<PAGE>

                                                                     EXHIBIT 4.3

                          REGISTRATION RIGHTS AGREEMENT

                  This Registration Rights Agreement (this "AGREEMENT") is made
and entered into as of June 24, 2003, by and among Zix Corporation, a Texas
corporation (the "COMPANY"), and the investors signatory hereto (each a
"PURCHASER" and collectively, the "PURCHASERS").

                  This Agreement is made pursuant to the Securities Purchase
Agreement, dated as of the date hereof among the Company and the Purchasers (the
"PURCHASE AGREEMENT").

                  The Company and the Purchasers hereby agree as follows:

         1.       Definitions. Capitalized terms used and not otherwise defined
herein that are defined in the Purchase Agreement shall have the meanings given
such terms in the Purchase Agreement. As used in this Agreement, the following
terms shall have the following meanings:

                  "EFFECTIVE DATE" means the date that the Registration
Statement is first declared effective by the Commission.

                  "EFFECTIVENESS DATE" means the earlier of (a) the 90th day
following the Closing Date, and (b) the fifth Trading Day following the date on
which the Company is notified by the Commission that the Registration Statement
will not be reviewed or is no longer subject to further review and comments.

                  "EFFECTIVENESS PERIOD" shall have the meaning set forth in
Section 2(a).

                  "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

                  "FILING DATE" means the 30th day following the Closing Date.

                  "HOLDER" or "HOLDERS" means the holder or holders, as the case
may be, from time to time of Registrable Securities.

                  "INDEMNIFIED PARTY" shall have the meaning set forth in
Section 5(c).

                  "INDEMNIFYING PARTY" shall have the meaning set forth in
Section 5(c).

                  "LOSSES" shall have the meaning set forth in Section 5(a).

                  "NEW WARRANTS" shall have the meaning set forth in the
Warrants.

                  "PROCEEDING" means an action, claim, suit, investigation or
proceeding (including, without limitation, an investigation or partial
proceeding, such as a deposition), whether commenced or threatened.

                  "PROSPECTUS" means the prospectus included in a Registration
Statement (including, without limitation, a prospectus that includes any
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A promulgated under the
Securities Act), as amended or supplemented by any prospectus

                                                   Registration Rights Agreement

<PAGE>

supplement, with respect to the terms of the offering of any portion of the
Registrable Securities covered by the Registration Statement, and all other
amendments and supplements to the Prospectus, including post-effective
amendments, and all material incorporated by reference or deemed to be
incorporated by reference in such Prospectus.

                  "REGISTRABLE SECURITIES" means (i) the Shares, and (ii) the
shares of Common Stock issuable upon exercise of the Warrants.

                  "REGISTRATION STATEMENT" means the registration statement
required to be filed hereunder in accordance with Section 2, including (in each
case) the Prospectus, amendments and supplements to such registration statement
or Prospectus, including pre- and post-effective amendments, all exhibits
thereto, and all material incorporated by reference or deemed to be incorporated
by reference in such registration statement.

                  "RULE 144" means Rule 144 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to time,
or any similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

                  "RULE 415" means Rule 415 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to time,
or any similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

                  "RULE 424" means Rule 424 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to time,
or any similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

                  "SECURITIES ACT" means the Securities Act of 1933, as amended.

                  "SHARES" means the shares of Common Stock issued or issuable
to the Purchasers pursuant to the Purchase Agreement.

                  "SPECIAL COUNSEL" means Bryan Cave LLP.

                  "WARRANTS" means (i) the Warrants issued or issuable under the
Purchase Agreement, and (ii) any New Warrants issuable under the Warrants.

         2.       Registration.

                  (a)      On or prior to the Filing Date, the Company shall
prepare and file with the Commission a Registration Statement covering the
resale of all Registrable Securities not already covered by an existing and
effective Registration Statement for an offering to be made on a continuous
basis pursuant to Rule 415. The Registration Statement shall be on Form S-3
(except if the Company is not then eligible to register for resale the
Registrable Securities on Form S-3, in which case such registration shall be on
another appropriate form in accordance herewith) and shall contain (except if
otherwise agreed by the Holders) the "Plan of Distribution" attached hereto as
Annex A. The Company shall cause the Registration Statement to be declared
effective

                                                   Registration Rights Agreement

                                      -2-

<PAGE>

under the Securities Act as soon as possible but, in any event, no later than
the Effectiveness Date, and shall use its best efforts to keep the Registration
Statement continuously effective under the Securities Act until the date which
is four years after the date that the Registration Statement is declared
effective by the Commission or such earlier date when all Registrable Securities
covered by the Registration Statement have been sold or may be sold without
volume restrictions pursuant to Rule 144(k) as determined by the counsel to the
Company pursuant to a written opinion letter to such effect, addressed and
acceptable to the Company's transfer agent and the affected Holders (the
"EFFECTIVENESS PERIOD").

