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                                                                     EXHIBIT 4.3

                                                                  EXECUTION COPY

                          REGISTRATION RIGHTS AGREEMENT

         REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT"), dated as of September
2, 2003, by and between Zix Corporation, a Texas corporation, with its
headquarters located at 2711 North Haskell Avenue, Suite 2300 LB36, Dallas,
Texas 75204 (the "COMPANY"), and Elron Software, Inc., a Delaware corporation
("SELLER").

         WHEREAS:

         A.       In connection with an Asset Purchase Agreement between the
Company, Seller, Seller's parent corporation, Elron Electronic Industries Ltd.,
an Israeli corporation (the "PARENT") and Seller's subsidiary, Elron Software
(2000) Ltd., an Israeli corporation, dated of even date herewith (the "ASSET
PURCHASE AGREEMENT"), the Company has agreed, upon the terms and subject to the
conditions contained therein, to issue and sell to Seller (Seller and other
persons and entities made parties to this Agreement pursuant to Section 10.7, if
any, are referred to herein as the "SELLING SHAREHOLDERS") the shares of its
Common Stock, par value $.01 per share (the "COMMON STOCK"), and to issue to
Seller a Convertible Promissory Note, which is convertible into Common Stock, in
each case as referenced in Section 4.1 of the Asset Purchase Agreement; and

         B.       To induce Seller and Parent to execute and deliver the Asset
Purchase 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 the
Selling Shareholders hereby agree as follows:

                                     ARTICLE I.
                                    DEFINITIONS

         Section 1.1. As used in this Agreement, the following terms shall have
the following meanings:

                  (a)      "REGISTER," "REGISTERED," and "REGISTRATION" refer to
         a registration effected by preparing and filing a Registration
         Statement or Statements 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 basis ("RULE 415"), and the
         declaration or ordering of effectiveness of such Registration Statement
         by the United States Securities and Exchange Commission (the "SEC").

                  (b)      "REGISTRABLE SECURITIES" means (i) shares of Common
         Stock issued pursuant to the Asset Purchase Agreement held by a Selling
         Shareholder, (ii) the shares

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         of Common Stock issuable upon conversion of the Convertible Promissory
         Note held by Seller and (iii) any shares of Common Stock issued as a
         dividend or other distribution with respect to, or in exchange for or
         in replacement of, all such shares of Common Stock described in clauses
         (i) and (ii).

                  (c)      "REGISTRATION STATEMENT" means a registration
         statement of the Company under the 1933 Act.

         Section 1.2. Capitalized terms used herein and not otherwise defined
herein shall have the respective meanings set forth in the Asset Purchase
Agreement.

                                   ARTICLE II.
                                  REGISTRATION

         Section 2.1. REGISTRATION. The Company shall prepare, and file with the
SEC within the later of (i) 30 days of the Closing Date and (ii) the date which
the registration statement filed by the Company pursuant that certain
Registration Rights Agreement, dated as of July 22, 2003, by and between the
Company and PocketScript L.L.C. has been declared effective by the SEC (such
date, the "FILING DATE") a Registration Statement on Form S-3 (or, if Form S-3
is not then available, on such form of Registration Statement as is then
available to effect a registration of the Registrable Securities, subject to the
consent of the Selling Shareholders holding a majority of the Registrable
Securities, which consent will not be unreasonably withheld, conditioned or
delayed) covering the resale of the Registrable Securities. The Company shall
provide a draft of the Registration Statement to a single counsel for the
Selling Shareholders prior to its filing or other submission so that such
counsel has a reasonable opportunity to review and comment on the Registration
Statement prior to it being filed. The Company shall use all commercially
reasonable efforts to obtain effectiveness of the Registration Statement as soon
as possible thereafter. If (i) the Registration Statement is not filed by the
Filing Date, (ii) the Registration Statement is not declared effective by the
SEC by the close of business on the 100th day following the Closing Date or
(iii) once declared effective by the SEC, sales of the Registrable Securities
cannot be made (other than during an Allowed Delay, as defined below) pursuant
to the Registration Statement due to the result of any action or inaction on the
part of the Company consistent with its obligations under this Agreement and
through no fault of the Selling Shareholders, then the Company shall pay to each
Selling Shareholder an amount equal to (i) U.S.$1,166.67 times (ii) (A) the
total number of Registrable Securities held by such holder divided by (B) the
total number of Registrable Securities, for each day the Registration Statement
is not filed, effective or available for sale, as applicable, payable on the
last business day of each month. The foregoing payment shall not be exclusive of
any other remedy at law or equity available to the Selling Shareholders for
failure of the Company to comply with its obligations under this Section 2.1;
provided that any damages recovered by the Selling Shareholders from the Company
in pursuing such remedies shall be offset by such payment.

