AMENDMENT TO AMENDED AND RESTATED CONVERTIBLE NOTE

Exhibit 4.1

AMENDMENT NO. 2

dated as of December 9, 2005

by and between

ZIX CORPORATION

and

OMICRON MASTER TRUST

Relating to

AMENDED AND RESTATED

CONVERTIBLE NOTE DUE 2005-2008

and

AMENDED AND RESTATED

COMMON STOCK PURCHASE WARRANT

ZIX CORPORATION

AMENDMENT NO. 2

Relating to

AMENDED AND RESTATED

CONVERTIBLE NOTE DUE 2005-2008

and

AMENDED AND RESTATED

COMMON STOCK PURCHASE WARRANT

TABLE OF CONTENTS

AMENDMENT NO. 2

           THIS AMENDMENT NO. 2, dated as of December 9, 2005 (this “Agreement”), by and between ZIX CORPORATION, a Texas corporation (the “Company”), and OMICRON MASTER TRUST , a Bermuda trust (the “Purchaser”), amends the AMENDED AND RESTATED CONVERTIBLE NOTE DUE 2005-2008 in the original principal amount of $10,000,000 issued by the Company (the “Note”), the AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT, and the PURCHASE AGREEMENT (such capitalized term and all other capitalized terms used herein having the respective meanings provided herein).

W I T N E S S E T H :

           WHEREAS, the Company and the Purchaser have previously executed and delivered, one to the other, the Purchase Agreement and the Registration Rights Agreement, and the Company has issued the Note to the Purchaser;

           WHEREAS, the Company and the Purchaser wish to amend certain terms of the Note and to confirm the meaning of certain provisions of the Registration Rights Agreement, upon the terms and subject to the conditions of this Agreement;

           NOW THEREFORE, in consideration of the premises and the mutual covenants made herein and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

           1. Definitions.

           1.1 As used in this Agreement, the terms “Agreement”, “Company”, “Note”, “Registration Rights Agreement” and “Purchaser” shall have the respective meanings assigned to such terms in the introductory paragraph of this Agreement.

           1.2 Capitalized terms used in this Agreement and not defined in this Agreement shall have the respective meanings provided in the Note or if not defined in the Note, as defined in the Registration Rights Agreement and if not defined in the Note or the Registration Rights Agreement, as defined in the Purchase Agreement.

           1.3 All the agreements or instruments herein defined shall mean such agreements or instruments as the same may from time to time be supplemented or amended or the terms thereof waived or modified to the extent permitted by, and in accordance with, the terms thereof and of this Agreement.

           1.4 The following terms shall have the following meanings (such meanings to be equally applicable to both the singular and plural forms of the terms defined):

          “Amendment No. 1” means Amendment No. 1 to Purchase Agreement, dated as of April 13, 2005, by and between the Company and the Purchaser.

          “Effective Time” means the date on which and time at which the Company and the Purchaser execute and deliver this Agreement, one to the other.

          “First Registration Statement” means the Company’s Registration Statement on Form S-3, Registration No. 333-120548, ordered effective by the SEC on February 3, 2005.

          “Other Agreement” means the Amendment No. 2, dated as of the date hereof, between the Company and the holder of the Other Note relating to, among other things, amendment of the Other Note.

          “Purchase Agreement” means the Purchase Agreement, dated as of November 1, 2004, by and between the Company and the Purchaser, as amended by Amendment No. 1.

          “Second Registration Statement” means the Company’s Registration Statement on Form S-3, Registration No. 333-124318, ordered effective by the SEC on July 20, 2005.

           2. Amendments and Confirmation. The following amendments in Section 2.1 shall become effective at the Effective Time.

           2.1 Partial Redemption of the Note. (a) As contemplated by Section 2(d)(2) of the Note, on or before December 9, 2005 the Company shall redeem the remaining $1,950,687.00 outstanding principal amount of the principal installment of the Note scheduled to be due on November 2, 2008. The Optional Redemption Notice for such redemption is as follows:

ZIX CORPORATION

OPTIONAL REDEMPTION NOTICE
(Section 2(b) of Amended and Restated
Convertible Note due 2005-2008)

TO: Omicron Master Trust

     1. Pursuant to the terms of the Amended and Restated Convertible Note due 2005-2008 (the “Note”), Zix Corporation, a Texas corporation (the “Company”), hereby notifies the above-named Holder that the Company is exercising its right to redeem the Note in accordance with Section 2(b) of the Note as set forth below:

          (i) The cash portion of Optional Redemption Consideration (based on the principal amount of the Note outstanding on the date this Notice is given) is $2,063,594.80.

