENDED AND RESTATED SEVERANCE AGREEMENT

     THIS AMENDED AND RESTATED SEVERANCE AGREEMENT (this “Agreement”), dated December 18, 2008 is entered into between Zix Corporation, a Texas corporation, with its principal executive offices in Dallas, Texas (the “Company”), and Ronald A. Woessner, an individual currently residing in Plano, Texas, who is currently employed as Senior Vice President and General Counsel of the Company (“Employee”) and hereby amends and restates that certain severance agreement, dated February 25, 2002 between the parties.

Recitals

     A. The Company and Employee have entered into a Severance Agreement, dated November 4, 1996, and subsequent successors thereto (the “Severance Agreements”).

     B. The Company and Employee desire to enter into this Severance Agreement, which will replace the Severance Agreements.

     C. In consideration of the Company’s agreements herein, Employee is willing to continue working for the Company or an Affiliate, as applicable, on an “at-will” basis.

Terms and Conditions

     In consideration of the recitals and the agreements herein and other good and valuable consideration, the parties agree as follows:

1. Definitions .

     1.1 An “Acquiring Person” shall mean any person (including any “person” as such term is used in Sections 13(d)(3) or 14(d)(2) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”)) that, together with all Affiliates and Associates of such person, is the beneficial owner of 10% or more of the outstanding Common Stock. The term “Acquiring Person” shall not include the Company, any subsidiary of the Company, any employee benefit plan of the Company or subsidiary of the Company, or any person to the extent such person is holding Common Stock for or pursuant to the terms of any such plan. For the purposes of this Agreement, a person who becomes an Acquiring Person by acquiring beneficial ownership of 10% or more of the Common Stock at any time after November 4, 1996 shall continue to be an Acquiring Person whether or not such person continues to be the beneficial owner of 10% or more of the outstanding Common Stock.

     1.2 “Affiliate” and “Associate” shall have the respective meanings ascribed to such terms in Rule 12b-2 of the General Rules and Regulations under the Exchange Act in effect on the date of this Agreement.

     1.3 The Company and its Affiliates shall have “Cause” to terminate Employee’s employment upon (1) the intentional and continued failure by Employee to substantially perform

Employee’s employment duties such intentional actions involving willful and deliberate malfeasance or gross negligence in the performance of Employee’s duties (other than any such failure resulting from Employee’s incapacity due to physical or mental illness), after written demand for substantial performance is delivered by the Company or an Affiliate, as applicable, that specifically identifies the manner (such demand not to be unreasonable) in which the Company or the Affiliate, as applicable, believes Employee has not substantially performed Employee’s duties; or (2) the willful engaging by Employee in misconduct that is materially injurious to the Company or employing Affiliate, as applicable; or (3) the conviction of Employee of any felony or crime of moral turpitude that is injurious to the Company; or (4) Employee attains the mandatory retirement age specified in any applicable retirement plan of the Company or any successor-in-interest (but for purposes of this clause (4), any such mandatory retirement age shall not be less than age 65). For purposes of this definition no act, or failure to act, on Employee’s part shall be considered “willful” unless done, or omitted to be done, by Employee not in good faith and without reasonable belief that Employee’s action or omission was in the best interest of the Company or the applicable Affiliate(s), or both, as applicable. Notwithstanding the foregoing, Employee shall not be deemed to have been terminated for Cause without the following procedures having been adhered to: (a) reasonable written notice to Employee, setting forth the reasons for the Company’s or the Affiliate’s intention to terminate for Cause; (b) an opportunity for Employee, together with Employee’s counsel, to be heard before the Zix Corporation Board of Directors; and (c) delivery to Employee of a written Notice of Termination finding that, in the good faith opinion of the Zix Corporation Board of Directors, Employee was guilty of conduct set forth above in clause (1), (2) or (3) above, and specifying the particulars thereof in detail.