                  (b)      If: (i) the Registration Statement is not filed on or
prior to the Filing Date (if the Company files the Registration Statement
without affording the Holders the opportunity to review and comment on the same
as required by Section 3(a) hereof, the Company shall not be deemed to have
satisfied this clause (i)), or (ii) the Company fails to file with the
Commission a request for acceleration in accordance with Rule 461 promulgated
under the Securities Act, within five Trading Days of the date that the Company
is notified (orally or in writing, whichever is earlier) by the Commission that
the Registration Statement will not be "reviewed," or not subject to further
review, or (iii) the Company fails to respond to any comments made by the
Commission within ten days after the receipt of such comments, or (iv) after the
Effective Date, the Registration Statement ceases to be effective and available
to the Holders thereunder as to all of the Registrable Securities (whether upon
the delivery of an Advice pursuant to Section 6(d) or otherwise) at any time
prior to the expiration of its Effectiveness Period without being succeeded
within fifteen Trading Days by an effective amendment thereto or by a subsequent
Registration Statement filed with and declared effective by the Commission or a
written notification from the Company that such Registration Statement is
effective and available and no amendment thereto is required, or (v) an
amendment to the Registration Statement is not filed by the Company with the
Commission within fifteen Trading Days of the Commission's notifying the Company
that such amendment is required in order for the Registration Statement to be
declared effective, or (vi) the exercise rights of the Holders pursuant to the
Warrants are suspended for any reason, or (vii) the Registration Statement shall
not be declared effective by the Commission on or prior to the Effectiveness
Date (any such failure or breach being referred to as an "EVENT," and for
purposes of clause (i), (vi) or (vii) the date on which such Event occurs, or
for purposes of clause (ii) the date on which such five Trading Day period is
exceeded, or for purposes of clause (iii) the date which such ten day-period is
exceeded, of for purposes of clauses (iv) or (v) the date which such fifteen
Trading Day-period is exceeded, being referred to as "EVENT DATE"), then, in
addition to any other rights available to the Holders: (x) on each such Event
Date the Company shall pay to each Holder an amount in cash, as liquidated
damages and not as a penalty, equal to 1% of the aggregate purchase price paid
by such Holder pursuant to the Purchase Agreement; and (y) on each monthly
anniversary of each such Event Date thereof (if the applicable Event shall not
have been cured by such date) until the applicable Event is cured, the Company
shall pay to each Holder an amount in cash, as liquidated damages and not as a
penalty, equal to 1% of the aggregate purchase price paid by such Holder
pursuant to the Purchase Agreement. If the Company fails to pay any liquidated
damages pursuant to this Section in full within seven days after the date
payable, the Company will pay interest thereon at a rate of 18% per annum (or
such lesser maximum amount that is permitted to be paid by applicable law) to
the Holder, accruing daily from the date such liquidated damages are due until
such amounts, plus all such interest thereon, are paid in full. The liquidated
damages pursuant to the terms hereof shall apply on a pro rata basis for any
portion of a month prior to the cure of an Event.

                                                   Registration Rights Agreement

                                      -3-

<PAGE>

                  (c)      Notwithstanding anything herein to the contrary, the
Company shall prepare and file a supplement to the Registration Statement (if
permitted for such purpose under the Securities Act) within 5 Trading Days
following the issuance of a New Warrant, or (if such supplement is not permitted
for such purposes under the Securities Act), a new Registration Statement within
15 Trading Days following the issuance of a New Warrant.

         3.       Registration Procedures

                  In connection with the Company's registration obligations
hereunder, the Company shall:

                  (a)      Not less than two Trading Days prior to the filing of
the Registration Statement or any related Prospectus or any amendment or
supplement thereto, the Company shall, (i) furnish to the Holders and the
Special Counsel copies of all such documents proposed to be filed which
documents will be subject to the review of such Holders and the Special Counsel,
and (ii) cause its officers and directors, counsel and independent certified
public accountants to respond to such inquiries as shall be necessary, in the
reasonable opinion of the Special Counsel to conduct a reasonable investigation
within the meaning of the Securities Act. The Company shall not file the
Registration Statement or any such Prospectus or any amendments or supplements
thereto to which the Holders of a majority of the Registrable Securities or the
Special Counsel shall reasonably object in good faith.

                  (b)      (i) Prepare and file with the Commission such
amendments, including post-effective amendments, to the Registration Statement
and the Prospectus used in connection therewith as may be necessary to keep the
Registration Statement continuously effective as to the applicable Registrable
Securities for the Effectiveness Period and prepare and file with the Commission
such additional Registration Statements in order to register for resale under
the Securities Act all of the Registrable Securities; (ii) cause the related
Prospectus to be amended or supplemented by any required Prospectus supplement,
and as so supplemented or amended to be filed pursuant to Rule 424; (iii)
respond as promptly as reasonably possible, and in any event within ten days, to
any comments received from the Commission with respect to the Registration
Statement or any amendment thereto and, as promptly as reasonably possible
provide the Holders true and complete copies of all correspondence from and to
the Commission relating to the Registration Statement; and (iv) comply in all
material respects with the provisions of the Securities Act and the Exchange Act
with respect to the disposition of all Registrable Securities covered by the
Registration Statement during the applicable period in accordance with the
intended methods of disposition by the Holders thereof set forth in the
Registration Statement as so amended or in such Prospectus as so supplemented.

