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                                                                     EXHIBIT 4.3

                          REGISTRATION RIGHTS AGREEMENT

         REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT"), dated as of March
3, 2003, by and among Zix Corporation (formerly known as Zixit Corporation), a
Texas corporation, with headquarters located at 2711 N. Haskell Avenue, Suite
2300, Dallas, Texas 75204 (the "COMPANY"), and the undersigned investors (each,
an "INVESTOR" and collectively, the "INVESTORS").

         WHEREAS:

         A. In connection with the Agreement Regarding Exercise and Issuance of
Warrants by and among the parties hereto of even date herewith (the "WARRANT
AGREEMENT"), the Company has agreed, upon the terms and subject to the
conditions of the Warrant Agreement, to issue to the Investors warrants (the
"REPLACEMENT WARRANTS," and as exercised, the "REPLACEMENT WARRANT SHARES") to
purchase shares of the Company's common stock, $0.01 par value per share (the
"COMMON STOCK");

         B. To induce the Investors to execute and deliver the Warrant
Agreement, the Company has agreed to provide certain registration rights under
the Securities Act of 1933, as amended, and the rules and regulations
thereunder, or any similar successor statute (collectively, the "1933 ACT"), and
applicable state securities laws.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the Company and each
of the Investors hereby agree as follows:

         1. DEFINITIONS.

                  As used in this Agreement, the following terms shall have the
following meanings:

                  a. "HOLDER" means an Investor, any transferee or assignee
thereof to whom an Investor assigns its rights under this Agreement and who
agrees to become bound by the provisions of this Agreement in accordance with
Section 9 and any transferee or assignee thereof to whom a transferee or
assignee assigns its rights under this Agreement and who agrees to become bound
by the provisions of this Agreement in accordance with Section 9.

                  b. "PERSON" means an individual, a limited liability company,
a partnership, a joint venture, a corporation, a trust, an unincorporated
organization and a governmental or any department or agency thereof.

                  c. "REGISTER," "REGISTERED," and "REGISTRATION" refer to a
registration effected by preparing and filing one or more Registration
Statements (as defined below) in compliance with the 1933 Act and pursuant to
Rule 415 under the 1933 Act or any successor rule providing for offering
securities on a continuous or delayed basis ("RULE 415"), and the declaration or
ordering of effectiveness of such Registration Statement(s) by the United States
Securities and Exchange Commission (the "SEC").

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                  d. "REGISTRABLE SECURITIES" means (i) the Replacement Warrant
Shares issued or issuable upon exercise of the Replacement Warrants and (ii) any
shares of capital stock issued or issuable with respect to the Replacement
Warrant Shares and the Replacement Warrants as a result of any stock split,
stock dividend, recapitalization, exchange or similar event or otherwise,
without regard to any limitations on exercises of Replacement Warrants.

                  e. "REGISTRATION STATEMENT" means a registration statement or
registration statements of the Company filed under the 1933 Act covering the
Registrable Securities.

Capitalized terms used herein and not otherwise defined herein shall have the
respective meanings set forth in the Warrant Agreement.

         2. REGISTRATION.

                  a. Mandatory Registration. The Company shall prepare, and, as
soon as practicable but in no event later than 15 days after the Final Closing
Date (as defined in the Warrant Agreement) (the "FILING DEADLINE"), file with
the SEC a Registration Statement on Form S-3 covering the resale of all of the
Registrable Securities. In the event that Form S-3 is unavailable for such a
registration, the Company shall use such other form as is available for such a
registration, subject to the provisions of Section 2(d). The Registration
Statement prepared pursuant hereto shall register for resale at least that
number of shares of Common Stock equal to 110% of the number of Replacement
Warrant Shares issuable upon exercise of all the outstanding Replacement
Warrants (without regard to any limitations on the exercise thereof) as of the
second trading day immediately preceding the date the Registration Statement is
initially filed with the SEC, subject to adjustment as provided in Section 2(e).
The Company shall use its best efforts to have the Registration Statement
declared effective by the SEC as soon as practicable, but in no event later than
the date which is 90 days after the Final Closing Date (the "EFFECTIVENESS
DEADLINE").

                  b. Allocation of Registrable Securities. The initial number of
Registrable Securities included in any Registration Statement and each increase
in the number of Registrable Securities included therein shall be allocated pro
rata among the Holders based on the number of Registrable Securities held by
each Holder at the time the Registration Statement covering such initial number
of Registrable Securities or increase thereof is declared effective by the SEC.
In the event that a Holder sells or otherwise transfers any of such Holder's
Registrable Securities, each transferee shall be allocated a pro rata portion of
the then remaining number of Registrable Securities included in such
Registration Statement for such transferor. Any shares of Common Stock included
in a Registration Statement and which remain allocated to any Person which
ceases to hold any Registrable Securities covered by such Registration Statement
shall be allocated to the remaining Holders, pro rata based on the number of
Registrable Securities then held by such Holders which are covered by such
Registration Statement.

                  c. Legal Counsel. Subject to Section 5 hereof, the Investors
holding securities representing at least two-thirds (2/3) of the Registrable
Securities shall have the right to select one legal counsel to review and
oversee any offering pursuant to this Section 2 ("LEGAL COUNSEL"), which shall
be Katten Muchin Zavis Rosenman or such other counsel as thereafter designated
by the holders of at least two-thirds (2/3) of the Registrable Securities. The
Company shall reasonably cooperate with Legal Counsel in performing the
Company's obligations under this Agreement.



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                  d. Ineligibility for Form S-3. In the event that Form S-3 is
not available for the registration of the resale of Registrable Securities
hereunder, the Company shall (i) register the resale of the Registrable
Securities on another appropriate form reasonably acceptable to the holder of at
least two-thirds (2/3) of the Registrable Securities and (ii) undertake to
register the Registrable Securities on Form S-3 as soon as such form is
available, provided that the Company shall maintain the effectiveness of the
Registration Statement then in effect until such time as a Registration
Statement on Form S-3 covering the Registrable Securities has been declared
effective by the SEC.

                  e. Sufficient Number of Shares Registered. In the event the
number of shares available under a Registration Statement filed pursuant to
Section 2(a) is insufficient to cover all of the Registrable Securities required
to be covered by such Registration Statement or a Holder's allocated portion of
the Registrable Securities pursuant to Section 2(b), the Company shall amend the
Registration Statement, or file a new Registration Statement (on the short form
available therefor, if applicable), or both, so as to cover at least 100% of the
number of such Registrable Securities as of the trading day immediately
preceding the date of the filing of such amendment or new Registration
Statement, in each case, as soon as practicable, but in any event not later than
fifteen (15) days after the necessity therefor arises. The Company shall use its
best efforts to cause such amendment and/or new Registration Statement to become
effective as soon as practicable following the filing thereof. For purposes of
the foregoing provision, the number of shares available under a Registration
Statement shall be deemed "insufficient to cover all of the Registrable
Securities" if at any time the number of Registrable Securities issued or
issuable upon exercise of the Replacement Warrants covered by such Registration
Statement is greater than the number of shares of Common Stock available for
resale under such Registration Statement. The calculation set forth in the
foregoing sentence shall be made without regard to any limitations on the
exercise of the Replacement Warrants and such calculation shall assume that the
Replacement Warrants are then exercisable into shares of Common Stock at the
then prevailing Warrant Exercise Price (as defined in the Replacement Warrants).