         Section 2.2. UNDERWRITTEN OFFERING. If any offering pursuant to a
Registration Statement pursuant to Section 2.1 hereof involves an underwritten
offering, the Selling Shareholders shall have the right to select one legal
counsel and the right to select the investment banker or bankers and manager or
managers to administer the offering (subject to the approval of the Company,
which approval shall not be unreasonably withheld, conditioned or delayed). In

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the event that the Selling Shareholders elect not to participate in such
underwritten offering, the Registration Statement covering all of the
Registrable Securities shall contain appropriate plans of distribution
reasonably satisfactory to the Selling Shareholders holding a majority of the
Registrable Securities.

         Section 2.3. ELIGIBILITY FOR FORM S-3. The Company represents and
warrants that it meets the registrant eligibility and transaction requirements
for the use of Form S-3 for registration of the sale by the Selling Shareholders
and the Company shall file all reports required to be filed by the Company with
the SEC in a timely manner so as to maintain such eligibility for the use of
Form S-3.

                                  ARTICLE III.
                           OBLIGATIONS OF THE COMPANY

         In connection with the registration of the Registrable Securities, the
Company shall have the following obligations:

         Section 3.1. The Company shall prepare promptly, and file with the SEC
as soon as practicable after the Closing Date (but in no event later than the
Filing Date), a Registration Statement with respect to the Registrable
Securities, and thereafter use its commercially reasonable efforts to cause such
Registration Statement relating to Registrable Securities to become effective as
soon as possible after such filing. The Company shall use its commercially
reasonable efforts to keep the Registration Statement effective pursuant to Rule
415 at all times until such date as is the earlier of (i) the date on which all
of the Registrable Securities shall have been registered under the 1933 Act and
been sold or (ii) the date on which the Registrable Securities shall be (in the
opinion of counsel delivered to the Company), saleable immediately to the public
without registration or restriction (including, without limitation, as to volume
by each holder thereof) under the 1933 Act (the "EFFECTIVE PERIOD"), which
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 not misleading.

         Section 3.2. The Company shall prepare and file with the SEC such
amendments (including post-effective amendments) and supplements to the
Registration Statement and the prospectus used in connection with the
Registration Statement as may be necessary to keep the Registration Statement
effective at all times during the Effective 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 the Registration Statement,
including any amendments that may be required to allow the Selling Shareholders
to sell Registrable Securities under the Registration Statement.

         Section 3.3. The Company shall furnish to each Selling Shareholder
whose Registrable Securities are included in a Registration Statement and its
legal counsel (i) promptly after the same is prepared and publicly distributed,
filed with the SEC, or received by the Company, one copy of such Registration
Statement and any amendment thereto, each preliminary prospectus and prospectus
and each amendment or supplement thereto, and (ii) such number of copies of a
prospectus, including a preliminary prospectus, and all amendments and
supplements thereto and

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such other documents as such Selling Shareholder may reasonably request in order
to facilitate the disposition of the Registrable Securities owned by such
Selling Shareholder. The Company will immediately notify each Selling
Shareholder of the effectiveness of such Registration Statement or any
post-effective amendment. The Company will promptly respond to any and all
comments received from the SEC, with a view towards causing such Registration
Statement or any amendment thereto to be declared effective by the SEC as soon
as practicable and shall file an acceleration request as soon as practicable
following the resolution or clearance of all SEC comments or, if applicable,
following notification by the SEC that such Registration Statement or any
amendment thereto will not be subject to review.

         Section 3.4. The Company shall use reasonable efforts to (i) register
and qualify the Registrable Securities covered by the Registration Statement
under such other securities or "BLUE SKY" laws of such jurisdictions in the
United States as each Selling Shareholder may reasonably request, if an
exemption from such securities or blue sky laws is not otherwise available, (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 Effective Period, (iii) take such other actions as may be necessary to
maintain such registrations and qualifications in effect at all times during the
Effective 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 (a) qualify to do business in any
jurisdiction where it would not otherwise be required to qualify but for this
Section 3.4, (b) subject itself to general taxation in any such jurisdiction,
(c) file a general consent to service of process in any such jurisdiction, or
(d) make any change in its charter or bylaws, which in each case the Board of
Directors of the Company determines to be contrary to the best interests of the
Company and its shareholders.

