Document:

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                                                                     Exhibit 4.5

                          REGISTRATION RIGHTS AGREEMENT

            THIS REGISTRATION RIGHTS AGREEMENT, dated as of November 2, 2004
(this "Agreement"), by and between ZIX CORPORATION, a Texas corporation (the
"Company"), and _________________________, a ________________________ (the
"Investor").

                              W I T N E S S E T H:

            WHEREAS, in connection with the Purchase Agreement (such capitalized
term and all other capitalized terms used herein having the respective meanings
provided herein), the Company has agreed to provide certain registration rights
under the 1933 Act and applicable state securities laws with respect to the
Registrable Securities issuable upon conversion, exercise or redemption of, or
otherwise in connection with, the securities issued pursuant to the Purchase
Agreement;

            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
Holders hereby agree as follows:

            1. DEFINITIONS.

            (a) As used in this Agreement, the terms "Agreement," "Company" and
"Investor" shall have the respective meanings assigned to such terms in the
introductory paragraph of this Agreement.

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

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

            "Additional Registrable Securities" means any shares of Common Stock
which are included within the definition of Registrable Securities but not

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required by this Agreement to be included in any Registration Statement filed
pursuant to Section 2(a)(i) below.

            "Allowed Delay" shall have the meaning provided in Section 2(c)(ii).

            "AMEX" means the American Stock Exchange, Inc.

            "Approved Market" shall have the meaning provided in Section
2(c)(i).

            "Availability Date" shall have the meanings provided in Section
3(m).

            "Closing Warrant" means the Common Stock Purchase Warrant issued by
the Company to the Investor pursuant to the Purchase Agreement and any similar
instrument issued upon transfer or split up thereof.

            "Common Stock" means the Common Stock, par value $0.01 per share, of
the Company.

            "Compensation Event" shall have the meaning provided in Section
2(c)(i).

            "Compensation Period" shall have the meaning provided in Section
2(c)(i).

            "Compensation Rate" shall mean the rate of one percent per month
during the first 30 days in the aggregate in which any one or more Compensation
Periods are in effect and two percent per month thereafter.

            "Conversion Price" shall have the meaning provided in the Note.

            "Holder" means the Investor and each subsequent holder of the Note,
the Warrants, Registrable Securities or Additional Registrable Securities, or
any portion thereof which subsequent holder has rights under this Agreement
assigned to it in accordance with Section 7(c).

            "Initial Registrable Securities Amount" shall have the meaning
provided in Section 2(a)(i).

            "Interest Share Price" shall have the meaning provided in the Note.

            "1934 Act" means the Securities Exchange Act of 1934, as amended,
and the rules and regulations promulgated thereunder.

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            "1933 Act" means the Securities Act of 1933, as amended, and the
rules and regulations promulgated thereunder.

            "NASD" means the National Association of Securities Dealers, Inc.

            "Nasdaq" means the Nasdaq National Market.

            "Note" means the Convertible Note due 2005-2008 issued by the
Company pursuant to the Purchase Agreement.

            "NYSE" means the New York Stock Exchange, Inc.

            "Other Registration Rights Agreements" means the several
Registration Rights Agreements, dated as of the date hereof, by and between the
Company and the several investors parties thereto who purchased Convertible
Notes due 2005-2008 and Common Stock Purchase Warrants issued by the Company.

            "Principal Market" means the Nasdaq or such other U.S. market or
exchange which is the principal market on which the Common Stock is then listed
for trading.

            "Prospectus" means the prospectus forming part of or relating to any
Registration Statement, as amended or supplemented by any prospectus supplement,
with respect to the terms of the offering of any portion of the Registrable
Securities or Additional Registrable Securities covered by such Registration
Statement and by all other amendments and supplements to the prospectus,
including post-effective amendments and all material incorporated by reference
in such prospectus.

            "Purchase Agreement" means the Purchase Agreement, dated as of
November 1, 2004, by and between the Company and the Investor.

            "Purchase Price" when used with respect to a particular Warrant,
shall have the meaning provided in such Warrant.

            "Redemption Warrant" shall have the meaning provided in the Note.

            "register," "registered" and "registration" refer to a registration
made by preparing and filing a registration statement or similar document in
compliance with the 1933 Act, and the declaration or ordering of effectiveness
of such registration statement or document by the SEC.

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            "Registrable Securities" means (i) the Underlying Shares, the
Warrant Shares and the shares of Common Stock or other securities issued or
issuable to each Holder or its permitted transferee or designee (a) upon
conversion of the Note and upon exercise of the Warrants, or (b) upon any
distribution with respect to, any exchange for or any replacement of the Note or
the Warrants, or (c) upon any conversion, exercise or exchange of any securities
issued in connection with any such distribution, exchange or replacement; (ii)
securities issued or issuable upon any stock split, stock dividend,
recapitalization or similar event with respect to the Common Stock or other
securities referred to in clause (i) of this definition; and (iii) any other
security issued as a dividend or other distribution with respect to, in exchange
for, or in replacement of, the Note, the Warrants or the securities referred to
in the preceding clauses of this definition.

            "Registration Insufficiency Event" shall have the meaning provided
in Section 2(a)(i).

            "Registration Period" shall have the meaning provided in Section
3(a).

            "Registration Statement" shall mean any registration statement of
the Company filed under the 1933 Act that covers the resale of any of the
Registrable Securities or Additional Registrable Securities pursuant to the
provisions of this Agreement, amendments and supplements to such Registration
Statement, including post-effective amendments, all exhibits and all material
incorporated by reference in such Registration Statement.

            "SEC" means the U.S. Securities and Exchange Commission.

            "Trading Day" means at any time a day on which the securities
exchange or market that at such time constitutes the Principal Market is open
for general trading of securities.

            "Underlying Shares" means the shares of Common Stock issuable upon
conversion of, or otherwise in respect of or in exchange for, the Note or any
other security (other than the Redemption Warrant) issued in respect of or in
exchange for the Note.

            "VWAP" means for any Trading Day the volume-weighted average price
of the Common Stock on the Principal Market, as reported by Bloomberg Financial
L.P. (based on a Trading Day from 9:30 a.m., Eastern Time, to 4:00 p.m., Eastern
Time) using the AQR function, on such Trading Day.

            "Warrants" means, collectively, the Closing Warrant and the
Redemption Warrant.

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            "Warrant Shares" means the shares of Common Stock issuable upon
exercise of, or otherwise in respect of, the Warrants.

            (d) Capitalized terms used herein but not otherwise defined herein
shall have the respective meanings assigned to such terms in the Purchase
Agreement.

            2. REGISTRATION.

            (a) REGISTRATION STATEMENTS.

            (i) REGISTRABLE SECURITIES. Promptly following the Closing Date
(but, subject to Section 2(a)(iii), no later than 30 days after the Closing
Date), the Company shall prepare and file with the SEC one Registration
Statement on Form S-3 covering the resale of the Registrable Securities in an
amount at least equal to the sum of (1) 150% of the number of Underlying Shares
that would be issuable upon conversion of the Note in full or, in case the Note
were to be redeemed pursuant to Section 2(b) thereof, upon exercise of the
Redemption Warrant in full for cash plus (2) 150% of the number of shares of
Common Stock issuable upon exercise of the Closing Warrant in full for cash,
plus (3) such number of additional Registrable Securities as the Company wishes
to have available to issue in lieu of cash payment of interest on the Note, in
each case in the preceding clauses (1) through (3), determined without regard to
any restrictions on beneficial ownership contained in the Note, the Warrants or
the Purchase Agreement (such sum the "Initial Registrable Securities Amount").
Such Registration Statement also shall cover, to the extent permitted by the
1933 Act and the rules promulgated thereunder (including Rule 416), such
indeterminate number of additional shares of Common Stock resulting from stock
splits, stock dividends or similar transactions with respect to the Registrable
Securities. No securities other than the Registrable Securities and the
securities being registered by the Company in accordance with the Other
Registration Rights Agreements shall be included in the Registration Statement
without the consent of the Holder. If at any time the number of Initial
Registrable Securities specified in clauses (1) and (2) of the definition of
Initial Registrable Securities included in a Registration Statement and
remaining unsold thereunder shall be insufficient to cover the resale of
Registrable Securities in an amount at least equal to 140% of the sum of (x) the
number of Underlying Shares that would be issuable upon conversion in full of
the Note or, in case the Note were to be redeemed pursuant to Section 2(b)
thereof, upon exercise of the Redemption Warrant in full for cash plus (y) the
number of shares of Common Stock issuable upon exercise of the Warrants
outstanding at such time in full for cash, in each case in the preceding clauses
(x) and (y) determined without regard to any restrictions on beneficial
ownership contained in the Note, the Warrants or the Purchase Agreement (a
"Registration Insufficiency Event"), then promptly, but in no event later than
30 days after such insufficiency shall occur, the Company shall file with

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the SEC an additional Registration Statement on Form S-3 (or, if Form S-3 is
not then available to the Company, on such form of registration statement as is
then available to effect a registration for resale of such additional
Registrable Securities) covering such number of shares of Common Stock as shall
be sufficient to cover such amount. Except as set forth above, the requirements
with respect to a subsequent Registration Statement shall be the same as those
applicable to the initial Registration Statement.

            (ii) ADDITIONAL REGISTRABLE SECURITIES. At any time and from time to
time, promptly following the written demand of the Holder following the issuance
of any Additional Registrable Securities or the issuance of any securities
convertible into, exchangeable for, or otherwise entitling the Holder to
acquire, Additional Registrable Securities, and in any event within 30 days
following such demand, the Company shall prepare and file with the SEC a new
Registration Statement on Form S-3 (or, if Form S-3 is not then available to the
Company, on such form of registration statement as is then available to effect a
registration for resale of the Additional Registrable Securities) covering the
resale of the Additional Registrable Securities in an amount equal to the number
of Additional Registrable Securities. Such Registration Statement also shall
cover, to the extent permitted by the 1933 Act and the rules promulgated
thereunder (including Rule 416), such indeterminate number of additional shares
of Common Stock resulting from stock splits, stock dividends or similar
transactions with respect to the Additional Registrable Securities. The
Registration Statement required by this Section 2(a)(ii) (and each amendment or
supplement thereto) shall be provided in accordance with Section 3(c) to the
Holder and its counsel prior to its filing or other submission. Nothing herein
shall limit the Company's obligations or the Holder's rights under Section 6(e)
of the Note, Section 10 of the Closing Warrant or Section 5 of the Redemption
Warrant.