                  f. Effect of Failure to File and Obtain and Maintain
Effectiveness of Registration Statement. If (i) a Registration Statement
covering all the Registrable Securities and required to be filed by the Company
pursuant to this Agreement is not (A) filed with the SEC on or before the Fling
Deadline or (B) declared effective by the SEC on or before the Effectiveness
Deadline or (ii) on any day after the Registration Statement has been declared
effective by the SEC sales of all the Registrable Securities required to be
included on such Registration Statement cannot be made (other than during an
Allowable Grace Period (as defined in Section 3(t))) pursuant to the
Registration Statement (including, without limitation, because of a failure to
keep the Registration Statement effective, to disclose such information as is
necessary for sales to be made pursuant to the Registration Statement or to
register sufficient shares of Common Stock), then, as partial relief for the
damages to any holder by reason of any such delay in or reduction of its ability
to sell the underlying shares of Common Stock (which remedy shall not be
exclusive of any other remedies available at law or in equity), the Company
shall pay to each holder of Replacement Warrants an amount in cash equal to the
product of (i) the aggregate number of Registrable Securities held by such
holder, multiplied by (ii) $5.00 (subject to adjustment for stock splits, stock
dividends, stock combinations and other similar transaction after the date of
this Agreement), multiplied by (iii) the sum of (A) 0.02, if the Registration
Statement is not filed by the Filing Deadline, plus (B) 0.02, if the
Registration Statement is not declared effective by the Effectiveness Deadline,
plus, (C) the product of (I) 0.000667 multiplied by (II) the sum (without
duplication) of (x) the number of days after the Filing Deadline that such
Registration Statement is not filed with the SEC, plus (y) the number of days
after the




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applicable Effectiveness Deadline that the Registration Statement is not
declared effective by the SEC, plus (z) the number of days after the
Registration Statement has been declared effective by the SEC that such
Registration Statement is not available (other than during an Allowable Grace
Period) for the sale of at least all the Registrable Securities required to be
included on such Registration Statement pursuant to Section 2(e). The payments
to which a holder shall be entitled pursuant to this Section 2(f) are referred
to herein as "REGISTRATION DELAY PAYMENTS." Registration Delay Payments shall be
paid on the earlier of (I) the last day of the calendar month during which such
Registration Delay Payments are incurred and (II) the third Business Day after
the event or failure giving rise to the Registration Delay Payments is cured. In
the event the Company fails to make Registration Delay Payments in a timely
manner, such Registration Delay Payments shall bear interest at the rate of the
lesser of 2.0% per month (prorated for partial months) or the highest lawful
maximum interest rate, in each case, until paid in full.

         3. RELATED OBLIGATIONS.

                  At such time as the Company is obligated to file a
Registration Statement with the SEC pursuant to Section 2(a) or 2(e), the
Company will use its best efforts to effect the registration of the Registrable
Securities in accordance with the intended method of disposition thereof and,
pursuant thereto, the Company shall have the following obligations:

                  a. The Company shall promptly prepare and file with the SEC a
Registration Statement with respect to the applicable Registrable Securities
(but in no event later than the applicable Filing Deadline) and use its best
efforts to cause such Registration Statement relating to the Registrable
Securities to become effective as soon as practicable after such filing (but in
no event later than the applicable Effectiveness Deadline). The Company shall
keep each Registration Statement effective pursuant to Rule 415 at all times
until the earlier of (i) the date as of which the Holders may sell all of the
Registrable Securities covered by such Registration Statement without
restriction pursuant to Rule 144(k) (or successor thereto) promulgated under the
1933 Act or (ii) the date on which the Holders shall have sold all the
Registrable Securities covered by such Registration Statement (the "REGISTRATION
PERIOD"). Such Registration Statement (including any amendments or supplements
thereto and prospectuses contained therein) shall not contain any untrue
statement of a material fact or omit to state a material fact required to be
stated therein, or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading. The term "best efforts"
shall mean, among other things, that the Company shall submit to the SEC, within
two (2) Business Days after the Company learns that no review of a particular
Registration Statement will be made by the staff of the SEC or that the staff
has no further comments on the Registration Statement, as the case may be, a
request for acceleration of effectiveness of such Registration Statement to a
time and date not later than 48 hours after the submission of such request.

                  b. The Company shall prepare and file with the SEC such
amendments (including post-effective amendments) and supplements to a
Registration Statement and the prospectus used in connection with such
Registration Statement, which prospectus is to be filed pursuant to Rule 424
promulgated under the 1933 Act, as may be necessary to keep such Registration
Statement effective at all times during the Registration Period, and, during
such period, comply with the provisions of the 1933 Act with respect to the
disposition of all Registrable Securities of the Company covered by such
Registration Statement until such time as all of such Registrable Securities
shall have been disposed of in accordance with the intended methods of
disposition by the seller or sellers thereof as set forth in such Registration
Statement. In the case of amendments and supplements to a Registration Statement
which are required to be




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filed pursuant to this Agreement (including pursuant to this Section 3(b)) by
reason of the Company filing a report on Form 10-K, Form 10-Q or Form 8-K or any
analogous report under the Securities Exchange Act of 1934, as amended (the
"1934 ACT"), the Company shall have incorporated such report by reference into
the Registration Statement, if applicable, or shall file such amendments or
supplements with the SEC on the same day on which the 1934 Act report is filed
which created the requirement for the Company to amend or supplement the
Registration Statement.

                  c. The Company shall (A) permit Legal Counsel to review and
comment upon (i) the initial Registration Statement at least four (4) Business
Days prior to its filing with the SEC and (ii) all other Registration Statements
and all amendments and supplements to all Registration Statements (except for
Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports
on Form 8-K and any similar or successor reports) within a reasonable number of
days prior to their filing with the SEC, and (B) not file any document,
registration statement, amendment or supplement described in the foregoing
clause (A) in a form to which Legal Counsel reasonably objects. The Company
shall not submit a request for acceleration of the effectiveness of a
Registration Statement or any amendment or supplement thereto without providing
prior notice thereof to Legal Counsel and each Holder. The Company shall furnish
to Legal Counsel, without charge, (i) promptly after the same is prepared and
filed with the SEC, one copy of any Registration Statement and any amendment(s)
thereto, including financial statements and schedules, all documents
incorporated therein by reference, and all exhibits and (ii) upon the
effectiveness of any Registration Statement, one copy of the prospectus included
in such Registration Statement and all amendments and supplements thereto. The
Company shall reasonably cooperate with Legal Counsel in performing the
Company's obligations pursuant to this Section 3.