         Section 3.5. In the event the Selling Shareholders select underwriters
for the offering, the Company shall enter into and perform its obligations under
an underwriting agreement, in usual and customary form, including, without
limitation, customary indemnification and contribution obligations, with the
underwriters of such offering.

         Section 3.6. As promptly as practicable after becoming aware of such
event, the Company shall notify each Selling Shareholder of the happening of any
event, of which the Company has knowledge, 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 not misleading, and
use its commercially reasonable efforts promptly to prepare a supplement or
amendment to a Registration Statement to correct such untrue statement or
omission, and deliver such number of copies of such supplement or amendment to
each Selling Shareholder as such Selling Shareholder may reasonably request;
provided that, for not more than fifteen (15) consecutive trading days (or a
total of not more than thirty (30) trading days in any twelve (12) month
period), the Company may delay the disclosure of material non-public information
concerning the Company (as well as prospectus or Registration Statement
updating) the disclosure of which at the time is not, in the good faith opinion
of the Company, in the best interests of the Company (an "ALLOWED DELAY");
provided, further, that the Company shall promptly (i) notify the Selling
Shareholders in writing of the existence of (but in no event,

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without the prior written consent of a Selling Shareholder, shall the Company
disclose to such Selling Shareholder any of the facts or circumstances
regarding) material non-public information giving rise to an Allowed Delay and
(ii) advise the Selling Shareholders in writing to cease all sales under such
Registration Statement until the end of the Allowed Delay. Upon expiration of
the Allowed Delay, the Company shall again be bound by the first sentence of
this Section 3.6 with respect to the information giving rise thereto.

         Section 3.7. The Company shall use its commercially reasonable efforts
to prevent the issuance of any stop order or other suspension of effectiveness
of any Registration Statement, and, if such an order is issued, to obtain the
withdrawal of such order at the earliest possible moment and to notify each
Selling Shareholder who holds Registrable Securities being sold (or, in the
event of an underwritten offering, the managing underwriters) of the issuance of
such order and the resolution thereof.

         Section 3.8. The Company shall permit a single firm of counsel
designated by the Selling Shareholders holding a majority of the Registrable
Securities to review the Registration Statement, and all amendments and
supplements thereto (as well as all requests for acceleration or effectiveness
thereof (collectively, the "REGISTRATION DOCUMENTS")) a reasonable period of
time prior to their filing with the SEC, and not file (or send) any Registration
Documents in a form to which such counsel reasonably objects and will not
request acceleration of such Registration Statement without prior notice to such
counsel. The sections of such Registration Statement covering information with
respect to the Selling Shareholders, the Selling Shareholders' beneficial
ownership of securities of the Company or the Selling Shareholders's intended
method of disposition of Registrable Securities shall conform to the information
provided to the Company by the Selling Shareholders.

         Section 3.9. The Company shall (i) cause all the Registrable Securities
covered by the Registration Statement to be listed on each national 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) to the extent the securities
of the same class or series are not then listed or permitted to be listed on a
national securities exchange, secure the designation and quotation of all the
Registrable Securities covered by the Registration Statement on the Nasdaq
National Market or, if not eligible for Nasdaq on the Nasdaq SmallCap Market.

         Section 3.10. The Company shall provide a transfer agent and registrar,
which may be a single entity, for the Registrable Securities not later than the
effective date of the Registration Statement.

         Section 3.11. At the request of the Selling Shareholders, the Company
shall prepare and file with the SEC such amendments (including post-effective
amendments) and supplements to a Registration Statement and any prospectus used
in connection with the Registration Statement as may be necessary in order to
change the plan of distribution set forth in such Registration Statement.

         Section 3.12. The Company shall not, and shall not agree to, allow the
holders of any securities of the Company to include any of their securities in
any Registration Statement under

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Section 2.1 hereof or any amendment or supplement thereto under Section 3.2
hereof without the consent of the Selling Shareholders holding a majority of the
Registrable Securities. In addition, the Company shall not offer any securities
for its own account or the account of others in any Registration Statement under
Section 2.1 hereof or any amendment or supplement thereto under Section 3.2
hereof without the consent of the Selling Shareholders.