                  (c)      Notify the Holders of Registrable Securities to be
sold and the Special Counsel as promptly as reasonably possible (and, in the
case of (i)(A) below, not less than three Trading Days prior to such filing) and
(if requested by any such Person) confirm such notice in writing no later than
one Trading Day following the day (i)(A) when a Prospectus or any Prospectus
supplement or post-effective amendment to the Registration Statement is proposed
to be filed; (B) when the Commission notifies the Company whether there will be
a "review" of such Registration Statement and whenever the Commission comments
in writing on such Registration Statement (the Company shall provide true and
complete copies thereof and all

                                                   Registration Rights Agreement

                                      -4-

<PAGE>

written responses thereto to each of the Holders); and (C) with respect to the
Registration Statement or any post-effective amendment, when the same has become
effective; (ii) of any request by the Commission or any other Federal or state
governmental authority for amendments or supplements to the Registration
Statement or Prospectus or for additional information; (iii) of the issuance by
the Commission of any stop order suspending the effectiveness of the
Registration Statement covering any or all of the Registrable Securities or the
initiation of any Proceedings for that purpose; (iv) of the receipt by the
Company of any notification with respect to the suspension of the qualification
or exemption from qualification of any of the Registrable Securities for sale in
any jurisdiction, or the initiation or threatening of any Proceeding for such
purpose; and (v) of the occurrence of any event or passage of time that makes
the financial statements included in the Registration Statement ineligible for
inclusion therein or any statement made in the Registration Statement or
Prospectus or any document incorporated or deemed to be incorporated therein by
reference untrue in any material respect or that requires any revisions to the
Registration Statement, Prospectus or other documents so that, in the case of
the Registration Statement or the Prospectus, as the case may be, it will not
contain any untrue statement of a material fact or omit to state any 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.

                  (d)      Use its best efforts to avoid the issuance of, or, if
issued, obtain the withdrawal of (i) any order suspending the effectiveness of
the Registration Statement, or (ii) any suspension of the qualification (or
exemption from qualification) of any of the Registrable Securities for sale in
any jurisdiction, at the earliest practicable moment.

                  (e)      Furnish to each Holder, without charge, at least one
conformed copy of each Registration Statement and each amendment thereto,
including financial statements and schedules, all documents incorporated or
deemed to be incorporated therein by reference, and all exhibits to the extent
requested by such Person (including those previously furnished or incorporated
by reference) promptly after the filing of such documents with the Commission.

                  (f)      Promptly deliver to each Holder, without charge, as
many copies of the Prospectus or Prospectuses (including each form of
prospectus) and each amendment or supplement thereto as such Persons may
reasonably request. The Company hereby consents to the use of such Prospectus
and each amendment or supplement thereto by each of the selling Holders in
connection with the offering and sale of the Registrable Securities covered by
such Prospectus and any amendment or supplement thereto.

                  (g)      Prior to any public offering of Registrable
Securities, use its best efforts to register or qualify or cooperate with the
selling Holders in connection with the registration or qualification (or
exemption from such registration or qualification) of such Registrable
Securities for offer and sale under the securities or Blue Sky laws of such
jurisdictions within the United States as any Holder requests in writing, to
keep each such registration or qualification (or exemption therefrom) effective
during the Effectiveness Period and to do any and all other acts or things
necessary or advisable to enable the disposition in such jurisdictions of the
Registrable Securities covered by the Registration Statement; provided, that the
Company shall not be required to qualify generally to do business in any
jurisdiction where it is not then so qualified or subject the Company to any
material tax in any such jurisdiction where it is not then so subject.

                                                   Registration Rights Agreement

                                      -5-

<PAGE>

                  (h)      Cooperate with the Holders to facilitate the timely
preparation and delivery of certificates representing Registrable Securities to
be delivered to a transferee pursuant to the Registration Statement, which
certificates shall be free, to the extent permitted by the Purchase Agreement,
of all restrictive legends, and to enable such Registrable Securities to be in
such denominations and registered in such names as any such Holders may request.

                  (i)      Upon the occurrence of any event contemplated by
Section 3(c)(v), as promptly as reasonably possible, prepare a supplement or
amendment, including a post-effective amendment, to the Registration Statement
or a supplement to the related Prospectus or any document incorporated or deemed
to be incorporated therein by reference, and file any other required document so
that, as thereafter delivered, neither the Registration Statement nor such
Prospectus will contain an 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 under which they were made,
not misleading.

                  (j)      Comply with all applicable rules and regulations of
the Commission.

                  (k)      The Company may require each selling Holder to
furnish to the Company a certified statement as to the number of shares of
Common Stock beneficially owned by such Holder and, if requested by the
Commission, the controlling person thereof.

         4.       Registration Expenses. All fees and expenses incident to the
performance of or compliance with this Agreement by the Company shall be borne
by the Company whether or not any Registrable Securities are sold pursuant to
the Registration Statement. The fees and expenses referred to in the foregoing
sentence shall include, without limitation, (i) all registration and filing fees
(including, without limitation, fees and expenses (A) with respect to filings
required to be made with Nasdaq National Market or any other Trading Market, and
(B) in compliance with applicable state securities or Blue Sky laws), (ii)
printing expenses (including, without limitation, expenses of printing
certificates for Registrable Securities and of printing prospectuses if the
printing of prospectuses is reasonably requested by the holders of a majority of
the Registrable Securities included in the Registration Statement), (iii)
messenger, telephone and delivery expenses, (iv) fees and disbursements of
counsel for the Company and up to $5,000 of the fees and disbursements of
Special Counsel, (v) Securities Act liability insurance, if the Company so
desires such insurance, and (vi) fees and expenses of all other Persons retained
by the Company in connection with the consummation of the transactions
contemplated by this Agreement. In addition, the Company shall be responsible
for all of its internal expenses incurred in connection with the consummation of
the transactions contemplated by this Agreement (including, without limitation,
all salaries and expenses of its officers and employees performing legal or
accounting duties), the expense of any annual audit and the fees and expenses
incurred in connection with the listing of the Registrable Securities on any
securities exchange as required hereunder.