                  d. The Company shall furnish to each Holder whose Registrable
Securities are included in any Registration Statement, without charge, (i)
promptly after the same is prepared and filed with the SEC, at least one copy of
such Registration Statement and any amendment(s) thereto, including financial
statements and schedules, all documents incorporated therein by reference, all
exhibits and each preliminary prospectus, (ii) upon the effectiveness of any
Registration Statement, ten (10) copies of the prospectus included in such
Registration Statement and all amendments and supplements thereto (or such other
number of copies as such Holder may reasonably request) and (iii) such other
documents, including copies of any preliminary or final prospectus, as such
Holder may reasonably request from time to time in order to facilitate the
disposition of the Registrable Securities owned by such Holder.

                  e. The Company shall use its best efforts to (i) register and
qualify, unless an exemption from registration and qualification applies, the
resale by the Holders of the Registrable Securities covered by a Registration
Statement under such other securities or "blue sky" laws of all the states of
the United States, (ii) prepare and file in those jurisdictions, such amendments
(including post-effective amendments) and supplements to such registrations and
qualifications as may be necessary to maintain the effectiveness thereof during
the Registration Period, (iii) take such other actions as may be necessary to
maintain such registrations and qualifications in effect at all times during the
Registration Period, and (iv) take all other actions reasonably necessary or
advisable to qualify the Registrable Securities for sale in such jurisdictions;
provided, however, that the Company shall not be required in connection
therewith or as a condition thereto to (x) qualify to do business in any
jurisdiction where it would not otherwise be required to qualify but for this
Section 3(e), (y) subject itself to general taxation in any such jurisdiction,
or (z) file a general consent to service of process in any such jurisdiction.




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The Company shall promptly notify Legal Counsel and each Holder who holds
Registrable Securities of the receipt by the Company of any notification with
respect to the suspension of the registration or qualification of any of the
Registrable Securities for sale under the securities or "blue sky" laws of any
jurisdiction in the United States or its receipt of actual notice of the
initiation or threatening of any proceeding for such purpose.

                  f. The Company shall notify Legal Counsel and each Holder in
writing of the happening of any event, as promptly as practicable after becoming
aware of such event, as a result of which the prospectus included in a
Registration Statement, as then in effect, includes an untrue statement of a
material fact or omission to state a material fact required to be stated therein
or necessary to make the statements therein, in light of the circumstances under
which they were made, not misleading (provided that in no event shall such
notice contain any material, nonpublic information), and promptly prepare a
supplement or amendment to such Registration Statement to correct such untrue
statement or omission, and deliver ten (10) copies of such supplement or
amendment to Legal Counsel and each Holder (or such other number of copies as
Legal Counsel or such Holder may reasonably request). The Company shall also
promptly notify Legal Counsel and each Holder in writing (i) when a prospectus
or any prospectus supplement or post-effective amendment has been filed, and
when a Registration Statement or any post-effective amendment has become
effective (notification of such effectiveness shall be delivered to Legal
Counsel and each Holder by facsimile on the same day of such effectiveness and
by overnight mail), (ii) of any request by the SEC for amendments or supplements
to a Registration Statement or related prospectus or related information, and
(iii) of the Company's reasonable determination that a post-effective amendment
to a Registration Statement would be appropriate.

                  g. The Company shall use its best efforts to prevent the
issuance of any stop order or other suspension of effectiveness of a
Registration Statement, or the suspension of the qualification of any of the
Registrable Securities for sale in any jurisdiction and, if such an order or
suspension is issued, to obtain the withdrawal of such order or suspension at
the earliest possible moment and to notify Legal Counsel and each Holder who
holds Registrable Securities being sold of the issuance of such order and the
resolution thereof or its receipt of actual notice of the initiation or threat
of any proceeding for such purpose.

                  h. At the reasonable request (in the context of the securities
laws) of any Holder, the Company shall furnish to such Holder, on the date of
the effectiveness of the Registration Statement and thereafter from time to time
on such dates as a Holder may reasonably request (i) a letter, dated such date,
from the Company's independent certified public accountants in form and
substance as is customarily given by independent certified public accountants to
underwriters in an underwritten public offering, addressed to the Holders, and
(ii) an opinion, dated as of such date, of counsel representing the Company for
purposes of such Registration Statement, in form, scope and substance as is
customarily given in an underwritten public offering, addressed to the Holders.

                  i. At the reasonable request (in the context of the securities
laws) of any Holder, the Company shall make available for inspection during
regular business hours by (i) any Holder, (ii) Legal Counsel and (iii) one firm
of accountants or other agents retained by the Holders (collectively, the
"INSPECTORS"), all pertinent financial and other records, and pertinent
corporate documents and properties of the Company (collectively, the "RECORDS"),
as shall be reasonably deemed necessary by each Inspector, and cause the
Company's officers, directors and employees to supply all information which any
Inspector may reasonably request; provided,




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however, that each Inspector shall agree to hold in strict confidence and shall
not make any disclosure (except to a Holder) or use of any Record or other
information which the Company determines in good faith to be confidential, and
of which determination the Inspectors are so notified, unless (a) the disclosure
of such Records is necessary to avoid or correct a misstatement or omission in
any Registration Statement or is otherwise required under the 1933 Act, (b) the
release of such Records is ordered pursuant to a final, non-appealable subpoena
or order from a court or government body of competent jurisdiction, or (c) the
information in such Records has been made generally available to the public
other than by disclosure in violation of this or any other agreement of which
the Inspector has knowledge. Each Holder agrees that it shall, upon learning
that disclosure of such Records is sought in or by a court or governmental body
of competent jurisdiction or through other means, give prompt notice to the
Company and allow the Company, at its expense, to undertake appropriate action
to prevent disclosure of, or to obtain a protective order for, the Records
deemed confidential. Each Inspector which exercises its rights under this
Section 3(i) shall be obligated to execute a non-disclosure agreement containing
such reasonable terms as the Company may request. The fees and expenses of the
Inspectors shall be borne by the applicable Holder.

                  j. The Company shall hold in confidence and not make any
disclosure of information concerning a Holder provided to the Company unless (i)
disclosure of such information is necessary to comply with federal or state
securities laws, (ii) the disclosure of such information is necessary to avoid
or correct a misstatement or omission in any Registration Statement, (iii) the
release of such information is ordered pursuant to a subpoena or other final,
non-appealable order from a court or governmental body of competent
jurisdiction, or (iv) such information has been made generally available to the
public other than by disclosure in violation of this Agreement or any other
agreement. The Company agrees that it shall, upon learning that disclosure of
such information concerning a Holder is sought in or by a court or governmental
body of competent jurisdiction or through other means, give prompt written
notice to such Holder and allow such Holder, at the Holder's expense, to
undertake appropriate action to prevent disclosure of, or to obtain a protective
order for, such information.