         Section 3.13. The Company shall take all other reasonable actions
necessary to expedite and facilitate disposition by the Selling Shareholders of
Registrable Securities pursuant to a Registration Statement.

         Section 3.14. The Company shall comply with all applicable laws related
to a Registration Statement and offering and sale of securities and all
applicable rules and regulations of governmental authorities in connection
therewith (including without limitation the 1933 Act and the 1934 Act (as
defined below) and the rules and regulations promulgated by the SEC).

                                  ARTICLE IV.
                     OBLIGATIONS OF THE SELLING SHAREHOLDERS

         In connection with the registration of the Registrable Securities, the
Selling Shareholders shall have the following obligations:

         Section 4.1. 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 Selling Shareholder that such
Selling Shareholder shall furnish to the Company 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. At least ten (10) days prior to the first anticipated filing
date of the Registration Statement, the Company shall notify each Selling
Shareholder of the information the Company requires from each such Selling
Shareholder.

         Section 4.2. Each Selling Shareholder, by such Selling Shareholder'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 the Registration Statement hereunder, unless such Selling Shareholder
has notified the Company in writing of such Selling Shareholder's election to
exclude all of such Selling Shareholder's Registrable Securities from the
Registration Statement.

         Section 4.3. If the services of an underwriter are engaged, each
Selling Shareholder agrees to enter into and perform such Selling Shareholder's
obligations under an underwriting agreement, in usual and customary form,
including, without limitation, customary indemnification and contribution
obligations, with the managing underwriter of such offering and take such other
actions as are reasonably required in order to expedite or facilitate the
disposition of the Registrable Securities, unless such Selling Shareholder has
notified the Company in writing of such Selling Shareholder's election to
exclude all of such Selling Shareholder's Registrable Securities from such
Registration Statement.

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         Section 4.4. Each Selling Shareholder agrees that, upon receipt of any
notice from the Company of the happening of any event of the kind described in
Section 3.6 or 3.7, such Selling Shareholder will immediately discontinue
disposition of Registrable Securities pursuant to the Registration Statement
covering such Registrable Securities until such Selling Shareholder's receipt of
the copies of the supplemented or amended prospectus contemplated by Section 3.6
or 3.7 and, if so directed by the Company, such Selling Shareholder shall
deliver to the Company or destroy all copies in such Selling Shareholder's
possession, of the prospectus covering such Registrable Securities current at
the time of receipt of such notice.

         Section 4.5. No Selling Shareholder may participate in any underwritten
registration hereunder unless such Selling Shareholder (i) agrees to sell such
Selling Shareholder's Registrable Securities on the basis provided in any
underwriting arrangements in usual and customary form entered into by the
Company, (ii) completes and executes all questionnaires, powers of attorney,
indemnities, underwriting agreements and other documents reasonably required
under the terms of such underwriting arrangements, and (iii) agrees to pay its
pro rata share of all underwriting discounts and commissions and any expenses in
excess of those payable by the Company pursuant to Section 5 below.

         Section 4.6. The Selling Shareholder shall comply with all applicable
laws related to a Registration Statement and offering and sale of securities and
all applicable rules and regulations of governmental authorities in connection
therewith (including without limitation the 1933 Act and the 1934 Act (as
defined below) and the rules and regulations promulgated by the SEC).

                                   ARTICLE V.
                            EXPENSES OF REGISTRATION

         All reasonable expenses, other than underwriting discounts and
commissions, incurred in connection with registrations, filings or
qualifications pursuant to Sections 2 and 3, including, without limitation, all
registration, listing and qualification fees, printers and accounting fees, the
fees and disbursements of legal counsel for the Company, and the reasonable fees
and disbursements of one legal counsel for all holders of Registrable
Securities, selected by the Selling Shareholders pursuant to Sections 2.2 and
3.8 hereof, shall be borne by the Company.