            (iii) CERTAIN OTHER REGISTRATION STATEMENTS. If the Company proposes
to file with the SEC a registration statement (other than on Form S-8) relating
to securities other than the Registrable Securities or Additional Registrable
Securities prior to the deadline for filing such Registration Statement
hereunder, then on or before the date the Company files such other registration
statement with the SEC the Company shall file the Registration Statement
required by Section 2(a)(i) or 2(a)(ii), as the case may be, with the SEC.
Except as required pursuant to the Registration Rights Agreement, dated as of
September 16, 2002, by and among the Company and the parties named therein, or
the Registration Rights Agreement, dated as of September 17, 2002, by and among
the Company and the parties named therein, the Company shall not request
acceleration of effectiveness of such other registration statement unless
simultaneously therewith the Company requests acceleration of effectiveness of
the Registration Statement to the same date and time as so requested for such
other registration statement.

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            (iv) CERTAIN DISCLOSURES. If the Company proposes to include
disclosure in any Registration Statement to be filed with the SEC of the
circumstances under which the Holder acquired the Registrable Securities to be
offered pursuant to such Registration Statement, such disclosure shall include
statements to the effect that the securities being offered may include
Registrable Securities (1) issued upon conversion of, or in lieu of payment of
cash interest on, the Note, (2) issued upon exercise of the Closing Warrant or,
in case of redemption of the Note pursuant to Section 2(b) thereof, upon
exercise of the Redemption Warrant and (3) issued in exchange for, or otherwise
in respect of, the Note or the Warrants.

            (b) EXPENSES. All expenses, other than underwriting discounts and
commissions and other fees and expenses of investment bankers and other than
brokerage commissions, incurred in connection with registrations, filing or
qualifications pursuant to this Agreement, including, without limitation, all
registration, listing and qualifications fees, printers and accounting fees and
the fees and disbursements of counsel for the Company, shall be borne by the
Company.

            (c) EFFECTIVENESS.

            (i) The Company shall use its best efforts to have each Registration
Statement declared effective as soon as practicable after it is filed with the
SEC. If (A) the Company fails to file with the SEC a Registration Statement in
accordance with all of the requirements of this Agreement on or before the date
by which the Company is required to file the Registration Statement pursuant to
Section 2(a)(i) above, (B) the Company fails to file with the SEC the
Registration Statement covering Additional Registrable Securities in accordance
with all of the requirements of this Agreement within 30 days following demand
of the Holder relating to the Additional Registrable Securities to be covered
thereby, (C) the Company fails to file with the SEC a request for acceleration
of effectiveness of a Registration Statement to a time and date not more than 48
hours after the submission of such request, within three Trading Days after the
date the Company learns that no review of the Registration Statement will be
made by the staff of the SEC or that the staff of the SEC has no further
comments on the Registration Statement, as the case may be, (D) the Registration
Statement covering Registrable Securities is not declared effective by the SEC
within 75 days (or 105 days in case the SEC staff reviews such Registration
Statement) following the Closing Date, or the Registration Statement covering
additional Registrable Securities is not declared effective by the SEC within 75
days (or 105 days in case the SEC staff reviews such Registration Statement)
following the date on which a Registration Insufficiency Event occurs, or the
Registration Statement covering Additional Registrable Securities is not
declared effective by the SEC within 75 days (or 105 days in case the SEC staff
reviews such Registration Statement) following demand of the Holder relating to
the Additional Registrable Securities to be covered thereby,

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(E) except as otherwise permitted by Section 2(c)(ii), after a Registration
Statement has been declared effective by the SEC sales cannot be made pursuant
to such Registration Statement or the related Prospectus for any reason,
including, without limitation, by reason of a stop order, misstatements or
omissions in such Registration Statement or Prospectus, or the Company's failure
to update such Registration Statement or Prospectus, excluding any such
inability to make sales that results from an untrue statement of a material fact
in such Registration Statement or Prospectus or omission to state a material
fact required to be stated in such Registration Statement or Prospectus in order
to make the statements therein not misleading, which misstatement or omission
was made by the Holder in written information it furnished to the Company
specifically for inclusion in such Registration Statement or Prospectus which
such information was substantially relied upon by the Company in preparation of
the Registration Statement or Prospectus or any amendment or supplement thereto,
unless the Company shall have failed timely to amend or supplement such
Registration Statement or Prospectus after the Holder shall have corrected such
misstatement or omission, or (F) the Common Stock generally or the Registrable
Securities (or Additional Registrable Securities after issuance) specifically
are not listed or included for quotation on the Nasdaq, the NYSE or the AMEX
(each an "Approved Market"), or trading of the Common Stock is suspended or
halted on the Approved Market which at the time constitutes the Principal Market
for the Common Stock (each of the events in the preceding clauses (A) through
(F) a "Compensation Event"), then the Company will make payments to the Holder
as partial liquidated damages for the minimum amount of damages to the Holder by
reason thereof, and not as a penalty, at the Compensation Rate on the sum of (x)
the outstanding principal amount of, and accrued interest on, the Note held at
such time by the Holder plus (y) the amount, if any, by which the product of (i)
the average of the daily VWAPs for all of the Trading Days during the particular
portion of the Compensation Period for which such computation is being made
times (ii) the number of Warrant Shares issuable upon exercise for cash of the
unexercised portion of the Warrants held at such time by the Holder exceeds the
aggregate Purchase Price of the number of Warrant Shares issuable upon exercise
for cash of the unexercised portion of the Warrants held at such time by the
Holder, plus (z) the product of (1) the number of outstanding Registrable
Securities held at such time by the Holder times (2) the greater of (i) the
average of the daily VWAPs for all of the Trading Days in the particular portion
of the Compensation Period for which such computation is being made and (ii) the
Purchase Price of such Registrable Securities (in the case of Registrable
Securities issued upon exercise of the Warrants), the Conversion Price of such
Registrable Securities (in the case of Registrable Securities issued upon
conversion of the Note) or the Interest Share Price (in the case of Registrable
Securities issued in lieu of payment of cash interest on the Note) for each day
on which any Compensation Event is continuing (the "Compensation Period"). Each
such payment shall be due and payable within five days after the end of each
calendar month of the Compensation Period until the termination of the

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Compensation Period and within five days after such termination. Such payments
shall be in partial compensation to the Holder, and shall not constitute the
Holder's exclusive remedy for any Compensation Event; provided, however, that if
because of a particular Compensation Event the Holder is successful in
recovering on a claim for damages under this Agreement from such Compensation
Event, the amount of Compensation Payments previously paid by the Company to the
Holder with respect to such Compensation Event shall be applied to reduce the
amount of such recovery to the extent of such Compensation Event. A particular
Compensation Period shall terminate upon (v) the filing of the applicable
Registration Statement in the case of clauses (A) and (B) above; (w) the
effectiveness of the applicable Registration Statement in the case of clauses
(C) and (D) above; (x) the date sales can once again be made under the
Registration Statement in the case of clause (E) above, (y) listing or inclusion
and/or trading of the Common Stock on an Approved Market, as the case may be, in
the case of clause (F) above; and (z) in the case of the events described in
clauses (C), (D) or (E) above, the earlier termination of the Registration
Period (as defined in Section 3(a) below), and in each such case any
Compensation Period that commences by reason of the occurrence of such event
shall terminate if at the time no other Compensation Event is continuing. The
amounts payable as partial liquidated damages pursuant to this paragraph shall
be payable in lawful money of the United States. If the Company fails to pay any
liquidated damages pursuant to this Section in full within three days after the
date payable, the Company will pay interest thereon at a rate of 18% per annum
(or such lesser rate that is the highest rate permitted 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. Amounts payable
as partial liquidated damages hereunder shall cease when the Holder no longer
holds any Note, the Warrants, Registrable Securities or Additional Registrable
Securities.

            (ii) For not more than ten consecutive Trading Days or for a total
of not more than 20 Trading Days in any period of 12 consecutive months, the
Company may suspend the use of the Registration Statement(s) that are effective
at such time because the Company determines to delay the disclosure of material
non-public information concerning the Company, if the disclosure of such
information at the time is not, in the good faith opinion of the Company, in the
best interests of the Company or would be unduly detrimental to the Company's
affairs (an "Allowed Delay"); provided, that the Company shall not later than
the date a suspension goes into effect (a) notify the Holder in writing of the
suspension of use of the Registration Statement (but in no event, without the
prior written consent of the Holder, shall the Company disclose to the Holder
any of the material non-public information giving rise to an Allowed Delay), and
(b) advise the Holder in writing to cease all sales under the Registration
Statement until the end of the Allowed Delay. The Company shall notify the
Holder on the date a Registration Statement the use of which has been suspended
under this Section 2(c)(ii) is once again available for use. If the Company
shall have suspended the use of the Registration Statement,

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then no period of Allowed Delay subsequent to such suspension shall commence
sooner than 30 days after the date on which the Company notifies the Holder that
such earlier suspension shall have been lifted.