                  k. The Company shall use its best efforts either to (i) cause
all the Registrable Securities covered by a Registration Statement to be listed
on each securities exchange on which securities of the same class or series
issued by the Company are then listed, if any, if the listing of such
Registrable Securities is then permitted under the rules of such exchange, or
(ii) secure designation and quotation of all the Registrable Securities covered
by the Registration Statement on the Nasdaq National Market System, or (iii) if,
despite the Company's best efforts to satisfy the preceding clause (i) or (ii),
the Company is unsuccessful in satisfying the preceding clause (i) or (ii), to
secure the inclusion for quotation on The Nasdaq SmallCap Market for such
Registrable Securities and, without limiting the generality of the foregoing, to
arrange for at least two market makers to register with the National Association
of Securities Dealers, Inc. ("NASD") as such with respect to such Registrable
Securities. The Company shall pay all fees and expenses in connection with
satisfying its obligation under this Section 3(k).

                  l. The Company shall cooperate with the Holders who hold
Registrable Securities being offered and, to the extent applicable, facilitate
the timely preparation and delivery of certificates (not bearing any restrictive
legend) representing the Registrable Securities to be offered pursuant to a
Registration Statement and enable such certificates to be in such denominations
or amounts, as the case may be, as the Holders may reasonably request and
registered in such names as the Holders may request.




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<PAGE>

                  m. The Company shall provide a transfer agent and registrar of
all such Registrable Securities not later than the effective date of the
applicable Registration Statement.

                  n. If requested by a Holder, the Company shall (i) as soon as
practicable incorporate in a prospectus supplement or post-effective amendment
such information as a Holder requests to be included therein relating to the
sale and distribution of Registrable Securities, including, without limitation,
information with respect to the number of Registrable Securities being offered
or sold, the purchase price being paid therefor and any other terms of the
offering of the Registrable Securities to be sold in such offering; (ii) as soon
as practicable make all required filings of such prospectus supplement or
post-effective amendment after being notified of the matters to be incorporated
in such prospectus supplement or post-effective amendment; and (iii) as soon as
practicable, supplement or make amendments to any Registration Statement if
reasonably requested by a Holder of such Registrable Securities.

                  o. The Company shall use its best efforts to cause the
Registrable Securities covered by the applicable Registration Statement to be
registered with or approved by such other governmental agencies or authorities
in the United States as may be necessary to consummate the disposition of such
Registrable Securities.

                  p. The Company shall make generally available to its security
holders as soon as practical, but not later than 90 days after the close of the
period covered thereby, an earnings statement (in form complying with the
provisions of Rule 158 under the 1933 Act) covering a twelve-month period
beginning not later than the first day of the Company's fiscal quarter next
following the effective date of the Registration Statement.

                  q. The Company shall otherwise use its best efforts to comply
with all applicable rules and regulations of the SEC in connection with any
registration hereunder.

                  r. Within two (2) Business Days after a Registration Statement
which covers applicable Registrable Securities is ordered effective by the SEC,
the Company shall deliver, and shall cause legal counsel for the Company to
deliver, to the transfer agent for such Registrable Securities (with copies to
the Holders whose Registrable Securities are included in such Registration
Statement) confirmation that such Registration Statement has been declared
effective by the SEC in the form attached hereto as Exhibit A.

                  s. The Company shall take all other reasonable actions
necessary to expedite and facilitate disposition by the Holders of Registrable
Securities pursuant to a Registration Statement.

                  t. Notwithstanding anything to the contrary in Section 3(f),
at any time after the applicable Registration Statement has been declared
effective by the SEC, the Company may delay the disclosure of material
non-public information concerning the Company the disclosure of which at the
time is not, in the good faith opinion of the Board of Directors of the Company
and its counsel, in the best interest of the Company and, in the opinion of
counsel to the Company, otherwise required (a "GRACE PERIOD"); provided, that
the Company shall promptly (i) notify the Holders in writing of the existence of
material non-public information giving rise to a Grace Period (provided that in
each notice the Company will not disclose the content of such material
non-public information to the Holders) and the date on which the Grace Period
will begin, and (ii) notify the Holders in writing of the date on which the
Grace Period ends; and, provided further, that no Grace Period shall exceed 15
consecutive days and during any 365 day


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<PAGE>

period such Grace Periods shall not exceed an aggregate of 30 days and the first
day of any Grace Period must be at least two (2) trading days after the last day
of any prior Grace Period (an "ALLOWABLE GRACE PERIOD"). For purposes of
determining the length of a Grace Period above, the Grace Period shall begin on
and include the date the holders receive the notice referred to in clause (i)
and shall end on and include the later of the date the holders receive the
notice referred to in clause (ii) and the date referred to in such notice. The
provisions of 3(g) hereof shall not be applicable during the period of any
Allowable Grace Period. Upon expiration of the Grace Period, the Company shall
again be bound by the first sentence of Section 3(f) with respect to the
information giving rise thereto unless such material non-public information is
no longer applicable.

         4. OBLIGATIONS OF THE HOLDERS.

                  a. At least seven (7) Business Days prior to the first
anticipated filing date of a Registration Statement and at lease five (5)
Business Days prior to the filing of any amendment or supplement to a
Registration Statement, the Company shall notify each Holder in writing of the
information, if any, the Company requires from each such Holder if such Holder
elects to have any of such Holder's Registrable Securities included in such
Registration Statement or, with respect to an amendment or a supplement, if such
Holder's Registrable Securities are included in such Registration Statement
(each an "INFORMATION REQUEST"). Provided that the Company shall have complied
with its obligations set forth in the preceding sentence, it shall be a
condition precedent to the obligations of the Company to complete the
registration pursuant to this Agreement with respect to the Registrable
Securities of a particular Holder that such Holder shall furnish to the Company,
in response to an Information Request, such information regarding itself, the
Registrable Securities held by it and the intended method of disposition of the
Registrable Securities held by it as shall be reasonably required to effect the
registration of such Registrable Securities and shall execute such documents in
connection with such registration as the Company may reasonably request.

                  b. Each Holder, by such Holder's acceptance of the Registrable
Securities, agrees to cooperate with the Company as reasonably requested by the
Company in connection with the preparation and filing of any Registration
Statement hereunder, unless such Holder has notified the Company in writing of
such Holder's election to exclude all of such Holder's Registrable Securities
from such Registration Statement.

                  c. Each Holder agrees that, upon receipt of any notice from
the Company of the happening of any event of the kind described in Section 3(g)
or the first sentence of 3(f) or written notice from the company of a Grace
Period, such Holder will immediately discontinue disposition of Registrable
Securities pursuant to any Registration Statement(s) covering such Registrable
Securities until such Holder's receipt of the copies of the supplemented or
amended prospectus contemplated by Section 3(g) or the first sentence of 3(f) or
receipt of notice that no supplement or amendment is required or that the Grace
Period has ended. Notwithstanding anything to the contrary, the Company shall
cause its transfer agent to deliver unlegended shares of Common Stock to a
transferee of a Holder in accordance with the terms of the Warrant Agreement in
connection with any sale of Registrable Securities with respect to which a
Holder has entered into a contract for sale prior to the Holder's receipt of a
notice from the Company of the happening of any event of the kind described in
Section 3(g) or the first sentence of 3(f) and for which the Holder has not yet
settled.