         5.       Indemnification

                  (a)      Indemnification by the Company. The Company shall,
notwithstanding any termination of this Agreement, indemnify and hold harmless
each Holder, the officers, directors, agents, investment advisors and employees
of each of them, each Person who controls

                                                   Registration Rights Agreement

                                      -6-

<PAGE>

any such Holder (within the meaning of Section 15 of the Securities Act or
Section 20 of the Exchange Act) and the officers, directors, agents and
employees of each such controlling Person, to the fullest extent permitted by
applicable law, from and against any and all losses, claims, damages,
liabilities, costs (including, without limitation, reasonable costs of
preparation and reasonable attorneys' fees) and expenses (collectively,
"LOSSES"), as incurred, arising out of or relating to any untrue or alleged
untrue statement of a material fact contained in the Registration Statement, any
Prospectus or any form of prospectus or in any amendment or supplement thereto
or in any preliminary prospectus, or arising out of or relating to any omission
or alleged omission of a material fact required to be stated therein or
necessary to make the statements therein (in the case of any Prospectus or form
of prospectus or supplement thereto, in light of the circumstances under which
they were made) not misleading, except to the extent, but only to the extent,
that (1) such untrue statements or omissions are based solely upon information
regarding such Holder furnished in writing to the Company by such Holder
expressly for use therein, or to the extent that such information relates to
such Holder or such Holder's proposed method of distribution of Registrable
Securities and was reviewed and expressly approved in writing by such Holder
expressly for use in the Registration Statement, such Prospectus or such form of
Prospectus or in any amendment or supplement thereto (it being understood that
the Holder has approved Annex A hereto for this purpose) or (2) in the case of
an occurrence of an event of the type specified in Section 3(c)(ii)-(v), the use
by such Holder of an outdated or defective Prospectus after the Company has
notified such Holder in writing that the Prospectus is outdated or defective and
prior to the receipt by such Holder of the Advice contemplated in Section 6(d).
The Company shall notify the Holders promptly of the institution, threat or
assertion of any Proceeding of which the Company is aware in connection with the
transactions contemplated by this Agreement.

                  (b)      Indemnification by Holders. Each Holder shall,
severally and not jointly, indemnify and hold harmless the Company, its
directors, officers, agents and employees, each Person who controls the Company
(within the meaning of Section 15 of the Securities Act and Section 20 of the
Exchange Act), and the directors, officers, agents or employees of such
controlling Persons, to the fullest extent permitted by applicable law, from and
against all Losses, as incurred, arising solely out of or based solely upon: (x)
such Holder's failure to comply with the prospectus delivery requirements of the
Securities Act or (y) any untrue statement of a material fact contained in any
Registration Statement, any Prospectus, or any form of prospectus, or in any
amendment or supplement thereto, or arising solely out of or based solely upon
any omission of a material fact required to be stated therein or necessary to
make the statements therein not misleading to the extent, but only to the
extent, that such untrue statement or omission is contained in any information
so furnished in writing by such Holder to the Company specifically for inclusion
in such Registration Statement or such Prospectus or to the extent that (1) such
untrue statements or omissions are based solely upon information regarding such
Holder furnished in writing to the Company by such Holder expressly for use
therein, or to the extent that such information relates to such Holder or such
Holder's proposed method of distribution of Registrable Securities and was
reviewed and expressly approved in writing by such Holder expressly for use in
the Registration Statement (it being understood that the Holder has approved
Annex A hereto for this purpose), such Prospectus or such form of Prospectus or
in any amendment or supplement thereto or (2) in the case of an occurrence of an
event of the type specified in Section 3(c)(ii)-(v), the use by such Holder of
an outdated or

                                                   Registration Rights Agreement

                                      -7-

<PAGE>

defective Prospectus after the Company has notified such Holder in writing that
the Prospectus is outdated or defective and prior to the receipt by such Holder
of the Advice contemplated in Section 6(d). In no event shall the liability of
any selling Holder hereunder be greater in amount than the dollar amount of the
net proceeds received by such Holder upon the sale of the Registrable Securities
giving rise to such indemnification obligation.

                  (c)      Conduct of Indemnification Proceedings. If any
Proceeding shall be brought or asserted against any Person entitled to indemnity
hereunder (an "INDEMNIFIED PARTY"), such Indemnified Party shall promptly notify
the Person from whom indemnity is sought (the "INDEMNIFYING PARTY") in writing,
and the Indemnifying Party shall assume the defense thereof, including the
employment of counsel reasonably satisfactory to the Indemnified Party and the
payment of all fees and expenses incurred in connection with defense thereof;
provided, that the failure of any Indemnified Party to give such notice shall
not relieve the Indemnifying Party of its obligations or liabilities pursuant to
this Agreement, except (and only) to the extent that it shall be determined by a
court of competent jurisdiction that such failure shall have proximately and
materially adversely prejudiced the Indemnifying Party.