            3. COMPANY OBLIGATIONS. The Company will use its best efforts to
effect the registration of the Registrable Securities and Additional Registrable
Securities at the times and for the periods specified in this Agreement. The
Company hereby covenants and agrees to:

            (a) use its best efforts to cause such Registration Statement to
become effective and to remain continuously effective for a period (the
"Registration Period") that will terminate upon the earlier of (i) the date on
which all Registrable Securities or Additional Registrable Securities have been
sold (and the Note and the Warrants no longer remain outstanding) and (ii) the
date on which all Registrable Securities or Additional Registrable Securities,
as the case may be, that are issued or may be issued are eligible for sale by
the Holder pursuant to Rule 144(k) promulgated under the 1933 Act;

            (b) prepare and file with the SEC such amendments, post-effective
amendments and prospectus supplements to the Registration Statement and the
Prospectus as may be necessary to keep the Registration Statement effective for
the period specified in Section 3(a) and to comply with the provisions of the
1933 Act and the 1934 Act with respect to the distribution of all Registrable
Securities and Additional Registrable Securities; provided that, at a time
reasonably, but not less than four Business Days, prior to the filing of a
Registration Statement or Prospectus, or any amendments or supplements thereto,
with the SEC the Company will furnish to the Holder copies of all documents
proposed to be filed, which documents will be subject to the comments, if any,
that the Holder provides to the Company reasonably promptly after receipt of
such documents;

            (c) permit counsel designated by the Holder to review each
Registration Statement and Prospectus and all amendments and supplements thereto
no fewer than four Business Days (or as many Business Days as possible if SEC
rules do not allow such time for such review) prior to their filing with the SEC
and not file any document to which such counsel reasonably objects;

            (d) furnish to the Holder 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 any Registration Statement and any amendment
thereto, each preliminary prospectus and Prospectus and each amendment or
supplement thereto, and each letter written by or on behalf of the Company to
the SEC or the staff of the SEC, and each item of correspondence from the SEC or
the staff of the SEC, in each case relating to such Registration Statement
(other than any portion of any thereof which contains information for which the
Company has sought confidential treatment), and (ii) within two Business Days
after the effective date of

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each Registration Statement and within two days after any Prospectus or
amendment or supplement thereto is prepared or filed with the SEC, at least five
copies of a Prospectus, including a preliminary prospectus, and all amendments
and supplements thereto, and such other documents as the Holder may reasonably
request in order to facilitate the disposition of the Registrable Securities and
Additional Registrable Securities owned by the Holder, and thereafter promptly
after the Holder from time to time requests, such additional number of copies
thereof as the Holder may request;

            (e) in the event the Holder selects an underwriter for the offering,
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 underwriter of such offering;

            (f) if the Holder is described in the Registration Statement as an
underwriter, the Company shall use its best efforts to furnish, on the effective
date of the Registration Statement and at periodic intervals thereafter from
time to time on request, (i) an opinion, dated as of such date, from outside
legal counsel representing the Company for purposes of such Registration
Statement, in form, scope and substance as is customarily given in an
underwritten public offering, addressed to the Holder and (ii) a letter, dated
such date, from the Company's independent certified public accountants in form
and substance as is customarily given by independent certified public
accountants to underwriters in an underwritten public offering, addressed to the
Holder;

            (g) use its best efforts to prevent the issuance of any stop order
or other suspension of effectiveness and, if such order is issued, use its best
efforts to obtain the withdrawal of any such order at the earliest possible
moment;

            (h) furnish to the Holder at least five copies of the Registration
Statement and any post-effective amendment thereto, including financial
statements and schedules by reputable overnight courier within three Business
Days after the effective date thereof;

            (i) use its commercially reasonable best efforts to register or
qualify the Registrable Securities or Additional Registrable Securities, as
applicable, for offer and sale under the securities or blue sky laws of such
jurisdictions requested by the Holder prior to the effective date with the SEC
of the applicable Registration Statement and do any and all other reasonable
acts or things necessary or advisable to enable the distribution in such
jurisdictions of the Registrable Securities or Additional Registrable Securities
covered by the Registration Statement; 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(i), (b) subject itself to general

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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.

            (j) without limiting the Company's obligation under the Transaction
Documents to maintain the listing of the Common Stock on an Approved Market,
cause all Registrable Securities or Additional Registrable Securities covered by
a Registration Statement to be listed on each securities exchange, interdealer
quotation system or other market on which similar securities issued by the
Company are then listed;

            (k) cooperate with the Holder to facilitate the timely preparation
and delivery of certificates representing Registrable Securities to be delivered
to a transferee pursuant to a 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 the Holder may request;

            (l) immediately notify the Holder at any time when a Prospectus
relating to the Registrable Securities or Additional Registrable Securities is
required to be delivered under the 1933 Act, upon discovery that, or upon the
happening of any event as a result of which, the Prospectus included in such
Registration Statement, as then in effect, includes an untrue statement of a
material fact or omits to state any material fact required to be stated therein
or necessary to make the statements therein, in the light of the circumstances
under which made, not misleading and promptly prepare and furnish to such holder
a reasonable number of copies of a supplement to or an amendment of such
Prospectus as may be necessary so that, as thereafter delivered to the
purchasers of such Registrable Securities or Additional Registrable Securities,
as applicable, such Prospectus shall not include 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 not misleading in the light of the
circumstances then existing; and

            (m) otherwise comply with all applicable rules and regulations of
the SEC under the 1933 Act and the 1934 Act, take such other actions as may be
reasonably necessary to facilitate the registration of the Registrable
Securities and Additional Registrable Securities, if applicable, hereunder; and
make available to its security holders, as soon as reasonably practicable, but
not later than the Availability Date, an earnings statement covering a period of
at least twelve months, beginning after the effective date of each Registration
Statement, which earnings statement shall satisfy the provisions of Section
11(a) of the 1933 Act. "Availability Date" means, with respect to a particular
Registration Statement, (1) the day on which the Company's Quarterly Report on
Form 10-Q for the fourth

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consecutive fiscal quarter following the fiscal quarter that includes the
effective date of such Registration Statement is due for filing with the SEC
(after giving effect to any extension permitted by Rule 12b-25 under the 1934
Act and claimed by the Company), in case such fourth fiscal quarter is one of
the first three fiscal quarters of the Company's fiscal year, or (2) the day on
which the Company's Annual Report on Form 10-K covering a fiscal year that ends
at the end of the fourth fiscal quarter following the fiscal quarter that
includes the effective date of such Registration Statement is due for filing
with the SEC (after giving effect to any extension permitted by Rule 12b-25
under the 1934 Act and claimed by the Company) in case such fourth fiscal
quarter is the fourth fiscal quarter of the Company's fiscal year.

            4. DUE DILIGENCE REVIEW; INFORMATION. The Company shall make
available, during normal business hours, for inspection and review by the
Holder, advisors to and representatives of the Holder (who may or may not be
affiliated with the Holder and who are reasonably acceptable to the Company),
and any underwriter participating in any disposition of Common Stock on behalf
of the Holder pursuant to the Registration Statement or amendments or
supplements thereto or any blue sky, NASD, or other filing, all financial and
other records, all SEC Filings and other filings with the SEC, and all other
corporate documents and properties of the Company as may be reasonably necessary
for the purpose of establishing a due diligence defense under applicable
securities laws and such other reasonable purposes, and cause the Company's
officers, directors and employees, within a reasonable time period, to supply
all such information reasonably requested by the Holder or any such
representative, advisor or underwriter in connection with such Registration
Statement (including, without limitation, in response to all questions and other
inquiries reasonably made or submitted by any of them), prior to and from time
to time after the filing and effectiveness of the Registration Statement for the
sole purpose of enabling the Holder and such representatives, advisors and
underwriters and their respective accountants and attorneys to conduct initial
and ongoing due diligence with respect to the Company and the accuracy of the
Registration Statement.

            The above to the contrary notwithstanding, the Company shall not
disclose material nonpublic information to the Holder, or to advisors to or
representatives of the Holder, unless prior to disclosure of such information
the Company identifies such information as being material nonpublic information
and provides the Holder, such advisors and representatives with the opportunity
to accept or refuse to accept such material nonpublic information for review.
The Company may, as a condition to disclosing any material nonpublic information
hereunder, require the Holder's advisors and representatives to enter into a
confidentiality agreement (including an agreement with such advisors and
representatives prohibiting them from trading in Common Stock during such period

                                      -13-
<PAGE>

of time as they are in possession of material nonpublic information) in form
reasonably satisfactory to the Company and the Holder.

            5. OBLIGATIONS OF THE HOLDER.

            (a) The Holder shall furnish in writing to the Company such
information regarding itself, the Registrable Securities or Additional
Registrable Securities, as applicable, held by it and the intended method of
disposition of the Registrable Securities or Additional Registrable Securities,
as applicable, held by it, as shall be required by the 1933 Act to effect the
registration of such Registrable Securities or Additional Registrable
Securities, as applicable, and shall execute such documents in connection with
such registration as the Company may reasonably request. At least five Business
Days prior to the first anticipated filing date of any Registration Statement
(or such shorter period as may be agreed to by the Holder), the Company shall
notify the Holder of the information the Company requires from the Holder if the
Holder's Registrable Securities or Additional Registrable Securities are to be
included in the Registration Statement.

            (b) The Holder, by its acceptance of the Registrable Securities and
Additional Registrable Securities, if any, agrees to cooperate with the Company
as reasonably requested by the Company in connection with the preparation and
filing of a Registration Statement hereunder, unless the Holder has notified the
Company in writing of its election to exclude all of its Registrable Securities
or Additional Registrable Securities, as applicable, from the Registration
Statement.

            (c) The Holder agrees that, upon receipt of any notice from the
Company of the happening of any event rendering a Registration Statement no
longer effective or available for use by the Holder, the Holder will immediately
discontinue disposition of Registrable Securities or Additional Registrable
Securities pursuant to the Registration Statement covering such Registrable
Securities or Additional Registrable Securities, until the Holder's receipt of
the copies of the supplemented or amended Prospectus filed with the SEC and
declared effective and, if so directed by the Company, the Holder shall deliver
to the Company (at the expense of the Company) or destroy all copies in the
Holder's possession, or instruct its agents or other representatives to deliver
to the Company (at the Company's expense) or destroy all copies in such Agents'
or other representatives' possession, in either case of the Prospectus covering
the Registrable Securities or Additional Registrable Securities, as applicable,
current at the time of receipt of such notice.