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<PAGE>

         5. EXPENSES OF REGISTRATION.

                  All reasonable expenses, other than underwriting discounts and
commissions and the fees and expenses of Legal Counsel or other legal and
professional advisors to any Holder, incurred in connection with registrations,
filings or qualifications pursuant to Sections 2 and 3, including, without
limitation, all registration, listing and qualifications fees, printers and
accounting fees, and fees and disbursements of counsel for the Company shall be
paid by the Company.

         6. INDEMNIFICATION.

                  In the event any Registrable Securities are included in a
Registration Statement under this Agreement:

                  a. To the fullest extent permitted by law, the Company will,
and hereby does, indemnify, hold harmless and defend each Holder, the directors,
officers, partners, employees, agents, representatives of, and each Person, if
any, who controls any Holder within the meaning of the 1933 Act or the 1934 Act
(each, an "INDEMNIFIED PERSON"), against any losses, claims, damages,
liabilities, judgments, fines, penalties, charges, costs, reasonable attorneys'
fees, amounts paid in settlement or expenses, joint or several, (collectively,
"CLAIMS") incurred in investigating, preparing or defending any action, claim,
suit, inquiry, proceeding, investigation or appeal taken from the foregoing by
or before any court or governmental, administrative or other regulatory agency,
body or the SEC, whether pending or threatened, whether or not an indemnified
party is or may be a party thereto ("INDEMNIFIED DAMAGES"), to which any of them
may become subject insofar as such Claims (or actions or proceedings, whether
commenced or threatened, in respect thereof) arise out of or are based upon: (i)
any untrue statement or alleged untrue statement of a material fact in a
Registration Statement or any post-effective amendment thereto or in any filing
made in connection with the qualification of the offering under the securities
or other "blue sky" laws of any jurisdiction in which Registrable Securities are
offered ("BLUE SKY FILING"), or the omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading, (ii) any untrue statement or alleged untrue statement of
a material fact contained in any preliminary prospectus if used prior to the
effective date of such Registration Statement, or contained in the final
prospectus (as amended or supplemented, if the Company files any amendment
thereof or supplement thereto with the SEC) or the omission or alleged omission
to state therein any material fact necessary to make the statements made
therein, in light of the circumstances under which the statements therein were
made, not misleading, (iii) any violation or alleged violation by the Company of
the 1933 Act, the 1934 Act, any other law, including, without limitation, any
state securities law, or any rule or regulation thereunder relating to the offer
or sale of the Registrable Securities pursuant to a Registration Statement or
(iv) any material violation of this Agreement by the Company (the matters in the
foregoing clauses (i) through (iv) being, collectively, "VIOLATIONS"). Subject
to Section 6(c), the Company shall reimburse the Indemnified Persons, promptly
as such expenses are incurred and are due and payable, for any legal fees or
other reasonable expenses incurred by them in connection with investigating or
defending any such Claim. Notwithstanding anything to the contrary contained
herein, the indemnification agreement contained in this Section 6(a): (i) shall
not apply to a Claim by an Indemnified Person arising out of or based upon a
Violation which occurs in reliance upon and in conformity with information
furnished in writing to the Company by such Indemnified Person for such
Indemnified Person expressly for use in connection with the preparation of the
Registration Statement or any such amendment thereof or supplement thereto; (ii)
with respect to





                                       10
<PAGE>

any preliminary prospectus, shall not inure to the benefit of any such person
from whom the person asserting any such Claim purchased the Registrable
Securities that are the subject thereof (or to the benefit of any person
controlling such person) if the untrue statement or omission of material fact
contained in the preliminary prospectus was corrected in the prospectus, as then
amended or supplemented, if such prospectus was timely made available by the
Company pursuant to Section 3(d), and the Indemnified Person was promptly
advised in writing not to use the incorrect prospectus prior to the use giving
rise to a violation and such Indemnified Person, notwithstanding such advice,
used it; (iii) shall not be available to the extent such Claim is based on a
failure of the Holder to deliver or to cause to be delivered the prospectus made
available by the Company, if such prospectus was timely made available by the
Company pursuant to Section 3(d); and (iv) shall not apply to amounts paid in
settlement of any Claim if such settlement is effected without the prior written
consent of the Company, which consent shall not be unreasonably withheld. Such
indemnity shall remain in full force and effect regardless of any investigation
made by or on behalf of the Indemnified Person and shall survive the transfer of
the Registrable Securities by the Holders pursuant to Section 9.

                  b. In connection with any Registration Statement in which a
Holder is participating, each such Holder agrees to severally and not jointly
indemnify, hold harmless and defend, to the same extent and in the same manner
as is set forth in Section 6(a), the Company, each of its directors, employees,
agents and representatives, each of its officers who signs the Registration
Statement, each Person, if any, who controls the Company within the meaning of
the 1933 Act or the 1934 Act (each an "INDEMNIFIED PARTY"), against any Claim or
Indemnified Damages to which any of them may become subject, under the 1933 Act,
the 1934 Act or otherwise, insofar as such Claim or Indemnified Damages arise
out of or are based upon any Violation, in each case to the extent, and only to
the extent, that such Violation occurs in reliance upon and in conformity with
written information furnished to the Company by such Holder expressly for use in
connection with such Registration Statement; and, subject to Section 6(c), such
Holder will reimburse any legal or other expenses reasonably incurred by an
Indemnified Party in connection with investigating or defending any such Claim;
provided, however, that the indemnity agreement contained in this Section 6(b)
and the agreement with respect to contribution contained in Section 7 shall not
apply to amounts paid in settlement of any Claim if such settlement is effected
without the prior written consent of such Holder, which consent shall not be
unreasonably withheld; provided, further, however, that the Holder shall be
liable under this Section 6(b) for only that amount of a Claim or Indemnified
Damages as does not exceed the net proceeds to such Holder as a result of the
sale of Registrable Securities pursuant to such Registration Statement. Such
indemnity shall remain in full force and effect regardless of any investigation
made by or on behalf of such Indemnified Party and shall survive the transfer of
the Registrable Securities by the Holders pursuant to Section 9. Notwithstanding
anything to the contrary contained herein, the indemnification agreement
contained in this Section 6(b) with respect to any preliminary prospectus shall
not inure to the benefit of any Indemnified Party if the untrue statement or
omission of material fact contained in the preliminary prospectus was corrected
on a timely basis in the prospectus, as then amended or supplemented.