                  An Indemnified Party shall have the right to employ separate
counsel in any such Proceeding and to participate in the defense thereof, but
the fees and expenses of such counsel shall be at the expense of such
Indemnified Party or Parties unless: (1) the Indemnifying Party has agreed in
writing to pay such fees and expenses; (2) the Indemnifying Party shall have
failed promptly to assume the defense of such Proceeding and to employ counsel
reasonably satisfactory to such Indemnified Party in any such Proceeding; or (3)
the named parties to any such Proceeding (including any impleaded parties)
include both such Indemnified Party and the Indemnifying Party, and such
Indemnified Party shall have been advised by counsel that a conflict of interest
is likely to exist if the same counsel were to represent such Indemnified Party
and the Indemnifying Party (in which case, if such Indemnified Party notifies
the Indemnifying Party in writing that it elects to employ separate counsel at
the expense of the Indemnifying Party, the Indemnifying Party shall not have the
right to assume the defense thereof and such counsel shall be at the expense of
the Indemnifying Party). The Indemnifying Party shall not be liable for any
settlement of any such Proceeding effected without its written consent, which
consent shall not be unreasonably withheld. No Indemnifying Party shall, without
the prior written consent of the Indemnified Party, effect any settlement of any
pending Proceeding as to such Indemnified Party, unless such settlement includes
an unconditional release of such Indemnified Party from all liability on claims
that are the subject matter of such Proceeding.

                  All fees and expenses of the Indemnified Party (including
reasonable fees and expenses to the extent incurred in connection with
investigating or preparing to defend such Proceeding in a manner not
inconsistent with this Section) shall be paid to the Indemnified Party, as
incurred, within ten Trading Days of written notice thereof to the Indemnifying
Party (regardless of whether it is ultimately determined that an Indemnified
Party is not entitled to indemnification hereunder; provided, that the
Indemnifying Party may require such Indemnified Party to undertake to reimburse
all such fees and expenses to the extent it is finally judicially determined
that such Indemnified Party is not entitled to indemnification hereunder).

                  (d)      Contribution. If a claim for indemnification under
Section 5(a) or 5(b) is unavailable to an Indemnified Party (by reason of public
policy or otherwise), then each Indemnifying Party, in lieu of indemnifying such
Indemnified Party, shall contribute to the

                                                   Registration Rights Agreement

                                      -8-

<PAGE>

amount paid or payable by such Indemnified Party as a result of such Losses, in
such proportion as is appropriate to reflect the relative fault of the
Indemnifying Party and Indemnified Party in connection with the actions,
statements or omissions that resulted in such Losses as well as any other
relevant equitable considerations. The relative fault of such Indemnifying Party
and Indemnified Party shall be determined by reference to, among other things,
whether any action in question, including any untrue or alleged untrue statement
of a material fact or omission or alleged omission of a material fact, has been
taken or made by, or relates to information supplied by, such Indemnifying Party
or Indemnified Party, and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such action, statement or
omission. The amount paid or payable by a party as a result of any Losses shall
be deemed to include, subject to the limitations set forth in Section 5(c), any
reasonable attorneys' or other reasonable fees or expenses incurred by such
party in connection with any Proceeding to the extent such party would have been
indemnified for such fees or expenses if the indemnification provided for in
this Section was available to such party in accordance with its terms.

                  The parties hereto agree that it would not be just and
equitable if contribution pursuant to this Section 5(d) were determined by pro
rata allocation or by any other method of allocation that does not take into
account the equitable considerations referred to in the immediately preceding
paragraph. Notwithstanding the provisions of this Section 5(d), no Holder shall
be required to contribute, in the aggregate, any amount in excess of the amount
by which the proceeds actually received by such Holder from the sale of the
Registrable Securities subject to the Proceeding exceeds the amount of any
damages that such Holder has otherwise been required to pay by reason of such
untrue or alleged untrue statement or omission or alleged omission.

                  The indemnity and contribution agreements contained in this
Section are in addition to any liability that the Indemnifying Parties may have
to the Indemnified Parties.

         6.       Miscellaneous

                  (a)      Remedies. In the event of a breach by the Company or
by a Holder, of any of their obligations under this Agreement, each Holder or
the Company, as the case may be, in addition to being entitled to exercise all
rights granted by law and under this Agreement, including recovery of damages,
will be entitled to specific performance of its rights under this Agreement. The
Company and each Holder agree that monetary damages would not provide adequate
compensation for any losses incurred by reason of a breach by it of any of the
provisions of this Agreement and hereby further agrees that, in the event of any
action for specific performance in respect of such breach, it shall waive the
defense that a remedy at law would be adequate.

                  (b)      No Piggyback on Registrations. Except as and to the
extent specified in Schedule 6(b) hereto, neither the Company nor any of its
security holders (other than the Holders in such capacity pursuant hereto) may
include securities of the Company in the Registration Statement other than the
Registrable Securities, and the Company shall not after the date hereof enter
into any agreement providing any such right to any of its security holders.
Except as and to the extent specified in Schedule 6(b) hereto, the Company has
not previously entered into any

                                                   Registration Rights Agreement

                                      -9-

<PAGE>

agreement granting any registration rights with respect to any of its securities
to any Person which have not been fully satisfied.

                  (c)      Compliance. Each Holder covenants and agrees that it
will comply with the prospectus delivery requirements of the Securities Act as
applicable to it in connection with sales of Registrable Securities pursuant to
the Registration Statement.