            6. INDEMNIFICATION.

            (a) INDEMNIFICATION BY COMPANY. The Company agrees to indemnify and
hold harmless, to the fullest extent permitted by law, the Holder,

                                      -14-
<PAGE>

each investment advisor and investment sub-advisor of the Holder and each of
their respective officers, directors, partners, members and employees and each
person who controls the Holder (within the meaning of the 1933 Act) against all
losses, claims, damages, liabilities, costs (including, without limitation,
reasonable attorney's fees) and expenses imposed on such person caused by (i)
any untrue or alleged untrue statement of a material fact contained in any
Registration Statement, Prospectus or any preliminary prospectus or any
amendment or supplement thereto or any omission or alleged omission to state
therein a material fact required to be stated therein or necessary to make the
statements therein not misleading, except insofar as the same are based upon any
information furnished in writing to the Company by the Holder, expressly for use
therein, or (ii) any violation by the Company of any federal, state or common
law, rule or regulation applicable to the Company in connection with any
Registration Statement, Prospectus or any preliminary prospectus, or any
amendment or supplement thereto, and shall reimburse in accordance with
subparagraph (c) below, each of the foregoing persons for any legal and any
other expenses reasonably incurred in connection with investigating or defending
any such claims. The foregoing is subject to the condition that, insofar as the
foregoing indemnities relate to any untrue statement, alleged untrue statement,
omission or alleged omission made in any preliminary prospectus or Prospectus
that is eliminated or remedied in any Prospectus or amendment or supplement
thereto, the above indemnity obligations of the Company shall not inure to the
benefit of any indemnified party if a copy of such corrected Prospectus or
amendment or supplement thereto had been timely provided to such indemnified
party and was not sent or given by such indemnified party at or prior to the
time such action was required of such indemnified party by the 1933 Act and if
delivery of such Prospectus or amendment or supplement thereto would have
eliminated (or been a sufficient defense to) any liability of such indemnified
party with respect to such statement or omission. Indemnity under this Section
5(a) shall remain in full force and effect regardless of any investigation made
by or on behalf of any indemnified party and shall survive the transfer of the
Registrable Securities and Additional Registrable Securities.

            (b) INDEMNIFICATION BY HOLDER. In connection with any registration
pursuant to the terms of this Agreement, the Holder will furnish to the Company
in writing such information as required by the 1933 Act concerning the Holder or
the proposed manner of distribution for use in connection with any Registration
Statement or Prospectus and agrees to indemnify and hold harmless, to the
fullest extent permitted by law, the Company, its directors, officers, and each
person who controls the Company (within the meaning of the 1933 Act) against any
losses, claims, damages, liabilities and expense (including reasonable
attorney's fees) resulting from any untrue statement of a material fact in the
Registration Statement or Prospectus or preliminary prospectus or amendment or
supplement thereto or any omission of a material fact required to be stated in
the Registration Statement or Prospectus or preliminary prospectus or amendment
or supplement

                                      -15-
<PAGE>

thereto necessary to make the statements therein not misleading, to the extent,
but only to the extent that such untrue statement is contained or such omission
is made in any information about the Holder furnished in writing by such Holder
to the Company specifically for inclusion in such Registration Statement or
Prospectus or amendment or supplement thereto and that such information was
substantially relied upon by the Company in preparation of the Registration
Statement or Prospectus or any amendment or supplement thereto. In no event
shall the liability of the Holder be greater in amount than the dollar amount of
the proceeds (net of the cost of the Registrable Securities and Additional
Registrable Securities sold and all expenses paid by the Holder and not
reimbursed by the Company and the amount of any damages the Holder has otherwise
been required to pay by reason of such untrue statement or omission) received by
the Holder upon the sale of the Registrable Securities or Additional Registrable
Securities included in the Registration Statement giving rise to such
indemnification obligation.

            (c) CONDUCT OF INDEMNIFICATION PROCEEDINGS. Any person entitled to
indemnification hereunder shall (i) give prompt notice to the indemnifying party
of any claim with respect to which it seeks indemnification, (ii) permit such
indemnifying party to assume the defense of such claim with counsel reasonably
satisfactory to the indemnified party and (iii) by notice to the indemnifying
party, require the indemnifying party to assume the defense of such claim with
counsel reasonably satisfactory to the indemnified party; provided, however,
that any person entitled to indemnification hereunder shall have the right to
employ separate counsel and to participate in the defense of such claim, but the
fees and expenses of such counsel shall be at the expense of such person unless
(a) the indemnifying party has agreed to pay such fees or expenses, or (b) the
indemnifying party shall have failed to assume the defense of such claim and
employ counsel reasonably satisfactory to such person or (c) in the reasonable
judgment of any such person, based upon written advice of its counsel, a
conflict of interest exists between such person and the indemnifying party with
respect to such claims (in which case, if the person notifies the indemnifying
party in writing that such person elects to employ separate counsel at the
expense of the indemnifying party, the indemnifying party shall not have the
right to assume the defense of such claim on behalf of such person); and
provided, however, further, that the failure of any indemnified party to give
notice as provided herein shall not relieve the indemnifying party of its
obligations hereunder, except to the extent that such failure to give notice
shall materially adversely affect the indemnifying party in the defense of any
such claim or litigation. It is understood that the indemnifying party shall
not, in connection with any proceeding in the same jurisdiction, be liable for
fees or expenses of more than one separate firm of attorneys at any time for all
such indemnified parties. No indemnifying party will, except with the consent of
each indemnified party, consent to entry of any judgment or enter into any
settlement that does not include as an unconditional term thereof the giving by
the claimant or

                                      -16-
<PAGE>

plaintiff to such indemnified party of a release from all liability in respect
of such claim or litigation.

            (d) CONTRIBUTION. If for any reason the indemnification provided for
in the preceding paragraphs (a) and (b) is unavailable to an indemnified party
or insufficient to hold it harmless, other than as expressly specified therein,
then the indemnifying party shall contribute to the amount paid or payable by
the indemnified party as a result of such loss, claim, damage or liability in
such proportion as is appropriate to reflect the relative fault of the
indemnified party and the indemnifying party, as well as any other relevant
equitable considerations. No person guilty of fraudulent misrepresentation
within the meaning of Section 11(f) of the 1933 Act shall be entitled to
contribution from any person not guilty of such fraudulent misrepresentation. In
no event shall the contribution obligation of a holder of Registrable Securities
or Additional Registrable Securities be greater in amount than the dollar amount
of the proceeds (net of the cost of the Registrable Securities or Additional
Registrable Securities sold and all expenses paid by such holder and not
reimbursed by the Company and the amount of any damages such holder has
otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission) received by it upon the sale of the
Registrable Securities or Additional Registrable Securities giving rise to such
contribution obligation.

            7. MISCELLANEOUS.

            (a) AMENDMENTS AND WAIVERS. Prior to the date the Registration
Statement contemplated by Section 2(a)(i) is first ordered effective by the SEC
or at any time thereafter during the Registration Period that the Registration
Statement or Prospectus shall not be effective or available for use by the
Holder to sell Registrable Securities, this Agreement may be amended only by a
writing signed by the Company and the Holder. Except as provided in the
immediately preceding sentence, the Company may take any action herein
prohibited, or omit to perform any act herein required to be performed by it, in
any such case after the Registration Statement covering the Initial Registrable
Securities Amount is declared effective by the SEC only if the Company shall
have obtained the written consent to such amendment, action or omission to act,
of the Holder and holders under the Other Registration Rights Agreements who
hold, directly or indirectly, at least 66 2/3% of the aggregate number of
Registrable Securities and Additional Registrable Securities (as defined herein
or in the Other Registration Rights Agreements) held by the Holder and such
other holders.

            (b) NOTICES. All notices and other communications provided for or
permitted hereunder shall be made as set forth in Section 8.4 of the Purchase
Agreement or, in the case of any Holder other than the Investor, to such Holders

                                      -17-
<PAGE>

address set forth in the instrument signed by such Holder pursuant to Section
7(c) or such other address as provided by such Holder by notice to the Company.

            (c) ASSIGNMENTS AND TRANSFERS BY HOLDER. This Agreement and the
rights and obligations of the Holder hereunder may be assigned or transferred in
whole to any transferee or assignee of the Note, the Warrants, the Registrable
Securities or the Additional Registrable Securities or in part to any transferee
or assignee of any portion thereof, except as otherwise set forth herein. The
Holder may make such assignment or transfer to any transferee or assignee of the
Note, the Warrants, the Registrable Securities or the Additional Registrable
Securities; provided, that (i) such transfer is made expressly subject to this
Agreement and the transferee agrees in writing to be bound by the terms and
conditions hereof, and (ii) the Company is provided with written notice of such
assignment.

            (d) ASSIGNMENTS AND TRANSFERS BY THE COMPANY. This Agreement may not
be assigned by the Company without the prior written consent of the Holder but,
in any case of any successor-in-interest to the Company or any Person other than
the Company who is an issuer of Registrable Securities or Additional Registrable
Securities, such successor-in-interest or other issuer, shall assume, jointly
and severally with the Company, the rights and duties of the Company hereunder,
in the event of a merger or consolidation of the Company with or into another
corporation or the sale of all or substantially all of the Company's assets (and
it shall be a condition to any such merger, consolidation or sale that such
successor-in-interest or other issuer assume in writing all obligations
hereunder jointly and severally with the Company as provided herein and in the
Note and the Warrants).

            (e) BENEFITS OF THE AGREEMENT. The terms and conditions of this
Agreement shall inure to the benefit of and be binding upon the respective
permitted successors and assigns of the parties. Nothing in this Agreement,
express or implied, is intended to confer upon any party other than the parties
hereto or their respective permitted successors and assigns any rights,
remedies, obligations, or liabilities under or by reason of this Agreement,
except as expressly provided in this Agreement.

            (f) COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

            (g) TITLES AND SUBTITLES. The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

                                      -18-
<PAGE>

            (h) SEVERABILITY. If one or more provisions of this Agreement are
held to be unenforceable under applicable law, such provision shall be excluded
from this Agreement and the balance of this Agreement shall be interpreted as if
such provision were so excluded and shall be enforceable in accordance with its
terms to the fullest extent permitted by law.

            (i) FURTHER ASSURANCES. The parties shall execute and deliver all
such further instruments and documents and take all such other actions as may
reasonably be required to carry out the transactions contemplated hereby and to
evidence the fulfillment of the agreements herein contained.

            (j) ENTIRE AGREEMENT. This Agreement, together with the Purchase
Agreement, the Note and the Warrants and documents contemplated thereby, is
intended by the parties as a final expression of their agreement and intended to
be a complete and exclusive statement of the agreement and understanding of the
parties hereto in respect of the subject matter contained herein. This
Agreement, together with the Purchase Agreement, the Note and the Warrants and
documents contemplated thereby, supersedes all prior agreements and
understandings between the parties with respect to such subject matter.

            (k) APPLICABLE LAW. This Agreement shall be governed by, and
construed in accordance with, the laws of the State of New York without regard
to principles of conflicts of law.