                  c. Promptly after receipt by an Indemnified Person or
Indemnified Party under this Section 6 of notice of the commencement of any
action or proceeding (including any governmental action or proceeding) involving
a Claim, such Indemnified Person or Indemnified Party shall, if a Claim in
respect thereof is to be made against any indemnifying party under this Section
6, deliver to the indemnifying party a written notice of the commencement
thereof, and the indemnifying party shall have the right to participate in, and,
to the extent the indemnifying party so desires, jointly with any other
indemnifying party similarly noticed, to assume control of




                                       11
<PAGE>

the defense thereof with counsel mutually satisfactory to the indemnifying party
and the Indemnified Person or the Indemnified Party, as the case may be;
provided, however, that an Indemnified Person or Indemnified Party shall have
the right to retain its own counsel with the fees and expenses of not more than
one counsel for such Indemnified Person or Indemnified Party to be paid by the
indemnifying party, if, in the reasonable opinion of counsel retained by the
indemnifying party, the representation by such counsel of the Indemnified Person
or Indemnified Party and the indemnifying party would be inappropriate due to
actual or potential differing interests between such Indemnified Person or
Indemnified Party and any other party represented by such counsel in such
proceeding. In the case of an Indemnified Person, legal counsel referred to in
the immediately preceding sentence shall be selected by the Holders holding at
least two-thirds (2/3) in interest of the Registrable Securities included in the
Registration Statement to which the Claim relates. The Indemnified Party or
Indemnified Person shall cooperate fully with the indemnifying party in
connection with any negotiation or defense of any such action or Claim by the
indemnifying party and shall furnish to the indemnifying party all information
reasonably available to the Indemnified Party or Indemnified Person which
relates to such action or Claim. The indemnifying party shall keep the
Indemnified Party or Indemnified Person fully apprised at all times as to the
status of the defense or any settlement negotiations with respect thereto. No
indemnifying party shall be liable for any settlement of any action, claim or
proceeding effected without its prior written consent, provided, however, that
the indemnifying party shall not unreasonably withhold, delay or condition its
consent. No indemnifying party shall, without the prior written consent of the
Indemnified Party or Indemnified Person, consent to entry of any judgment or
enter into any settlement or other compromise that imposes obligations on the
Indemnified Party or the Indemnified Person, respectively, and which does not
include as an unconditional term thereof the giving by the claimant or plaintiff
to such Indemnified Party or Indemnified Person of a release from all liability
in respect to such Claim or litigation. Following indemnification as provided
for hereunder, the indemnifying party shall be subrogated to all rights of the
Indemnified Party or Indemnified Person with respect to all third parties, firms
or corporations relating to the matter for which indemnification has been made.
The failure to deliver written notice to the indemnifying party within a
reasonable time of the commencement of any such action shall not relieve such
indemnifying party of any liability to the Indemnified Person or Indemnified
Party under this Section 6, except to the extent that the indemnifying party is
prejudiced in its ability to defend such action.

                  d. The indemnification required by this Section 6 shall be
made by periodic payments of the amount thereof during the course of the
investigation or defense, as and when bills are received or Indemnified Damages
are incurred.

                  e. The indemnity agreements contained herein shall be in
addition to (i) any cause of action or similar right of the Indemnified Party or
Indemnified Person against the indemnifying party or others, and (ii) any
liabilities the indemnifying party may be subject to pursuant to the law.

         7. CONTRIBUTION.

                  To the extent any indemnification by an indemnifying party is
prohibited or limited by law, the indemnifying party agrees to make the maximum
contribution with respect to any amounts for which it would otherwise be liable
under Section 6 to the fullest extent permitted by law; provided, however, that:
(i) no Person involved in the sale of Registrable Securities which Person is
guilty of fraudulent misrepresentation (within the meaning of Section


                                       12
<PAGE>

11(f) of the 1933 Act) in connection with such sale, shall be entitled to
contribution from any Person involved in such sale of Registrable Securities who
was not guilty of fraudulent misrepresentation; and (ii) contribution by any
seller of Registrable Securities shall be limited in amount to the net amount of
proceeds received by such seller from the sale of such Registrable Securities
pursuant to such Registration Statement.

         8. REPORTS UNDER THE 1934 ACT.

                  With a view to making available to the Holders the benefits of
Rule 144 promulgated under the 1933 Act or any other similar rule or regulation
of the SEC that may at any time permit the Holders to sell securities of the
Company to the public without registration ("RULE 144"), the Company agrees to:

                  a. make and keep public information available, as those terms
are understood and defined in Rule 144;

                  b. file with the SEC in a timely manner all reports and other
documents required of the Company under the 1933 Act and the 1934 Act so long as
the Company remains subject to such requirements (it being understood that
nothing herein shall limit the Company's obligations under Section 4(c) of the
Warrant Agreement) and the filing of such reports and other documents is
required for the applicable provisions of Rule 144; and

                  c. furnish to each Holder so long as such Holder owns
Registrable Securities, promptly upon request, (i) a written statement by the
Company that it has complied with the reporting requirements of Rule 144, the
1933 Act and the 1934 Act, (ii) a copy of the most recent annual or quarterly
report of the Company and such other reports and documents so filed by the
Company, and (iii) such other information as may be reasonably requested to
permit the Holders to sell such securities pursuant to Rule 144 without
registration.

         9. ASSIGNMENT OF REGISTRATION RIGHTS.

                  The rights under this Agreement shall be automatically
assignable by the Holders to any transferee of all or any portion of Registrable
Securities if: (i) the Holder agrees in writing with the transferee or assignee
to assign such rights, and a copy of such agreement is furnished to the Company
within a reasonable time after such transfer or assignment; (ii) the Company is,
within a reasonable time after such transfer or assignment, furnished with
written notice of (a) the name and address of such transferee or assignee, and
(b) the securities with respect to which such registration rights are being
transferred or assigned; (iii) immediately following such transfer or assignment
the further disposition of such securities by the transferee or assignee is
restricted under the 1933 Act and applicable state securities laws; (iv) at or
before the time the Company receives the written notice contemplated by clause
(ii) of this sentence the transferee or assignee agrees in writing with the
Company to be bound by all of the provisions contained herein; and (v) such
transfer shall have been made in accordance with the applicable requirements of
the Warrant Agreement.