     1.4 “Change in Control” shall mean the occurrence of any of the following events:

     (i) The Company is merged, consolidated or reorganized into or with another corporation or other legal person, other than an Affiliate, and as a result of such merger, consolidation or reorganization less than 51% of the combined voting power to elect each class of directors of the then outstanding securities of the remaining corporation or legal person or its ultimate parent immediately after such transaction is owned, directly or indirectly, in the aggregate by persons who were shareholders, directly or indirectly, of the Company immediately prior to such merger, consolidation, or reorganization;

     (ii) The Company sells all or substantially all of its assets to any other corporation or other legal person, other than an Affiliate, and as a result of such sale less than 51% of the combined voting power to elect each class of directors of the then outstanding securities of such corporation or legal person or its ultimate parent immediately after such transaction is owned, directly or indirectly, in the aggregate by persons who were shareholders, directly or indirectly, of the Company immediately prior to such sale;

     (iii) Any Acquiring Person has become the beneficial owner (as the term “beneficial owner” is defined under Rule 13d-3 or any successor rule or regulation promulgated under the Exchange Act) of securities which when added to any securities already owned by such person would represent in the aggregate 35% or more of the then outstanding securities of the Company which are entitled to vote to elect any class of directors;

     (iv) If at any time, the Continuing Directors then serving on the Board of Directors of the Company cease for any reason to constitute at least a majority thereof;

     (v) Any occurrence that would be required to be reported in response to Item 6(e) of Schedule 14A of Regulation 14A or any successor rule or regulation promulgated under the Exchange Act; or

     (vi) Such other events that cause a change in control of the Company, as determined by the Zix Corporation Board of Directors in its sole discretion.

     1.5 “Change in Control Payment” shall mean two times the higher of (i) Employee’s annual base salary in effect on the date of the Change in Control or (ii) Employee’s highest annual base salary during the term of Employee’s employment with the Company.

     1.6 A “Continuing Director” shall mean a director of the Company who (i) is not an Acquiring Person or an Affiliate or Associate thereof, or a representative of an Acquiring Person or nominated for election by an Acquiring Person, and (ii) was either a member of the Board of Directors of the Company on the date of this Agreement or subsequently became a director of the Company and whose initial election or initial nomination for election by the Company’s shareholders was approved by a majority of the Continuing Directors then on the Board of Directors of the Company.

     1.7 “Disability” shall mean that the Employee is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment that can be expected to result in death or can be expected to last for a continuous period of not less than 12 months.

     1.8 “Good Reason” shall mean the occurrence of any of the following events:

     (a) any material diminution in Employee’s duties that has not been cured within thirty days after notice of such noncompliance has been given (within 30 days of the alleged material diminution) by Employee to the Company or the employing Affiliate, as applicable. A change in title or duties will not be considered to be a “material diminution” in duties if, after such change, Employee is an officer of the Company; Employee’s reporting relationship does not change or Employee reports to the Company’s Chief Executive Officer or Chief Operating Officer; and a substantial portion of Employee’s duties are in Employee’s field of professional training or experience.

     (b) a reduction of more than 10% in Employee’s base salary (with the 10% being cumulative over the term of Employee’s employment), but any percentage reduction that is actually made is made against the Employee’s then current base salary).

EXAMPLE: assume Employee’s base salary is $100,000. The Company or Affiliate, as applicable, is permitted to reduce Employee’s base salary by up to 10% ($10,000) without giving Employee “Good Reason” to terminate employment. Any further salary reductions

would constitute “Good Reason” to terminate employment.

     (c) any purported termination for Cause of Employee’s employment that is not effected pursuant to the procedural requirements of Subsection 1.3.

     (d) the location of Employee’s place of employment is moved more than 50 miles from its current location.

     1.9 “Notice of Termination” shall mean a notice that indicates the specific reasons for termination and shall set forth in reasonable detail the facts and circumstances claimed to provide a basis for termination of Employee’s employment.

     1.10 “Person” shall mean an individual, a corporation, a partnership, an association, a joint-stock company, a trust, an incorporated organization or a government or political subdivision thereof.

     1.11 “Severance Payment” shall mean an amount equal to 150% of Employee’s highest annual base salary during the term of Employee’s employment with the Company; provided that , if the event giving rise to the Severance Payment occurs on or before the 180th day following a Change in Control (with the day immediately following the day of the occurrence of the Change in Control being day “1”), then the amount of the Severance Payment shall be the greater of (i) the amount provided for in this sentence or (ii) the amount provided for in Section 3 (as if Employee had resigned from employment pursuant to Section 3).

2.  Severance Payment . From and after the date hereof, upon the occurrence of any of the following events the Company will pay to Employee the Severance Payment (in accordance with Section 4) and Employee’s options to acquire the Company’s stock shall become vested in full (regardless of whether the options were granted before or are granted after the date of this Agreement):

     To terminate Employee’s employment other than for Cause pursuant to 2(a), the Company or the employing Affiliate, as applicable, shall give Emp