          (ii) The Redemption Warrant issuable upon such redemption (based on the principal amount of the Note outstanding on the date this Notice is given) initially will entitle the holder to purchase 145,032 shares of Common Stock at a price of $5.38 per share.

          (iii) The Optional Redemption Date is December 9, 2005.

     2. All of the conditions of Section 2(b) of the Note for this redemption have been satisfied.

     3. Capitalized terms used herein and not otherwise defined herein have the respective meanings provided in the Note.

*Deemed executed by the signature of the Company that appears at the end of this Agreement.

Notwithstanding the period specified in the Note for the giving of an Optional Redemption Notice, the Purchaser agrees to accept the foregoing Optional Redemption Notice. Solely for purposes of permitting the Company to give the foregoing Optional Redemption Notice, and not for purposes of otherwise relieving the Company of its obligation to comply, or the Purchaser’s rights under, the following provisions of the Note, the Purchaser hereby also waives the following additional requirements related to such redemption:

          (1) Section 2(c)(1)(C) of the Note regarding the availability of the Registration Statement for use by the Purchaser;

          (2) Section 2(c)(1)(G) regarding the absence of a Maximum Share Amount Deficiency; and

          (3) Section (3)(o)(2) of the Note as to reporting the Share Redemption completed on December 1, 2005 so long as the Company reports the information specified in such Section 3(o)(2) in the Current Report on Form 8-K filed by the Company as required by Section 6.3.

          (b) The cash portion of the Optional Redemption Consideration for such redemption shall be paid by release of cash Collateral from the lien and security interest of the Security Agreement pursuant to Section 15(e) thereof. The Purchaser hereby consents to such release of Collateral pursuant to Section 15(e) of the Security Agreement.

           2.2 Concerning the Warrant. For purposes of Section 8(f) of the Warrant, the redemption of the Note provided for in Section 2.1 of this Agreement shall be treated as a Share Redemption but in lieu of the number of shares of Common Stock determined under Section 8(f) of the Warrant that would be repriced by reason thereof, the Purchase Price under and as defined in the Warrant shall be reduced to $1.44 for 119,273 shares of Common Stock issuable upon exercise of the Warrant.

           2.3 Concerning the Purchase Agreement and the Security Agreement. On November 23, 2005 the Company gave the Purchaser a Maximum Share Amount Notice. Notwithstanding the provisions of Section 6.16 of the Purchase Agreement and the provisions of the Security Agreement, the Company and the Purchaser agree as follows:

          (a) The Company shall seek, and use its best efforts to obtain, the Stockholder Approval by May 1, 2006, rather than by the date that is 60 days after the Maximum Share Amount Notice Date for such Maximum Share Amount Notice.

          (b) The Purchaser’s right to require redemption of the Note during the 30-day period otherwise provided for in Section 6.16(b)(2) of the Purchase Agreement in respect of such Maximum Share Amount Notice shall be tolled until the earlier of (1) May 1, 2006 and (2) the date on which the Stockholder Meeting is held (the “Redemption Right Date”), with the result that the Purchaser’s right to require redemption of the Note pursuant to Section 6.16(b)(3) of the Purchase Agreement shall be a right to require such redemption whether or not the Company obtains Stockholder Approval, and such right may be exercised commencing on the Redemption Right Date.

          (c) Notwithstanding Section 15(c)(6) of the Security Agreement, upon the later of (x) December 30, 2005 and (y) the date on which the Company has by Share Redemption or cash redemption reduced the aggregate outstanding principal amount of the Notes to $10,000,000 or less, the Company shall be entitled to release of all cash Collateral in excess of $7,936,405.20 upon the Company’s request therefor in accordance with Section 15(c) of the Security Agreement and satisfaction of the other requirements of Section 15(c) of the Security Agreement. Thereafter, until such time as no Maximum Share Amount Deficiency exists, if the aggregate outstanding principal amount of the Notes is reduced below $10,000,000 the Company shall be entitled, upon its request and the satisfaction of the requirements of Section 15(c) of the Security Agreement other than Section 15(c)(6) of the Security Agreement, to release of cash Collateral in excess of the lesser of (x) $7,936,405.20 and (y) the aggregate outstanding principal amount of the Notes. If no Maximum Share Amount Deficiency exists, then the provisions of Section 15(c) of the Security Agreement, without regard to the foregoing provisions of this Section 2.3(c), shall once again be in effect.

          (d) Notwithstanding Section 15(c)(6) of the Security Agreement, until the earlier of (x) the date no Maximum Share Amount Deficiency exists a