         10. AMENDMENT OF REGISTRATION RIGHTS.

                  Provisions of this Agreement may be amended and the observance
thereof may be waived (either generally or in a particular instance and either
retroactively or prospectively), only with the written consent of the Company
and the Holders who then hold at least two-thirds (2/3)



                                       13
<PAGE>
of the Registrable Securities, or, if prior to the first Closing Date (as
defined in the Warrant Agreement) to occur under the Warrant Agreement, the
Holders who purchased at least two-thirds (2/3) of the aggregate original
principal amount of the Convertible Notes (as defined in the Warrant Agreement).
Any amendment or waiver effected in accordance with this Section 10 shall be
binding upon each Holder and the Company. No such amendment shall be effective
to the extent that it applies to less than all of the holders of the Registrable
Securities. No consideration shall be offered or paid to any Person to amend or
consent to a waiver or modification of any provision of any of this Agreement
unless the same consideration also is offered to all of the parties to this
Agreement.

         11. MISCELLANEOUS.

                  a. A Person is deemed to be a holder of Registrable Securities
whenever such Person owns or is deemed to own of record such Registrable
Securities. If the Company receives conflicting instructions, notices or
elections from two or more Persons with respect to the same Registrable
Securities, the Company shall act upon the basis of instructions, notice or
election received from the registered owner of such Registrable Securities.

                  b. Any notices, consents, waivers or other communications
required or permitted to be given under the terms of this Agreement must be in
writing and will be deemed to have been delivered: (i) upon receipt, when
delivered personally; (ii) upon receipt, when sent by facsimile (provided
confirmation of transmission is mechanically or electronically generated and
kept on file by the sending party); or (iii) one (1) Business Day after deposit
with a nationally recognized overnight delivery service, in each case properly
addressed to the party to receive the same. The addresses and facsimile numbers
for such communications shall be:

                  If to the Company:

                           Zix Corporation
                           2711 N. Haskell Avenue
                           Suite 2300
                           Dallas, Texas 75204
                           Telephone:       214-370-2000
                           Facsimile:       214-515-7385
                           Attention:       General Counsel

                  With a copy to:

                           Hughes & Luce L.L.P.
                           111 Congress Avenue, 9th Floor
                           Austin, Texas 78701
                           Telephone:       512-482-6800
                           Facsimile:       512-482-6859
                           Attention:       Bryan C. Wittman, Esq.

                  If to Legal Counsel:

                           Katten Muchin Zavis Rosenman
                           525 West Monroe Street, Suite 1600
                           Chicago, Illinois 60661-3693
                           Telephone:  312-902-5200
                           Facsimile:  312-902-1061
                           Attention:  Robert J. Brantman, Esq.



                                       14
<PAGE>

If to an Investor, to its address and facsimile number set forth on the Schedule
of Investors attached hereto, with copies to such Investor's representatives as
set forth on the Schedule of Investors, or, in the case of an Investor or other
party named above, to such other address and/or facsimile number and/or to the
attention of such other person as the recipient party has specified by written
notice given to each other party five (5) days prior to the effectiveness of
such change. Written confirmation of receipt (A) given by the recipient of such
notice, consent, waiver or other communication, (B) mechanically or
electronically generated by the sender's facsimile machine containing the time,
date, recipient facsimile number and an image of the first page of such
transmission or (C) provided by a courier or overnight courier service shall be
rebuttable evidence of personal service, receipt by facsimile or receipt from a
nationally recognized overnight delivery service in accordance with clause (i),
(ii) or (iii) above, respectively.

                  c. Failure of any party to exercise any right or remedy under
this Agreement or otherwise, or delay by a party in exercising such right or
remedy, shall not operate as a waiver thereof.

                  d. All questions concerning the construction, validity,
enforcement and interpretation of this Agreement shall be governed by the
internal laws of the State of New York, without giving effect to any choice of
law or conflict of law provision or rule (whether of the State of New York or
any other jurisdictions) that would cause the application of the laws of any
jurisdictions other than the State of New York. Each party hereby irrevocably
submits to the exclusive jurisdiction of the state and federal courts sitting
the City of New York, borough of Manhattan, for the adjudication of any dispute
hereunder or in connection herewith or with any transaction contemplated hereby
or discussed herein, and hereby irrevocably waives, and agrees not to assert in
any suit, action or proceeding, any claim that it is not personally subject to
the jurisdiction of any such court, that such suit, action or proceeding is
brought in an inconvenient forum or that the venue of such suit, action or
proceeding is improper. Each party hereby irrevocably waives personal service of
process and consents to process being served in any such suit, action or
proceeding by mailing a copy thereof to such party at the address for such
notices to it under this Agreement and agrees that such service shall constitute
good and sufficient service of process and notice thereof. Nothing contained
herein shall be deemed to limit in any way any right to serve process in any
manner permitted by law. If any provision of this Agreement shall be invalid or
unenforceable in any jurisdiction, such invalidity or unenforceability shall not
affect the validity or enforceability of the remainder of this Agreement in that
jurisdiction or the validity or enforceability of any provision of this
Agreement in any other jurisdiction. EACH PARTY HEREBY IRREVOCABLY WAIVES ANY
RIGHT IT MAY HAVE, AND AGREES NOT TO REQUEST, A JURY TRIAL FOR THE ADJUDICATION
OF ANY DISPUTE HEREUNDER OR IN CONNECTION HEREWITH OR ARISING OUT OF THIS
AGREEMENT OR ANY TRANSACTION CONTEMPLATED HEREBY.

                  e. This Agreement, the Warrant Agreement and the Replacement
Warrants constitute the entire agreement among the parties hereto with respect
to the subject matter hereof and thereof. There are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein and
therein. Except for the Initial Transaction Documents (as defined in the Warrant
Agreement), this Agreement, the Warrant Agreement and the Replacement Warrants
supersede all prior agreements and understandings among the parties hereto with


                                       15
<PAGE>

respect to the subject matter hereof and thereof.

                  f. Subject to the requirements of Section 9, this Agreement
shall inure to the benefit of and be binding upon the permitted successors and
assigns of each of the parties hereto.

                  g. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

                  h. This Agreement may be executed in identical counterparts,
each of which shall be deemed an original but all of which shall constitute one
and the same agreement. This Agreement, once executed by a party, may be
delivered to the other party hereto by facsimile transmission of a copy of this
Agreement bearing the signature of the party so delivering this Agreement.

                  i. Each party shall do and perform, or cause to be done and
performed, all such further acts and things, and shall execute and deliver all
such other agreements, certificates, instruments and documents, as the other
party may reasonably request in order to carry out the intent and accomplish the
purposes of this Agreement and the consummation of the transactions contemplated
hereby.

                  j. All consents and other determinations to be made by the
Holders pursuant to this Agreement shall be made, unless otherwise specified in
this Agreement, by Holders holding at least two-thirds (2/3) of the Registrable
Securities, determined as if all of the Replacement Warrants then outstanding
have been converted into or exercised for Registrable Securities without regard
to any limitations on the exercise of the Replacement Warrants.

                  k. The language used in this Agreement will be deemed to be
the language chosen by the parties to express their mutual intent and no rules
of strict construction will be applied against any party.

                  l. This Agreement is intended for the benefit of the parties
hereto and their respective permitted successors and assigns, and is not for the
benefit of, nor may any provision hereof be enforced by, any other Person.