                            [Signature Page Follows]

                                      -19-
<PAGE>

            IN WITNESS WHEREOF, the parties have caused this Registration Rights
Agreement to be duly executed by their respective officers or other
representatives thereunto duly authorized as of the date first written above.

                                           ZIX CORPORATION

                                           By: _________________________________
                                               Name:
                                               Title:

                                           [                      ]

                                           By: _________________________________
                                               Name:
                                               Title:

                                      -20-<PAGE>

                                                                     Exhibit 4.6

                               SECURITY AGREEMENT

            THIS SECURITY AGREEMENT, dated as of November 2, 2004 (this
"Agreement"), made by ZIX CORPORATION, a Texas corporation (the "Grantor"), to
LAW OFFICES OF BRIAN W PUSCH, as collateral agent (in such capacity, the
"Collateral Agent") on behalf of the Holders (such capitalized term and all
other capitalized terms used in this Agreement having the respective meanings
provided in this Agreement).

                              W I T N E S S E T H:

            WHEREAS, the Grantor and the several Buyers are parties to the
several Purchase Agreements, pursuant to which, among other things, the Buyers
have agreed to purchase $20,000,000 aggregate principal amount of Notes of the
Grantor;

            WHEREAS, in connection with the transactions contemplated by the
Purchase Agreements, the Grantor has agreed to grant to the Collateral Agent a
security interest in certain of its property, assets and rights; and

            WHEREAS, it is a condition precedent to the several obligations of
the Buyers to purchase their respective Notes and Warrants pursuant to the
Purchase Agreements that the Grantor shall have executed and delivered this
Security Agreement to the Collateral Agent for the ratable benefit of the
Holders and deposited $10,000,000.00 with the Collateral Agent as Collateral;

            NOW, THEREFORE, in consideration of the premises and to induce the
Buyers to purchase their respective Notes and Warrants, the Grantor hereby
agrees with the Collateral Agent, for the ratable benefit of the Holders, as
follows:

            1. DEFINITIONS.

            (a) As used in this Agreement, the terms "Agreement", "Grantor" and
"Collateral Agent" shall have the respective meanings assigned to such terms in
the introductory paragraph of and the recitals to this Agreement.

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

            (c) Capitalized terms used herein without definition shall have the
respective meanings assigned to such terms in the Notes.

<PAGE>

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

            "Affiliate" means, with respect to any Person, any other Person that
      directly, or indirectly through one or more intermediaries, controls, is
      controlled by or is under common control with the subject Person. For
      purposes of this definition, "control" (including, with correlative
      meaning, the terms "controlled by" and "under common control with"), as
      used with respect to any Person, shall mean the possession, directly or
      indirectly, of the power to direct or cause the direction of the
      management and policies of such Person, whether through the ownership of
      voting securities or by contract or otherwise.

            "Business Day" means any day other than a Saturday, Sunday or a day
      on which commercial banks in The City of New York or Dallas, Texas are
      authorized or required by law or executive order to remain closed.

            "Buyer" means any of the several buyers party to a Purchase
      Agreement.

            "Code" means the Uniform Commercial Code as from time to time in
      effect in the State of Texas.

            "Collateral" means each of the following, whether now existing or
      hereafter arising:

                  (1) the funds deposited with the Collateral Agent pursuant to
            Section 3;

                  (2) the Collateral Account and each and every General
            Intangible relating thereto;

                  (3) all cash, securities and other property at any time held
            in the Collateral Account;

                  (4) all cash, securities, rights and other property at any
            time or from time to time received, receivable or otherwise
            distribute in respect of the cash and other property held in the
            Collateral Account;

                  (5) all cash, securities, rights and other property at any
            time and from time to time received, receivable or otherwise
            distributed in respect of the Collateral;

                                      -2-
<PAGE>

                  (6) all insurance policies, surety bonds or indemnities to the
            extent they relate to items (1) through (5) above;

                  (7) all books, ledgers, books of account, records, writings,
            databases, information and other property relating to, used or
            useful in connection with, evidencing, embodying, incorporating, or
            referring to any of the foregoing; and

                  (8) to the extent not otherwise included, all Proceeds,
            products, rents, issues, profits and returns of and from any and all
            of the foregoing.

            "Collateral Account" means the account maintained at Citibank, N.A.
      for the ratable benefit of the Holders which is identified in Section 3
      and entitled "Zix Noteholder Collateral Account" and any successor or
      replacement account.

            "Earnings Release Condition" means that the Grantor shall have had
      consolidated net income in each of two consecutive fiscal quarters, the
      earlier of which shall begin after the Issuance Date, determined from the
      Grantor's consolidated financial statements filed with the SEC, prepared
      in accordance with generally accepted accounting principles applied on a
      basis consistent with those used in the preparation of the Grantor's
      annual financial statements for 2003, but excluding any extraordinary
      item, including, without limitation, any item of extraordinary income or
      gain.

            "Event of Default" means:

                  (1) the failure by the Grantor to perform in any material
            respect any obligation of the Grantor under this Agreement as and
            when required by this Agreement; or

                  (2) any representation or warranty made by the Grantor
            pursuant to this Agreement shall have been untrue in any material
            respect when made or deemed to have been made; or

                  (3) any Event of Default, as that term is defined in any of
            the Notes.

            "General Intangibles" shall have the meaning assigned to such term
      under the Code.

            "Holder" means any Buyer or any holder from time to time of any
      Note.

            "Indemnified Person" shall have the meaning provided in Section
      5(l).

                                      -3-
<PAGE>

            "Issuance Date" means the date on which the Notes are initially
      issued.

            "Lien" shall mean any lien, mortgage, security interest, chattel
      mortgage, pledge or other encumbrance (statutory or otherwise) of any kind
      securing satisfaction or performance of an obligation, including any
      agreement to give any of the foregoing, any conditional sales or other
      title retention agreement, any lease in the nature thereof, and the filing
      of or the agreement to give any financing statement under the Code of any
      jurisdiction or similar evidence of any encumbrance, whether within or
      outside the United States.

            "Majority Holders" means at any time such of the holders of the
      Notes who hold Notes which, based on the outstanding principal amounts
      thereof, represent two-thirds of the aggregate outstanding principal
      amount of the Notes at such time.

            "Notes" means the Grantor's Convertible Notes due 2005-2008 issued
      pursuant to the Purchase Agreements.

            "Obligations" means:

                  (1) the full and prompt payment when due of all obligations
            and liabilities to the Holders, whether now existing or hereafter
            arising, under the Transaction Documents and the due performance and
            compliance with the terms of the Transaction Documents;

                  (2) any and all sums advanced by the Collateral Agent or any
            Holder in order to preserve the Collateral or to preserve the
            Security Interest;

                  (3) in the event of any proceeding for the collection or
            enforcement of any obligations or liabilities of the Grantor
            referred to in the immediately preceding clauses (1) and (2) in
            accordance with the terms of the Transaction Documents, the
            reasonable expenses of re-taking, holding, preparing for sale,
            selling or otherwise disposing of or realizing on the Collateral, or
            of any other exercise by the Collateral Agent of its rights
            hereunder, together with reasonable attorneys' fees and court costs;
            and

                  (4) any amounts for which the Collateral Agent or any Holder
            is entitled to indemnification under Section 5(f).

                                      -4-
<PAGE>

            "Person" means any natural person, corporation, partnership, limited
      liability company, trust, incorporated organization, unincorporated
      association or similar entity or any government, governmental agency or
      political subdivision.

            "Proceeds" shall have the meaning assigned to such term under the
      Code.

            "Purchase Agreements" means the several Purchase Agreements, dated
      as of November 1, 2004, by and between the Grantor and the respective
      Buyer party thereto pursuant to which the Grantor issued the Notes.

            "Release Certificate" means a certificate, signed by the Grantor's
      Chief Financial Officer, stating

                  (1) that such certificate is being furnished pursuant to
            Section 15(b) of this Agreement;

                  (2) that the signer has reviewed the consolidated quarterly
            financial statements of the Grantor identified in, and copies of
            which are attached to, such, certificate;

                  (3) that the person signing such certificate has reviewed the
            requirements of Section 15(b) of this Agreement; and

                  (4) that the Earnings Release Condition has been satisfied and
            setting forth the amount for each such quarter on which the
            satisfaction of the Earnings Release Condition is based.

            "Security Interest" means the security interest granted in the
      Collateral pursuant to this Agreement.

            "Subsidiary" means any corporation or other entity of which a
      majority of the capital stock or other ownership interests having ordinary
      voting power to elect a majority of the board of directors or other
      Persons performing similar functions are at the time directly or
      indirectly owned by the Grantor.

            "Transaction Documents" means the Notes, the Purchase Agreements,
      the Registration Rights Agreements, this Agreement, the Warrants, the
      Redemption Warrants, the Other Redemption Warrants and the other
      agreements, instruments and documents contemplated hereby and thereby.

            2. GRANT OF SECURITY INTEREST. As collateral security for the prompt
and complete payment and performance of the Obligations and for the other
purposes provided in this Agreement, the Grantor hereby grants to the Collateral

                                      -5-
<PAGE>

Agent for the ratable benefit of the Holders a first priority security interest
in all of the Collateral.

            3. DEPOSIT OF COLLATERAL WITH COLLATERAL AGENT; COLLATERAL ACCOUNT.

            (a) On the Issuance Date, the Grantor shall transfer or arrange the
transfer of $10,000,000 of the Grantor's funds to the Collateral Agent as
Collateral hereunder. Such transfer shall be made in immediately available funds
to the following account:

            Citibank, N.A.
            153 East 53rd Street
            New York, New York
            ABA No.:  021000089

            For credit to Account No. 3717 9446
            Brian W. Pusch Attorney Trust Account

            (b) The Collateral Agent shall promptly, but in no event later than
five Business Days, after the Issuance Date establish a separate account at
Citibank, N.A. as the Collateral Account entitled "Zix Noteholder Collateral
Account" and deposit and hold therein all funds transferred by the Grantor to
the Collateral Agent pursuant to Section 3(a) until such funds are disbursed by
the Collateral Agent as provided in this Agreement. The Collateral Account shall
be established for the benefit of the Grantor, but subject at all times to this
Agreement and the Security Interest. The Collateral Account shall be an
interest-bearing account. All interest earned on the Collateral Account shall be
added to, and held in, the Collateral Account and shall be Collateral and held
by the Collateral Agent until released as provided in this Agreement.