                  (d)      Discontinued Disposition. Each Holder agrees by its
acquisition of such Registrable Securities that, upon receipt of a notice from
the Company of the occurrence of any event of the kind described in Section
3(c)(iii), (iv) and (v), such Holder will forthwith discontinue disposition of
such Registrable Securities under the Registration Statement until such Holder's
receipt of the copies of the supplemented Prospectus and/or amended Registration
Statement or until it is advised in writing (the "ADVICE") by the Company that
the use of the applicable Prospectus may be resumed, and, in either case, has
received copies of any additional or supplemental filings that are incorporated
or deemed to be incorporated by reference in such Prospectus or Registration
Statement. The Company may provide appropriate stop orders to enforce the
provisions of this paragraph.

                  (e)      Piggy-Back Registrations. If at any time during the
Effectiveness Period there is not an effective Registration Statement covering
all of the Registrable Securities and the Company shall determine to prepare and
file with the Commission a registration statement relating to an offering for
its own account (to the extent permitted under the agreement pursuant to which
such registration rights are granted) or the account of others under the
Securities Act of any of its equity securities, other than on Form S-4 or Form
S-8 (each as promulgated under the Securities Act) or their then equivalents
relating to equity securities to be issued solely in connection with any
acquisition of any entity or business or equity securities issuable in
connection with stock option or other employee benefit plans, then the Company
shall send to each Holder written notice of such determination and, if within
fifteen days after receipt of such notice, any such Holder shall so request in
writing, the Company shall include in such registration statement all or any
part of such Registrable Securities such holder requests to be registered,
subject to customary underwriter cutbacks applicable to all holders of
registration rights.

                  (f)      Amendments and Waivers. The provisions of this
Agreement, including the provisions of this sentence, may not be amended,
modified or supplemented, and waivers or consents to departures from the
provisions hereof may not be given, unless the same shall be in writing and
signed by the Company and the Holders of all of the then outstanding Registrable
Securities. Notwithstanding the foregoing, a waiver or consent to depart from
the provisions hereof with respect to a matter that relates exclusively to the
rights of certain Holders and that does not directly or indirectly affect the
rights of other Holders may be given by Holders of at least a majority of the
Registrable Securities to which such waiver or consent relates, provided, that
the provisions of this sentence may not be amended, modified, or supplemented
except in accordance with the provisions of the immediately preceding sentence.

                  (g)      Notices. Any and all notices or other communications
or deliveries required or permitted to be provided hereunder shall be in writing
and shall be deemed given and effective on the earliest of (i) the date of
transmission, if such notice or communication is

                                                   Registration Rights Agreement

                                      -10-

<PAGE>

delivered via facsimile at the facsimile telephone number specified in this
Section prior to 6:30 p.m. (New York City time) on a Trading Day, (ii) the
Trading Day after the date of transmission, if such notice or communication is
delivered via facsimile at the facsimile telephone number specified in this
Agreement later than 6:30 p.m. (New York City time) on any date and earlier than
11:59 p.m. (New York City time) on such date, (iii) the Trading Day following
the date of mailing, if sent by nationally recognized overnight courier service,
or (iv) upon actual receipt by the party to whom such notice is required to be
given. The address for such notices and communications shall be as follows:

         If to the Company:      Zix Corporation
                                 2711 North Haskell Avenue
                                 Suite 2300 LB36
                                 Dallas, TX 75204
                                 Attn:  Chief Financial Officer
                                 Facsimile No.:  (214) 515-7390

         With a copy to:         Weil, Gotshal & Manges LLP
                                 200 Crescent Court, Suite 300
                                 Dallas, Texas  75201
                                 Attn:  R. Scott Cohen, Esq.
                                 Facsimile No.: (214) 746-7777

         If to a Purchaser:      To the address set forth under such
                                 Purchaser's name on the signature pages hereto.

         With a copy to:         Bryan Cave LLP
                                 1290 Avenue of the Americas
                                 New York, NY 10101
                                 Attn.: Eric L. Cohen, Esq.
                                 Fax No.: (212) 541-4630 and (212) 541-1432

         If to any other Person who is then the registered Holder:

                                 To the address of such Holder as it appears in
                                 the stock transfer books of the Company

or such other address as may be designated in writing hereafter, in the same
manner, by such Person.

                  (h)      Successors and Assigns. This Agreement shall inure to
the benefit of and be binding upon the successors and permitted assigns of each
of the parties and shall inure to the benefit of each Holder. The Company may
not assign its rights or obligations hereunder without the prior written consent
of each Holder. Each Holder may assign their respective rights hereunder in the
manner and to the Persons as permitted under the Purchase Agreement.

                                                   Registration Rights Agreement

                                      -11-

<PAGE>

                  (i)      Execution and Counterparts. This Agreement may be
executed in any number of counterparts, each of which when so executed shall be
deemed to be an original and, all of which taken together shall constitute one
and the same Agreement. In the event that any signature is delivered by
facsimile transmission, such signature shall create a valid binding obligation
of the party executing (or on whose behalf such signature is executed) the same
with the same force and effect as if such facsimile signature were the original
thereof.