                                   ARTICLE VI.
                                 INDEMNIFICATION

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

         Section 6.1. The Company will indemnify, hold harmless and defend (i)
each Selling Shareholder who holds such Registrable Securities, (ii) the
directors, officers, partners, employees, agents and each person who controls
any Selling Shareholder within the meaning of the 1933 Act or the Securities
Exchange Act of 1934, as amended (the "1934 ACT"), if any, (iii) any underwriter
(as defined in the 1933 Act) for the Selling Shareholders, and (iv) the
directors, officers, partners, employees and each person who controls any such
underwriter within the meaning of the 1933 Act or the 1934 Act, if any (each, an
"INDEMNIFIED PERSON"), against any joint or several losses, claims, damages,
liabilities or expenses (collectively, together

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with actions, proceedings or inquiries by any regulatory or self-regulatory
organization, whether commenced or threatened, in respect thereof, "CLAIMS") to
which any of them may become subject insofar as such Claims arise out of or are
based upon: (i) any untrue statement or alleged untrue statement of a material
fact in a Registration Statement or the omission or alleged omission to state
therein a material fact required to be stated 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; or (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 (the matters in the foregoing clauses (i)
through (iii) being, collectively, "VIOLATIONS"). Subject to the restrictions
set forth in Section 6.3 with respect to the number of legal counsel, the
Company shall reimburse the Indemnified Person, promptly as such expenses are
incurred and are due and payable, for any reasonable 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 6.1: (i) shall
not apply to a Claim 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 any Indemnified Person or underwriter for such Indemnified Person
expressly for use in connection with the preparation of such Registration
Statement or any such amendment thereof or supplement thereto; (ii) 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; (iii) with respect to any preliminary prospectus, shall
not inure to the benefit of any Indemnified Person 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, such
corrected prospectus was timely made available by the Company pursuant to
Section 3.3 hereof, 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; and (iv)
shall not apply to any offers to sell or sales made by an Indemnified Person
after receipt of the notice referred to in Section 3.6, clause (ii) and during
the period of the Allowed Delay. 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
Selling Shareholders pursuant to Section 10.7.

         Section 6.2. In connection with any Registration Statement in which a
Selling Shareholder is participating, each such Selling Shareholder agrees
severally and not jointly to indemnify, hold harmless and defend, to the same
extent and in the same manner set forth in Section 6.1, the Company, each of its
directors, 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, any underwriter and any other shareholder selling securities
pursuant to the Registration Statement or any of its directors or officers or
any person who controls such shareholder or underwriter within the meaning of
the 1933 Act or the 1934 Act (collectively and together with an Indemnified
Person, an "INDEMNIFIED PARTY"), against any Claim to which any

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of them may become subject, under the 1933 Act, the 1934 Act or otherwise,
insofar as such Claim arises out of or is based upon (i) 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 Selling Shareholder expressly for use in connection with such
Registration Statement or (ii) any offers to sell or sales by such Selling
Shareholder after receipt by such Selling Shareholder of the notice referred to
in Section 3.6, clause (ii) and during the period of the Allowed Delay; and
subject to Section 6.3, such Selling Shareholder will reimburse any legal or
other expenses (promptly as such expenses are incurred and are due and payable)
reasonably incurred by them in connection with investigating or defending any
such Claim; provided, however, that the indemnity agreement contained in this
Section 6.2 shall not apply to amounts paid in settlement of any Claim if such
settlement is effected without the prior written consent of such Selling
Shareholder, which consent shall not be unreasonably withheld; provided,
further, however, that the Selling Shareholders shall be liable under this
Agreement (including this Section 6.2 and Section 7) for only that amount as
does not exceed the net proceeds to such Selling Shareholder 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 Selling Shareholders pursuant to Section 10.7.
Notwithstanding anything to the contrary contained herein, the indemnification
agreement contained in this Section 6.2 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, and the Indemnified Party was promptly advised in writing not to
use the incorrect information prior to the use giving rise to a Violation and
such Indemnified Party, notwithstanding such advice, used it.