            (c) The Collateral Account shall at all times be under the sole
dominion and control of, and shall at all times be segregated from any other
custodial, collateral, or other accounts maintained by, or under the dominion
and control of, the Collateral Agent. It shall be a term and condition of the
Collateral Account that, notwithstanding any term or condition to the contrary
in the Transaction Documents or in any other agreement relating to the
Collateral Account, and except as otherwise provided in Section 15 of this
Agreement, no Collateral (including proceeds thereof) shall be paid or released
from the Collateral Account to or for the account of, or withdrawn by or for the
account of, and no entitlement orders with respect to any of the Collateral
shall be given to the bank at which the Collateral Account is maintained by, the
Grantor or any other Person other than the Collateral Agent as provided herein.

                                      -6-
<PAGE>

            (d) Subject to the provisions of this Agreement, the Collateral
Account shall be registered in the name of the Collateral Agent on the books and
records of the bank at which the Collateral Account is maintained, the
Collateral Agent shall be identified on such books and records as the holder of
all financial assets from time to time held in or credited to the Collateral
Account, and the Collateral Agent shall have the sole right to make withdrawals
from the Collateral Account or otherwise exercise any other rights with respect
to any Collateral from time to time credited thereto or on deposit therein.

            (e) The Collateral Account shall be subject to such applicable laws,
and such applicable regulations of any appropriate banking or governmental
authority, as may now or hereafter be in effect, including, without limitation,
any applicable regulations of the Board of Governors of the Federal Reserve
System.

            4. REPRESENTATIONS AND WARRANTIES. The Grantor hereby represents and
warrants that:

            (a) TITLE; NO OTHER LIENS. Except for the Lien granted to the
Collateral Agent for the ratable benefit of the Holders pursuant to this
Agreement, the Grantor owns and has good and marketable title to each item of
the Collateral free and clear of any and all Liens or claims of others. No
security agreement, financing statement or other public notice with respect to
all or any part of the Collateral is on file or of record in any public office,
except such as may have been filed in favor of the Collateral Agent, for the
ratable benefit of the Holders, pursuant to this Agreement.

            (b) PERFECTED FIRST PRIORITY LIENS. The Liens granted pursuant to
this Agreement will constitute upon the completion of all the filings or notices
listed in SCHEDULE I hereto, perfected Liens on all Collateral in favor of the
Collateral Agent for the benefit of the Holders, which are prior to all other
Liens on such Collateral and which are enforceable as such against all Persons.

            (c) CHIEF EXECUTIVE OFFICE. The Grantor's chief executive office and
chief place of business is located at 2711 N. Haskell Avenue, Suite 2300, LB 36,
Dallas, Texas 75204.

            (d) POWER AND AUTHORITY. The Grantor has full power, authority and
legal right to grant the Collateral Agent the Lien on the Collateral pursuant to
this Agreement.

            (e) APPROVALS, FILINGS, ETC. No authorization, approval or consent
of, or filing, registration, recording or other action with, any United States
or foreign court, governmental body, regulatory agency, self-regulatory
organization, or stock exchange or market, the stockholders of the Grantor or
any

                                      -7-
<PAGE>
other Person, is required to be obtained or made by the Grantor or any
Subsidiary (x) for the grant by the Grantor of the Security Interest in the
Collateral pursuant to this Agreement, (y) to perfect the Security Interest
purported to be created by this Agreement, or (z) for the exercise of the
Collateral Agent's rights and remedies provided herein or at law, in each case
except as has been obtained or made.

            5. COVENANTS. The Grantor covenants and agrees with the Collateral
Agent that from and after the date of this Agreement until the payment or
performance in full by the Grantor of all of the Obligations:

            (a) LIMITATION ON LIENS ON COLLATERAL. The Grantor (x) will not
create, incur or permit to exist, will defend the Collateral against, and will
take such other action as is necessary to remove, any Lien or claim on or to the
Collateral, other than the Security Interest created hereby, and (y) will defend
the right, title and interest of the Collateral Agent in and to any of the
Collateral against the claims and demands of all Persons.

            (b) LIMITATIONS ON DISPOSITIONS OF COLLATERAL. The Grantor will not
sell, transfer, lease, assign, grant any participation or interest in, or
otherwise dispose of, any of the Collateral to any Person, including, without
limitation, any Subsidiary or Affiliate of the Grantor, or attempt, offer or
contract to do so.

            (c) NOTICES. The Grantor will advise the Collateral Agent within two
Business Days of the occurrence thereof, in reasonable detail, at its address in
accordance with Section 16, (i) of any Lien (other than Liens permitted
hereunder) on, or claim asserted against, any of the Collateral, (ii) of any
Event of Default or any event which, with notice or the lapse of time, or both,
would become an Event of Default and (iii) of the occurrence of any other event
which could reasonably be expected to have a material adverse effect on the
Collateral, the Security Interest or the rights of the Collateral Agent
hereunder.

            (d) CHANGES IN LOCATIONS, NAME, ETC. The Grantor will not

            (1) change the location of its chief executive office/chief place of
      business from that specified in Section 4(c), or

            (2) change its name, identity or corporate structure to such an
      extent that any financing statement filed in connection with this
      Agreement and naming the Collateral Agent as secured party would become
      misleading or invalid,

unless in any such case it shall have given the Collateral Agent at least 30
days prior written notice thereof and, prior to such action or event, shall have
taken

                                      -8-
<PAGE>

appropriate action satisfactory to the Collateral Agent to preserve and protect
the Collateral Agent's security interest under this Agreement.

            (e) SUBSIDIARIES. This Agreement is entered into on behalf of and
for the benefit of the Grantor. The Subsidiaries and the Affiliates of the
Grantor have no ownership or other rights in the Collateral. The Grantor will
not permit any Subsidiary or any Affiliate of the Grantor to have any ownership
or other rights in or to exercise any control over the Collateral.

            (f) INDEMNIFICATION. The Grantor agrees to indemnify and hold
harmless the Collateral Agent and each Holder and their respective officers,
directors, Affiliates, agents, members, shareholders and investment advisors
(each, an "Indemnified Person") from and against any and all claims, demands,
losses, judgments and liabilities (including liabilities for penalties) of
whatsoever kind or nature, and to reimburse the Collateral Agent and each Holder
for all costs and expenses, including reasonable attorneys' fees and expenses,
arising out of or resulting from this Agreement, including any breach hereof or
Event of Default hereunder, or the exercise by the Collateral Agent or any
Holder, as the case may be, of any right or remedy granted to it hereunder or
under the other Transaction Documents under applicable law; provided, however,
that the Grantor shall not be required to indemnify a particular Indemnified
Person to the extent any claim, demand, loss, judgment, liability, cost or
expense is determined by final judgment (not subject to further appeal) of a
court of competent jurisdiction to have arisen primarily from the gross
negligence or willful misconduct of such Indemnified Person. In no event shall
any Indemnified Person other than the Collateral Agent have any liability or
obligation to the Grantor under this Agreement or applicable law (liability
under which the Grantor hereby waives) for any matter or thing in connection
with this Agreement, and in no event shall the Collateral Agent be liable, in
the absence of a determination of gross negligence or willful misconduct on its
part by final judgment (not subject to further appeal) of a court of competent
jurisdiction, for any matter or thing in connection with this Agreement other
than to account for moneys actually received by it in accordance with the terms
hereof. If and to the extent that the obligations of the Grantor under this
Section 5(f) are unenforceable for any reason, the Grantor hereby agrees to make
the maximum contribution to the payment and satisfaction of such obligations
which is permissible under applicable law.

            6. COLLATERAL AGENT'S POWERS.

            (a) POWERS. The Grantor hereby irrevocably constitutes and appoints
the Collateral Agent and any officer or agent thereof or investment advisor
thereto, with full power of substitution, as its true and lawful
attorney-in-fact with full irrevocable power and authority in the place and
stead of the Grantor and in the name of the Grantor or in its own name, from
time to time in the Collateral Agent's discretion, during any period in which an
Event of Default is continuing, for

                                      -9-
<PAGE>

the purpose of carrying out the terms of this Agreement, to take any and all
appropriate action and to execute any and all documents and instruments which
may be necessary or desirable to accomplish the purposes of this Agreement, and,
without limiting the generality of the foregoing, the Grantor hereby gives the
Collateral Agent and each such officer, agent and investment advisor the power
and right, on behalf of the Grantor, without notice to or assent by the Grantor,
except any notice required by law, to do the following:

            (i) to take possession of and endorse and collect any checks,
      drafts, notes, acceptances or other instruments for the payment of moneys
      due under or with respect to any Collateral and to file any claim or to
      take any other action or proceeding in any court of law or equity or
      otherwise deemed appropriate by the Collateral Agent for the purpose of
      collecting any and all such moneys due under or with respect to any such
      Collateral whenever payable, in each case in the name of the Grantor or
      its own name, or otherwise;

            (ii) to pay or discharge taxes and liens levied or placed on or
      threatened against the Collateral and to pay all or any part of the
      premiums therefor and the costs thereof; and

            (iii) (A) to direct any party liable for any payment under any of
      the Collateral to make payment of any and all moneys due or to become due
      thereunder directly to the Collateral Agent or as the Collateral Agent
      shall direct; (B) to ask or demand for, collect, receive payment of and
      receipt for, any and all moneys, claims and other amounts due or to become
      due at any time in respect of or arising out of any Collateral; (C) to
      sign and endorse any invoices, freight or express bills, bills of lading,
      storage or warehouse receipts, drafts against debtors, assignments,
      verifications, notices and other documents in connection with any of the
      Collateral; (D) to commence and prosecute any suits, actions or
      proceedings at law or in equity in any court of competent jurisdiction to
      collect the Collateral or any thereof and to enforce any other right in
      respect of any Collateral; (E) to defend any suit, action or proceeding
      brought against the Grantor with respect to any Collateral; (F) to settle,
      compromise or adjust any suit, action or proceeding described in clause
      (E) above and, in connection therewith, to give such discharges or
      releases as the Collateral Agent may deem appropriate; and (G) generally,
      to sell, transfer, pledge and make any agreement with respect to or
      otherwise deal with any of the Collateral as fully and completely as
      though the Collateral Agent were the absolute owner thereof for all
      purposes, and to do, at the Collateral Agent's option and the Grantor's
      expense, at any time, or from time to time, all acts and things which the
      Collateral Agent deems necessary to protect, preserve or realize upon the
      Collateral and the Collateral Agent's Liens thereon and to effect the
      intent of this Agreement, all as fully and effectively as the Grantor
      might do.