                  (j)      Governing Law. All questions concerning the
construction, validity, enforcement and interpretation of this Agreement shall
be governed by and construed and enforced in accordance with the internal laws
of the State of New York, without regard to the principles of conflicts of law
thereof. Each party agrees that all Proceedings concerning the interpretations,
enforcement and defense of the transactions contemplated by this Agreement
(whether brought against a party hereto or its respective Affiliates, employees
or agents) shall be commenced exclusively in the state and federal courts
sitting in the City of New York, Borough of Manhattan (the "NEW YORK COURTS").
Each party hereto hereby irrevocably submits to the exclusive jurisdiction of
the New York Courts 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
Proceeding, any claim that it is not personally subject to the jurisdiction of
any New York Court, or that such Proceeding has been commenced in an improper or
inconvenient forum. Each party hereto hereby irrevocably waives personal service
of process and consents to process being served in any such Proceeding by
mailing a copy thereof via registered or certified mail or overnight delivery
(with evidence of delivery) to such party at the address in effect for 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. Each party hereto hereby irrevocably waives, to the fullest
extent permitted by applicable law, any and all right to trial by jury in any
legal proceeding arising out of or relating to this Agreement or the
transactions contemplated hereby. If either party shall commence a Proceeding to
enforce any provisions of this Agreement, then the prevailing party in such
Proceeding shall be reimbursed by the other party for its attorney's fees and
other costs and expenses incurred with the investigation, preparation and
prosecution of such Proceeding.

                  (k)      Cumulative Remedies. The remedies provided herein are
cumulative and not exclusive of any remedies provided by law.

                  (l)      Severability. If any term, provision, covenant or
restriction of this Agreement is held by a court of competent jurisdiction to be
invalid, illegal, void or unenforceable, the remainder of the terms, provisions,
covenants and restrictions set forth herein shall remain in full force and
effect and shall in no way be affected, impaired or invalidated, and the parties
hereto shall use their reasonable efforts to find and employ an alternative
means to achieve the same or substantially the same result as that contemplated
by such term, provision, covenant or restriction. It is hereby stipulated and
declared to be the intention of the parties that they would have executed the
remaining terms, provisions, covenants and restrictions without including any of
such that may be hereafter declared invalid, illegal, void or unenforceable.

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

                                                   Registration Rights Agreement

                                      -12-

<PAGE>

                  (n)      Independent Nature of Purchasers' Obligations and
Rights. The obligations of each Purchaser hereunder is several and not joint
with the obligations of any other Purchaser hereunder, and no Purchaser shall be
responsible in any way for the performance of the obligations of any other
Purchaser hereunder. Nothing contained herein or in any other agreement or
document delivered at any closing, and no action taken by any Purchaser pursuant
hereto or thereto, shall be deemed to constitute the Purchasers as a
partnership, an association, a joint venture or any other kind of entity, or
create a presumption that the Purchasers are in any way acting in concert with
respect to such obligations or the transactions contemplated by this Agreement.
Each Purchaser shall be entitled to protect and enforce its rights, including
without limitation the rights arising out of this Agreement, and it shall not be
necessary for any other Purchaser to be joined as an additional party in any
proceeding for such purpose.

                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                           SIGNATURE PAGES TO FOLLOW]

                                                   Registration Rights Agreement

                                      -13-

<PAGE>

                  IN WITNESS WHEREOF, the parties have executed this
Registration Rights Agreement as of the date first written above.

                                    Zix Corporation

                                    By:    /s/ Ronald A. Woessner
                                           ----------------------------------
                                    Name:  Ronald A. Woessner
                                    Title: Senior Vice President

                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                     SIGNATURE PAGES OF PURCHASER TO FOLLOW]

                                                   Registration Rights Agreement

<PAGE>

                  IN WITNESS WHEREOF, the parties have executed this
Registration Rights Agreement as of the date first written above.

                                    Gryphon Master Fund, LP


                                    By: /s/ E.B. Lyon IV
                                        ----------------------------------------
                                        Name:  E.B. Lyon IV
                                        Title: Authorized Agent

                                    Address for Notice:  500 Crescent Court #270
                                                         Dallas, TX 75201
                                    Facsimile No.:       Tel: 214-871-6900
                                    Attn:                Fax: 214-871-6909

                                    DEEPHAVEN SMALL CAP GROWTH FUND, LLC

                                    By: /s/ Jim Korn
                                        ----------------------------------------
                                        Name:  Jim Korn
                                        Title: Chief Legal Counsel

                                    Address for Notice:  130 Cheshire Lane
                                                         Minnetonka, MN 55305

                                    Facsimile No.:       (952) 249-5320
                                    Attn:                Bruce Lieberman

                                    Vertical Ventures Investments, LLC

                                    By: /s/ Joshua Silverman
                                        ----------------------------------------
                                        Name:  Joshua Silverman
                                        Title: Manager

                                    Address for Notice:  641 Lexington Avenue,
                                                         26th Floor
                                                         New York, NY 10022
                                    Facsimile No.:       212-207-3454
                                    Attn:                Joshua Silverman

                                    Bonanza Master Fund Ltd.

                                    By: /s/ Brian Ladin
                                        ----------------------------------------
                                        Name:  Brian Ladin
                                        Title: Managing Director

                                    Address for Notice:  8235 Douglas, Suite 423
                                                         Dallas, TX 75225
                                    Facsimile No.:       214.853.5013
                                    Attn:                Brian Ladin

<PAGE>

                                    LANGLEY PARTNERS, L.P.

                                    By: /s/ Jeffrey Thorp
                                        ----------------------------------------
                                      Name:  JEFFREY THORP
                                      Title: MANAGING PARTNER OF G.P.

                                    Address:      c/o Langley Capital, LLC 535
                                                  Madison Avenue, 7th Floor
                                                  New York, NY 10022
                                                  (212) 850-7528 Telephone
                                                  (212) 850-7589 Facsimile
                                                  jt@lcap.com

                                    Investment Amount:        $500,000

                                    ALPHA CAPITAL A.G.