         Section 6.3. Promptly after receipt by an Indemnified Party under this
Section 6 of notice of the commencement of any action (including any
governmental action), such 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 the defense thereof with counsel
selected by the indemnifying party and reasonably satisfactory to the
Indemnified Party, as the case may be; provided, however, that an Indemnified
Party shall have the right to retain its own counsel with the fees and expenses
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 Party and the indemnifying party would be inappropriate due to
actual or potential differing interests between such Indemnified Party and any
other party represented by such counsel in such proceeding. The indemnifying
party shall pay for only one separate legal counsel for the Indemnified Persons
or the Indemnified Parties, as applicable, and such legal counsel shall be
selected by the Selling Shareholders, if the Selling Shareholders are entitled
to indemnification hereunder, or the Company, if the Company is entitled to
indemnification hereunder, as applicable. 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 Party under this Section 6, except to the extent that the
indemnifying party is actually prejudiced in its ability to defend such action.
The indemnification required by this Section 6 shall be made

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by periodic payments of the amount thereof during the course of the
investigation or defense, as such expense, loss, damage or liability is incurred
and is due and payable.

                                  ARTICLE VII.
                                  CONTRIBUTION

         If the indemnification provided for in Article 6 above is held by a
court of competent jurisdiction to be unavailable to an Indemnified Party with
respect to any loss, liability, claim, damage or expense referred to herein,
then the indemnifying party, in lieu of indemnifying the Indemnified Party,
shall contribute to the amount paid or payable by such Indemnified Party with
respect to such loss, liability, claim, damage or expense in the proportion that
is appropriate to reflect the relative fault of the indemnifying party and the
Indemnified Party in connection with the statements or omissions that resulted
in such loss, liability, claim, damage or expense, as well as any other relevant
equitable considerations. The relative fault of the indemnifying party and the
Indemnified Party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of material fact or the omission
to state a material fact relates to information supplied by the indemnifying
party or by the Indemnified Party, and the parties' relative intent, knowledge,
access to information and opportunity to correct or prevent such statement or
omission. In any such case, (i) no contribution shall be made under
circumstances where the indemnifying party would not have been liable for
indemnification under the fault standards set forth in Section 6, (ii) no
Selling Shareholder guilty of fraudulent misrepresentation (within the meaning
of Section 11(f) of the 1933 Act) shall be entitled to contribution from any
Selling Shareholder who was not guilty of such fraudulent misrepresentation, and
(iii) contribution (together with any indemnification or other obligations under
this Agreement) by any Selling Shareholder shall be limited in amount to the net
amount of proceeds received by such Selling Shareholder from the sale of such
Registrable Securities.

                                 ARTICLE VIII.
                           REPORTS UNDER THE 1934 ACT

         With a view to making available to the Selling Shareholders 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 Selling Shareholders 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 and the
         filing of such reports and other documents is required for the
         applicable provisions of Rule 144; and

                  (c)      furnish to each Selling Shareholder so long as such
         Selling Shareholder owns Registrable Securities, promptly upon request,
         such information as may be reasonably requested to permit such Selling
         Shareholder to sell such securities pursuant to Rule 144 without
         registration.

                                       10

<PAGE>

                                  ARTICLE IX.
                        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 written consent of the Company and
the Selling Shareholders.

                                   ARTICLE X.
                                  MISCELLANEOUS

         Section 10.1. If at any time during the Effective 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 SEC a registration
statement relating to an offering for its own account or the account of other
shareholders of the Company under the 1933 Act of any of its equity securities,
other than on Form S-4 or Form S-8 (each as promulgated under the 1933 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, and
other than any registration statements filed in connection with the registration
of shares of Common Stock issued or issuable with respect to any antidilution
adjustments resulting from the issuance of the Registrable Securities, then the
Company shall send to each Selling Shareholder written notice of such
determination and, if within 15 days after receipt of such notice, any such
Selling Shareholder shall so request in writing, the Company shall (to the
extent permitted under, and consistent with the terms and conditions of, any
agreement pursuant to which such registration rights are granted or governed)
include in such registration statement all or any part of such Registrable
Securities such holder requests to be registered.

         Section 10.2. A person or entity is deemed to be a holder of
Registrable Securities whenever such person or entity owns of record such
Registrable Securities. If the Company receives conflicting instructions,
notices or elections from two or more persons or entities 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.