                                      -10-
<PAGE>

The Grantor hereby ratifies all that said attorneys shall lawfully do or cause
to be done by virtue hereof. This power of attorney is a power coupled with an
interest and shall be irrevocable until the Grantor shall have paid and
performed in full all of the Obligations.

            (b) OTHER POWERS. The Grantor also authorizes the Collateral Agent,
from time to time during any period in which an Event of Default is continuing,
to execute, in connection with the sale provided for herein, any endorsements,
assignments or other instruments of conveyance or transfer with respect to the
Collateral.

            (c) NO DUTY ON COLLATERAL AGENT'S PART. The powers conferred on the
Collateral Agent hereunder are solely to protect the Collateral Agent's
interests in the Collateral for the pro rata benefit of the Holders and shall
not impose any duty upon the Collateral Agent to exercise any such powers. The
Collateral Agent shall be accountable only for amounts that it actually receives
as a result of the exercise of such powers, and neither it nor any of its
officers, directors, employees or agents shall be responsible to the Grantor for
any act or failure to act hereunder, except for their own gross negligence or
willful misconduct.

            7. PERFORMANCE BY COLLATERAL AGENT OF GRANTOR'S OBLIGATIONS. If the
Grantor fails to perform or comply with any of its agreements contained herein
and the Collateral Agent, as provided for by the terms of this Agreement and
following reasonable notice to the Grantor, may itself perform or comply, or
otherwise cause performance or compliance, with such agreement, and the expenses
of the Collateral Agent incurred in connection with such performance or
compliance shall be payable by the Grantor to the Collateral Agent on demand and
shall constitute Obligations secured hereby.

            8. REMEDIES IN GENERAL. If an Event of Default has occurred and is
continuing, the Collateral Agent may exercise, in addition to all other rights
and remedies granted to it in this Agreement and in any other instrument or
agreement securing, evidencing or relating to the Obligations, all rights and
remedies of a secured party under the Code. Without limiting the generality of
the foregoing, if an Event of Default has occurred and is continuing, the
Collateral Agent, without demand of performance or other demand, presentment,
protest, advertisement or notice of any kind (except any notice required by law
referred to below or expressly provided for) to or upon the Grantor or any other
Person (all and each of which demands, defenses, advertisements and notices are,
to the extent permitted by applicable law, hereby waived), may in such
circumstances forthwith collect, receive, appropriate and realize upon the
Collateral, or any part thereof, and/or may forthwith sell, license, assign,
give option or options to purchase, or otherwise dispose of and deliver the
Collateral (other than funds held in the Collateral Account) or any part thereof
(or contract to do any of the foregoing), at public or

                                      -11-
<PAGE>

private sale or sales, at any exchange, broker's board or office of the
Collateral Agent or elsewhere upon such terms and conditions as it may deem
advisable and at such prices as it may deem best, for cash or on credit or for
future delivery without assumption of any credit risk. The Collateral Agent
shall have the right upon any such public sale or sales, and, to the extent
permitted by law, upon any such private sale or sales, to purchase the whole or
any part of the Collateral so sold, free of any right or equity of redemption in
the Grantor, which right or equity is hereby waived, to the extent permitted by
applicable law, or released.

            The Grantor further agrees that, if an Event of Default has occurred
and is continuing, at the Collateral Agent's request, to assemble the Collateral
(other than funds held in the Collateral Account) and make it available to the
Collateral Agent at places which the Collateral Agent shall reasonably select,
whether at the Grantor's premises or elsewhere. The Collateral Agent shall apply
the net proceeds of any such collection, recovery, receipt, appropriation,
realization or sale, after deducting all reasonable costs and expenses of every
kind incurred therein or incidental to the care or safekeeping of any of the
Collateral or in any way relating to the Collateral or the rights of the
Collateral Agent hereunder, including, without limitation, reasonable attorneys'
fees and disbursements, to the payment in whole or in part of the Obligations,
in such order as the Collateral Agent may elect, and only after such application
and after the payment by the Collateral Agent of any other amount required by
any provision of law, need the Collateral Agent account for the surplus, if any,
to the Grantor. To the extent permitted by applicable law, the Grantor waives
all claims, damages and demands it may acquire against the Collateral Agent
arising out of the exercise by it of any rights hereunder, provided, that
nothing contained in this Section 8 shall relieve the Collateral Agent from
liability arising solely from its gross negligence or willful misconduct. If any
notice of a proposed sale or other disposition of Collateral shall be required
by law, such notice shall be deemed reasonable and proper if given at least ten
days before such sale or other disposition. The Grantor shall remain liable for
any deficiency if the proceeds of any sale or other disposition of the
Collateral are insufficient to pay the Obligations and the fees and
disbursements of any attorneys employed by the Collateral Agent to collect such
deficiency.

            9. LIMITATION ON DUTIES REGARDING PRESERVATION OF COLLATERAL. The
Collateral Agent's sole duty with respect to the custody, safekeeping and
physical preservation of the Collateral in its possession, under the Code or
otherwise, shall be to deal with it in the same manner as the Collateral Agent
deals with similar property for its own account. Neither the Collateral Agent
nor any of its directors, officers, employees or agents shall be liable for
failure to demand, collect or realize upon all or any part of the Collateral or
for any delay in doing so or shall be under any obligation to sell or otherwise
dispose of any Collateral upon the request of the Grantor or otherwise.

                                      -12-
<PAGE>

            10. POWERS COUPLED WITH AN INTEREST. All authorizations and agencies
herein contained with respect to the Collateral are irrevocable and powers
coupled with an interest until the Grantor has paid and performed in full all of
its obligations under the Transaction Documents.

            11. SEVERABILITY. Any provision of this Agreement which is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

            12. PARAGRAPH HEADINGS, CAPTIONS, ETC. The paragraph headings, the
captions and the footers used in this Agreement are for convenience of reference
only and are not to affect the construction hereof or be taken into
consideration in the interpretation hereof.

            13. NO WAIVER; CUMULATIVE REMEDIES. The Collateral Agent shall not
by any act, delay, indulgence, omission or otherwise be deemed to have waived
any right or remedy hereunder or to have acquiesced in any Event of Default or
in any breach of any of the terms and conditions hereof. No failure to exercise,
nor any delay in exercising, on the part of the Collateral Agent, any right,
power or privilege hereunder shall operate as a waiver thereof. No single or
partial exercise of any right, power or privilege hereunder shall preclude any
other or further exercise thereof or the exercise of any other right, power or
privilege. A waiver by the Collateral Agent of any right or remedy hereunder on
any one occasion shall not be construed as a bar to any right or remedy which
the Collateral Agent would otherwise have on any future occasion. The rights and
remedies herein and in the Notes and the other Transaction Documents are
cumulative, may be exercised singly or concurrently and are not exclusive of any
rights or remedies provided by law or in equity or by statute.

            14. WAIVERS AND AMENDMENTS; SUCCESSORS AND ASSIGNS. None of the
terms or provisions of this Agreement may be waived, amended, supplemented or
otherwise modified except by a written instrument executed by the party to be
charged with enforcement; provided, however, that any provision of this
Agreement may be waived, amended, supplemented or otherwise modified by the
Collateral Agent only with the prior written approval of the Majority Holders.
This Agreement shall be binding upon the successors and permitted assigns of the
Grantor and shall inure to the benefit of the Collateral Agent and its
successors and assigns. The Grantor may not assign its rights or obligations
under this Agreement without the prior written consent of the Collateral Agent,
which the Collateral Agent may withhold in the sole discretion of the Majority
Holders. The requirements for resignation, and appointment of a successor to,
the Collateral Agent are established by SCHEDULE II hereto and not by this
Agreement.

                                      -13-
<PAGE>

            15. TERMINATION OF SECURITY INTEREST; RELEASE OF COLLATERAL.

            (a) Upon the payment in full of all principal of and premium, if
any, and interest on the Notes and the payment in full of all other amounts for
Obligations that are due and payable at such time, and if no claims for payment
by the Company of any Obligations are at the time pending, the Security Interest
shall terminate and all rights to the Collateral shall revert to the Grantor.

            (b) The Security Interest shall terminate and the Collateral Agent
shall release funds from the Collateral Account upon the request of the Grantor
if all the following conditions precedent are satisfied:

            (1) no Event of Default and no event, which, with notice or passage
      of time, or both, would become an Event of Default has occurred and is
      continuing;

            (2) no Repurchase Event has occurred with respect to which any
      Holder has the right to exercise repurchase rights pursuant to Section 5
      of its Note or with respect to which any Holder has exercised such
      repurchase rights and the Repurchase Price has not been paid to such
      Holder or deposited in accordance with Section 7(k) of such Holder's Note
      and no event which, with notice or passage of time, or both, would become
      a Repurchase Event has occurred and is continuing;

            (3) the Registration Statement shall be effective and available for
      use by the Holders for the resale of the shares of Common Stock issued and
      issuable upon conversion of the Notes and issued or issuable upon exercise
      of the Warrants, the Redemption Warrants and the Other Redemption
      Warrants, as the case may be, and is reasonably expected to remain
      effective and available for such use for at least 30 days thereafter, and
      the Grantor shall be in compliance in all material respects with its
      obligations under the Registration Rights Agreements;

            (4) all amounts due and payable by the Grantor pursuant to Section
      17 have been paid;

            (5) No Maximum Share Amount Deficiency Exists under any Purchase
      Agreement;

            (6) the Earnings Release Condition shall have been satisfied and the
      Holders and the Grantor shall have given the Collateral Agent and the
      Holders the Release Certificate relating thereto; and

                                      -14-
<PAGE>

            (7) during the ten Business Days after the Grantor shall have given
      the Release Certificate to the Collateral Agent and the Holders, no Holder
      shall have notified the Collateral Agent that it objects to such release
      based on a failure to comply with this Section 15(b), which notice shall
      set forth a brief statement of the basis for such objection.