                                    By: /s/  Konrad Ackermann
                                        ----------------------------------------
                                        Name:  Konrad Ackermann
                                        Title: Director


                                    Address for Notice:

                                    Pradafant 7, Furstentums 9490
                                    Vaduz Liechtenstein
                                    Facsimile No.:
                                    Attn:

                                    SUPERIUS SECURITIES GROUP, INC
                                    MONEY PURCHASE PLAN

                                    By: /s/  James Hudgins
                                        ----------------------------------------
                                        Name:  James Hudgins
                                        Title: Trustee


                                    Address for Notice:

                                    94 Grand Avenue
                                    Englewood,  NJ 07631
                                    Facsimile No.: (201) 568-9392
                                    Attn: James Hudgins

<PAGE>

                                                                         Annex A

                              Plan of Distribution

         The Selling Stockholders and any of their pledgees, assignees and
successors-in-interest may, from time to time, sell any or all of their shares
of Common Stock on any stock exchange, market or trading facility on which the
shares are traded or in private transactions. These sales may be at fixed or
negotiated prices. The Selling Stockholders may use any one or more of the
following methods when selling shares:

-        ordinary brokerage transactions and transactions in which the
         broker-dealer solicits purchasers;

-        block trades in which the broker-dealer will attempt to sell the shares
         as agent but may position and resell a portion of the block as
         principal to facilitate the transaction;

-        purchases by a broker-dealer as principal and resale by the
         broker-dealer for its account;

-        an exchange distribution in accordance with the rules of the applicable
         exchange;

-        privately negotiated transactions;

-        short sales

-        broker-dealers may agree with the Selling Stockholders to sell a
         specified number of such shares at a stipulated price per share;

-        a combination of any such methods of sale; and

-        any other method permitted pursuant to applicable law.

         The Selling Stockholders may also sell shares under Rule 144 under the
Securities Act, if available, rather than under this prospectus.

         Broker-dealers engaged by the Selling Stockholders may arrange for
other brokers-dealers to participate in sales. Broker-dealers may receive
commissions or discounts from the Selling Stockholders (or, if any broker-dealer
acts as agent for the purchaser of shares, from the purchaser) in amounts to be
negotiated. The Selling Stockholders do not expect these commissions and
discounts to exceed what is customary in the types of transactions involved.

         The Selling Stockholders may from time to time pledge or grant a
security interest in some or all of the Shares or Warrant Shares owned by them
and, if they default in the performance of their secured obligations, the
pledgees or secured parties may offer and sell shares of Common Stock from time
to time under this prospectus, or under an amendment to this prospectus under
Rule 424(b)(3) or other applicable provision of the Securities Act of 1933

                                                   Registration Rights Agreement

<PAGE>

amending the list of selling stockholders to include the pledgee, transferee or
other successors in interest as selling stockholders under this prospectus.

         The Selling Stockholders also may transfer the shares of common stock
in other circumstances, in which case the transferees, pledgees or other
successors in interest will be the selling beneficial owners for purposes of
this prospectus.

         The Selling Stockholders and any broker-dealers or agents that are
involved in selling the shares may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales. In such event, any
commissions received by such broker-dealers or agents and any profit on the
resale of the shares purchased by them may be deemed to be underwriting
commissions or discounts under the Securities Act. The Selling Stockholders have
informed the Company that it does not have any agreement or understanding,
directly or indirectly, with any person to distribute the Common Stock.

         The Company is required to pay all fees and expenses incident to the
registration of the shares. The Company has agreed to indemnify the Selling
Stockholders against certain losses, claims, damages and liabilities, including
liabilities under the Securities Act.

                                                   Registration Rights Agreement

<PAGE>

                                  SCHEDULE 6(b)
                                       TO
                          REGISTRATION RIGHTS AGREEMENT

In September 2002, in exchange for $2,000,000 in cash, the Company issued to
Antonio R. Sanchez, Jr., a former director and approximate 12.6% shareholder of
the Company, and related entities, 504,545 shares of its Series A Convertible
Preferred Stock and warrants to purchase 177,381 shares of its Common Stock. In
connection therewith, Mr. Sanchez received (i) certain registration rights
whereby he can demand the registration of up to 666,667 of previously owned
shares and (ii) piggyback rights if the Company fails to maintain effectiveness
of any registration statement required to be filed pursuant to the foregoing
registration rights.

In September 2002, in exchange for $3,450,000 in cash, the Company issued to
George W. Haywood, a private investor and approximate 25.4% shareholder of the
Company, 947,708 shares of its Series B Convertible Preferred Stock and warrants
to purchase 304,986 shares of its Common Stock. In connection therewith, Mr.
Haywood received (i) certain registration rights whereby he can demand the
registration of up to 1,333,333 of previously owned shares and (ii) piggyback
rights if the Company fails to maintain effectiveness of any registration
statement required to be filed pursuant to the foregoing registration rights.

In August 1999, the Company issued to CStone Consulting, Inc. options to acquire
50,000 shares of the Company's Common Stock. In connection therewith, CStone
received certain registration rights whereby it can demand the registration of
the 50,000 vested shares.

The Company has issued to Henry Kuehne options to acquire 50,000 shares of the
Company's Common Stock. In connection therewith, the first 25,000 vested shares
have been registered with the Securities and Exchange Commission. Mr. Kuehne
received certain registration rights whereby he can demand the registration of
the remaining 25,000 vested shares.