                                   * * * * * *



                                       16
<PAGE>
         IN WITNESS WHEREOF, the parties have caused this Registration Rights
Agreement to be duly executed as of day and year first above written.

COMPANY:                                INVESTORS:

ZIX CORPORATION                         HFTP INVESTMENT L.L.C.
                                        By:  Promethean Asset Management L.L.C.
                                        Its: Investment Manager
By:   /s/ RONALD A. WOESSNER
      -----------------------------
      Name: Ronald A. Woessner
      Title: SVP                        By:  /s/ JAMES F. O'BRIEN, JR.
                                           ------------------------------------
                                           Name: James F. O'Brien, Jr.
                                           Title: Managing Member

                                        GAIA OFFSHORE MASTER FUND, LTD.
                                        By:  Promethean Asset Management L.L.C.
                                        Its: Investment Manager


                                        By:  /s/ JAMES F. O'BRIEN, JR.
                                           ------------------------------------
                                           Name: James F. O'Brien, Jr.
                                           Title: Managing Member

                                        CAERUS FUND LTD.
                                        By:  Promethean Asset Management L.L.C.
                                        Its: Investment Manager


                                        By:  /s/ JAMES F. O'BRIEN, JR.
                                           ------------------------------------
                                           Name: James F. O'Brien, Jr.
                                           Title: Managing Member



<PAGE>

                              SCHEDULE OF INVESTORS

<Table>
<Caption>

                                                         HOLDER ADDRESS                         HOLDER'S LEGAL REPRESENTATIVES'
            HOLDER'S NAME                             AND FACSIMILE NUMBER                       ADDRESS AND FACSIMILE NUMBER
---------------------------------------   ----------------------------------------------   ----------------------------------------

<S>                                       <C>                                              <C>
HFTP Investment L.L.C.                    c/o Promethean Asset Management L.L.C.           Promethean Investment Group, L.L.C.
                                          750 Lexington Avenue, 22nd Floor                 750 Lexington Ave., 22nd Floor
                                          New York, New York 10022                         New York, New York 10022
                                          Attention: David M. Kittay                       Attention: David M. Kittay
                                                     Greg Carney                                      Greg Carney
                                          Telephone: (212) 702-5200                        Telephone: 212-702-5200
                                          Facsimile: (212) 758-9334                        Facsimile: 212-758-9334

                                                                                           Katten Muchin Zavis Rosenman
                                                                                           525 W. Monroe Street
                                                                                           Chicago, Illinois 60661-3693
                                                                                           Attention: Robert J. Brantman, Esq.
                                                                                           Telephone: (312) 902-5200
                                                                                           Facsimile: (312) 902-1061

Gaia Offshore Master Fund, Ltd.           c/o Promethean Asset Management L.L.C.           Promethean Investment Group, L.L.C.
                                          750 Lexington Avenue, 22nd Floor                 750 Lexington Ave., 22nd Floor
                                          New York, New York 10022                         New York, New York 10022
                                          Attention: David M. Kittay                       Attention: David M. Kittay
                                                     Greg Carney                                      Greg Carney
                                          Telephone: (212) 702-5200                        Telephone: 212-702-5200
                                          Facsimile: (212) 758-9334                        Facsimile: 212-758-9334

                                                                                           Katten Muchin Zavis Rosenman
                                                                                           525 W. Monroe Street
                                                                                           Chicago, Illinois 60661-3693
                                                                                           Attention: Robert J. Brantman, Esq.
                                                                                           Telephone: (312) 902-5200
                                                                                           Facsimile: (312) 902-1061

Caerus Fund Ltd.                          c/o Promethean Asset Management L.L.C.           Promethean Investment Group, L.L.C.
                                          750 Lexington Avenue, 22nd Floor                 750 Lexington Ave., 22nd Floor
                                          New York, New York 10022                         New York, New York 10022
                                          Attention: David M. Kittay                       Attention: David M. Kittay
                                                     Greg Carney                                      Greg Carney
                                          Telephone: (212) 702-5200                        Telephone: 212-702-5200
                                          Facsimile: (212) 758-9334                        Facsimile: 212-758-9334

                                                                                           Katten Muchin Zavis Rosenman
                                                                                           525 W. Monroe Street
                                                                                           Chicago, Illinois 60661-3693
                                                                                           Attention: Robert J. Brantman, Esq.
                                                                                           Telephone: (312) 902-5200
                                                                                           Facsimile: (312) 902-1061

</Table>



<PAGE>
                                                                       EXHIBIT A

                         FORM OF NOTICE OF EFFECTIVENESS
                            OF REGISTRATION STATEMENT
[TRANSFER AGENT]
ATTN:
     -------------------------------

                  RE: ZIX CORPORATION

Ladies and Gentlemen:

         We are counsel to Zix Corporation, a Texas corporation (the "COMPANY"),
and have represented the Company in connection with that certain Agreement
Regarding Exercise and Issuance of Warrants (the "AGREEMENT") entered into by
and among the Company and the investors named therein (collectively, the
"HOLDERS") pursuant to which the Company issued to the Holders warrants to
purchase an aggregate of _________ shares of the Company's common stock, $0.01
par value per share (the "COMMON STOCK"), subject to adjustment (the
"REPLACEMENT WARRANTS"). Pursuant to the Agreement, the Company also has entered
into a Registration Rights Agreement with the Holders (the "NEW REGISTRATION
RIGHTS AGREEMENT") pursuant to which the Company agreed, among other things, to
register the Registrable Securities (as defined in the New Registration Rights
Agreement), including the shares of Common Stock issuable upon exercise of the
Replacement Warrants, under the Securities Act of 1933, as amended (the "1933
ACT"). In connection with the Company's obligations under the Registration
Rights Agreement, on ____________ ___, 200_, the Company filed a Registration
Statement on Form S-3 (File No. 333-__________) (the "REGISTRATION STATEMENT")
with the Securities and Exchange Commission (the "SEC") relating to the
Registrable Securities which names each of the Holders as a selling stockholder
thereunder.

         In connection with the foregoing, we advise you that a member of the
SEC's staff has advised us by telephone that the SEC has entered an order
declaring the Registration Statement effective under the 1933 Act at [ENTER TIME
OF EFFECTIVENESS] on [ENTER DATE OF EFFECTIVENESS] and we have no knowledge,
after telephonic inquiry of a member of the SEC's staff, that any stop order
suspending its effectiveness has been issued or that any proceedings for that
purpose are pending before, or threatened by, the SEC and the Registrable
Securities are available for resale under the 1933 Act pursuant to the
Registration Statement.

                                          Very truly yours,

                                          [ISSUER'S COUNSEL]

                                          By:
                                             -------------------------
cc: [LIST NAMES OF HOLDERS]