         Section 10.3. Any notices required or permitted to be given under the
terms hereof shall be given in the manner sent by certified or registered mail
(return receipt requested) or delivered personally or by courier (including a
recognized overnight delivery service) or by facsimile and shall be effective
five (5) calendar days after being placed in the mail, if mailed by regular
United States mail, or upon receipt, if delivered personally or by courier
(including a recognized overnight delivery service) or by facsimile, in each
case addressed to a party. The addresses and facsimile numbers for such
communications shall be:

                                       11

<PAGE>

                           If to the Company:

                           Zix Corporation
                           2711 North Haskell Avenue
                           Suite 2300 LB36
                           Dallas, Texas 75204
                           Attention: General Counsel
                           Facsimile: (214) 515-7385

If to a Selling Shareholder, to the address and facsimile number set forth in
the Asset Purchase Agreement with a copy to the counsel specified in the Asset
Purchase Agreement or (in the case of permitted assigns, below the Selling
Shareholder's signature on the joinder page to this Agreement).

         Section 10.4. 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.

         Section 10.5. THIS AGREEMENT WILL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REFERENCE TO THE
PRINCIPLES OF CONFLICT OF LAWS OR ANY OTHER PRINCIPLE THAT COULD RESULT IN THE
APPLICATION OF THE LAWS OF ANY OTHER JURISDICTION.

         Section 10.6. This Agreement and the Asset Purchase Agreement
(including all schedules and exhibits thereto) 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. This Agreement and the Asset
Purchase Agreement supersede all prior agreements and understandings among the
parties hereto with respect to the subject matter hereof and thereof.

         Section 10.7. Seller may assign its rights hereunder to (i) any
affiliate of Seller or (ii) to one or more parties acquiring at least 20% of
total Registrable Securities outstanding; provided that each such affiliate or
party shall be required to execute a joinder page indicating its agreement to be
bound to the terms and conditions of this Agreement. This Agreement shall inure
to the benefit of and be binding upon the successors and permitted assigns of
each of the parties hereto.

         Section 10.8. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

         Section 10.9. This Agreement may be executed in two or more
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.

                                       12

<PAGE>

         Section 10.10. 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.

         Section 10.11. 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.

         Section 10.12. In the event that any provision of this Agreement is
invalid or unenforceable under any applicable statute or rule of law, then such
provision shall be deemed inoperative to the extent that it may conflict
therewith and shall be deemed modified to conform with such statute or rule of
law. Any provision hereof which may prove invalid or unenforceable under any law
shall not affect the validity or enforceability of any other provision hereof.

                [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                       13

<PAGE>

         IN WITNESS WHEREOF, the Company and Seller have caused this Agreement
to be duly executed as of the date first above written.

                                    ZIX CORPORATION

                                    By: /s/ RONALD A. WOESSNER
                                        ----------------------------------------
                                        Name: Ronald A. Woessner
                                             -----------------------------------
                                        Title: S.V.P.
                                               ---------------------------------


                                    ELRON SOFTWARE, INC.

                                    By: /s/ ADAM N. BOSNIAN
                                        ----------------------------------------
                                        Name: Adam N. Bosnian
                                             -----------------------------------
                                        Title: Co-General Manager
                                              ----------------------------------


                                    By: /s/ HENRY R. TUMBLIN
                                        ----------------------------------------
                                        Name: Henry R. Tumblin
                                             -----------------------------------
                                        Title: Co-General Manager
                                               ---------------------------------
                                       14

<PAGE>

                                     JOINDER

         The undersigned, who represents that it is an Affiliate of Elron
Software, Inc. and has acquired 1,709,402 shares of Common Stock of Zix
Corporation from Elron Software, Inc., hereby executes this signature page to
that certain Registration Rights Agreement (the "Registration Rights
Agreement"), dated September 2, 2003, between Elron Software, Inc. and Zix
Corporation, thereby indicating the undersigned's agreement to the terms and
conditions of the Registration Rights Agreement, as fully and effectively as if
the undersigned had executed and delivered this page at the time originally
executed by each of Elron Software, Inc. and Zix Corporation.

                                    ELRON ELECTRONIC INDUSTRIES LTD.

                                    By: /s/ DORAN BIRGER
                                        ----------------------------------------
                                        Name: Doran Birger
                                              ----------------------------------
                                        Title: President & CEO
                                               ---------------------------------

                                    By: /s/ PAUL WEINBERG
                                        ----------------------------------------
                                        Name: Paul Weinberg
                                              ----------------------------------
                                        Title: General Counsel & Corp Secretary
                                               ---------------------------------

                                    September 2, 2003

                                    3 Azrieli Center, 42nd Floor
                                    Tel Aviv, Israel 67023
                                    Attention: Legal Department
                                    Facsimile No.: (972) 3-607-5556


                                       15