            (c) In case at any time the amount in the Collateral Account that
has not previously been released pursuant to this Section 15 shall exceed 50
percent of the aggregate outstanding principal amount of the Notes at such time,
the Grantor shall be entitled to request release of funds held in the Collateral
Account if all of the following conditions precedent are satisfied:

            (1) no Event of Default and no event, which, with notice or passage
      of time, or both, would become an Event of Default has occurred and is
      continuing;

            (2) no Repurchase Event has occurred with respect to which any
      Holder has the right to exercise repurchase rights pursuant to Section 5
      of its Note or with respect to which any Holder has exercised such
      repurchase rights and the Repurchase Price has not been paid to such
      Holder or deposited in accordance with Section 7(k) of such Holder's Note
      and no event which, with notice or passage of time, or both, would become
      a Repurchase Event has occurred and is continuing;

            (3) the Registration Statement shall be effective and available for
      use by the Holders for the resale of the shares of Common Stock issued and
      issuable upon conversion of the Notes and issued or issuable upon exercise
      of the Warrants, the Redemption Warrants and the Other Redemption
      Warrants, as the case may be, and is reasonably expected to remain
      effective and available for such use for at least 30 days thereafter, and
      the Grantor shall be in compliance in all material respects with its
      obligations under the Registration Rights Agreements;

            (4) all amounts due and payable by the Grantor pursuant to Section
      17 have been paid;

            (5) the Grantor shall have furnished a request to the Collateral
      Agent, with copies to each Holder, stating:

            (A) the aggregate outstanding principal amount of the Notes;

            (B) the amount by which the funds held in the Collateral Account
      exceed 50 percent of the aggregate outstanding principal amount of the
      Notes;

                                      -15-
<PAGE>

            (C) that the Grantor is requesting release of the amount stated in
      such request pursuant to the immediately preceding clause (B); and

            (D) that all of the requirements of this Section 15(c) for release
      of such Collateral, other than the requirements of Section 15(c)(7), have
      been satisfied;

            (6) no Maximum Share Amount Deficiency exists under any Purchase
      Agreement; and

            (7) during the ten Business Days after the Grantor shall have given
      the request specified in the immediately preceding clause (5) of this
      Section 15(c) to the Holder and the Collateral Agent, no Holder shall have
      notified the Collateral Agent that it objects to such release based on a
      failure to comply with this Section 15(c), which notice shall set forth a
      brief statement of the basis for such objection.

            (d) If an Event of Default shall have occurred and be continuing,
the Collateral Agent shall disburse the funds held by it pursuant to this
Agreement as follows:

            (i) First, to pay any amounts payable to the Collateral Agent
      pursuant to Section 17 that have not been paid by the Grantor;

            (ii) Second, to pay each Holder on a pro rata basis the amount of
      all accrued and unpaid interest (and interest, if any, thereon at the
      Default Rate) then due each Holder in accordance with the terms of their
      respective Notes through the most recent Interest Payment Date;

            (iii) Third, to pay each Holder on a pro rata basis the amount, if
      any, of unpaid principal then due on the Installment Maturity Date or
      Final Maturity Date, as the case may be, of any installment of principal
      of such Holder's Notes;

            (iv) Fourth, to pay each Holder, on a pro rata basis, the amount
      then due upon acceleration, if any, pursuant to Section 4 of such Holder's
      Note(s); and then

            (v) Fifth, to pay each Holder who has exercised its repurchase
      rights under Section 5 of the Notes, on a pro rata basis, all of the
      applicable unpaid Repurchase Price for each of the Notes or portions
      thereof required to be repurchased; and then

                                      -16-
<PAGE>

            (vi) Sixth, to pay each Holder any other amount due and payable to
      such Holder under the Transaction Documents; and then

            (vii) Seventh, the remaining amount, if any, to the Grantor.

provided, however, that if the amount of funds held by the Collateral Agent is
insufficient to pay all amounts due to the Holders pursuant to clauses (ii) and
(iv) above, then the amount paid to the Holders pursuant to this Section 15(d)
shall be prorated among the Holders in proportion to the respective amounts due
each Holder pursuant to the particular such clause or clauses for which such
funds are insufficient.

            (e) At any time and from time to time prior to termination of the
Security Interest pursuant to Section 15(a) or 15(b) or release of all
Collateral pursuant to Section 15(c), the Collateral Agent shall release any of
the Collateral only with the prior written consent of the Majority Holders.

            (f) Upon any such termination of the Security Interest or release of
all the Collateral, the Collateral Agent will, at the expense of the Grantor,
execute and deliver to the Grantor such documents and take such other actions as
the Grantor shall reasonably request to evidence the termination of the Security
Interest and deliver to the Grantor all Collateral so released then in its
possession.

            16. NOTICES. Any notices required or permitted to be given under the
terms of this Agreement shall be in writing and shall be sent by mail, personal
delivery, telephone line facsimile transmission or courier and shall be
effective five days after being placed in the mail, if mailed, or upon receipt,
if delivered personally, by telephone line facsimile transmission or by courier,
in each case addressed to a party at such party's address (or telephone line
facsimile transmission number) shown below or such other address (or telephone
line facsimile transmission number) as a party shall have provided by notice to
the other party in accordance with this provision. In the case of any notice to
the Grantor, such notice shall be addressed to the Grantor at 2711 N. Haskell
Avenue, Suite 2300, LB 36, Dallas, Texas 75204, Attention: Chief Financial
Officer (telephone line facsimile transmission number (214) 515-7385), and in
the case of any notice to the Collateral Agent, such notice shall be addressed
to the Collateral Agent at Law Offices of Brian W Pusch, as Collateral Agent,
Penthouse Suite, 29 West 57th Street, New York, New York (telephone line
facsimile number (212) 980-7055).

            17. FEES AND EXPENSES. The Grantor agrees to pay the fees of the
Collateral Agent in performing its services under this Agreement ($10,000 per
year, payable annually in advance, in the case of the initial Collateral Agent)
and all expenses (including but not limited to reasonable attorneys' fees and
costs for legal services, costs of insurance and payments of taxes or other
charges) of, or incidental

                                      -17-
<PAGE>

to, the custody, care, sale or realization on any of the Collateral or in any
way relating to the performance of the obligations or the enforcement or
protection of the rights of the Collateral Agent hereunder.

            18. CONCERNING COLLATERAL AGENT. The Grantor acknowledges that the
rights and responsibilities of the Collateral Agent under this Agreement with
respect to any action taken by the Collateral Agent or the exercise or
nonexercise by the Collateral Agent of any option, right, request, judgment or
other right or remedy provided for herein or resulting or arising out of this
Agreement shall, as between the Collateral Agent and the Holders, be governed by
SCHEDULE II hereto and by such other agreements with respect thereto as may
exist from time to time among them, but, as between the Collateral Agent and the
Grantor, except as expressly provided in Sections 14 and 15, the Collateral
Agent shall be conclusively presumed to be acting as agent for the Holders with
full and valid authority so to act or refrain from acting, and the Grantor shall
not be under any obligation to make any inquiry respecting such authority. The
Collateral Agent hereby waives for the benefit of the Holders any claim, right
or lien of the Collateral Agent against the Collateral arising under applicable
law or arising from any business or transaction between the Collateral Agent and
the Grantor other than pursuant to this Agreement or any of the other
Transaction Documents.

            19. SURVIVAL. All representations, warranties, covenants and
agreements of the Grantor and of the Collateral Agent contained herein will
survive the execution and delivery hereof and the release of any Collateral
pursuant hereto and shall remain operative and in full force and effect
regardless of any investigation made by or on behalf of the Collateral Agent or
the Grantor or any person who controls the Collateral Agent or the Grantor.

            20. GRANTOR'S OBLIGATIONS ABSOLUTE, ETC. The obligations of the
Grantor under this Agreement shall be absolute and unconditional and shall
remain in full force and effect without regard to, and shall not be released,
suspended, discharged, terminated or otherwise affected by, any circumstance or
occurrence whatsoever, including, without limitation: (a) any renewal,
extension, amendment or modification of or addition or supplement to or deletion
from any of the Transaction Documents or any other agreement or instrument
referred to therein, or any assignment or transfer of any thereof; (b) any
waiver, consent, extension, indulgence or other action or inaction under or in
respect of any such Transaction Document or other agreement or instrument; (c)
any furnishing of any additional security to the Collateral Agent or its
assignees or any acceptance thereof or any release of any security by the
Collateral Agent or its assignees; (d) any limitation on any party's liability
or obligations under any such Transaction Document or other agreement or
instrument or any invalidity or unenforceability, in whole or in part, of any
such Transaction Document or other agreement or instrument or any term thereof;
or (e) any bankruptcy, insolvency, reorganization, composition, adjustment,
dissolution, liquidation or other like proceeding relating to

                                      -18-
<PAGE>

the Grantor, or any action taken with respect to this Agreement by any trustee
or receiver, or by any court, in any such proceeding, whether or not the Grantor
shall have notice or knowledge of any of the foregoing.

            21. INTEGRATION. This Agreement represents the entire agreement of
the Grantor and the Collateral Agent with respect to the subject matter hereof,
and there are no promises, undertakings, representations or warranties by the
parties relative to the subject matter hereof not expressly set forth or
referred to herein or therein.

            22. GOVERNING LAW. This Agreement and the rights and obligations of
the Grantor under this Agreement shall be governed by, and construed and
interpreted in accordance with, the law of the State of New York, except to the
extent that under the New York Uniform Commercial Code the laws of another
jurisdiction govern matters of perfection and the effect of perfection or
non-perfection of any security interest granted hereunder.

            23. COUNTERPARTS; EXECUTION. This Agreement may be executed in any
number of counterparts and by the parties hereto on separate counterparts, but
all the counterparts taken together shall be deemed to constitute one and the
same instrument. This Agreement, once executed by a party, may be delivered to
the other party hereto by telephone line facsimile transmission of a copy of
this Agreement bearing the signature of the party so delivering this Agreement.

            24. ALTERNATIVE OR SUBSTITUTE ARRANGEMENTS. The Grantor may make a
proposal to the Holders to implement within six months after the date of this
Agreement the following:

            (a) As a substitute for this Agreement, establishment of an
      irrevocable standby letter of credit issued by a financial institution,
      acceptable to the Holders in their sole discretion, for the benefit of the
      Holders or their agent in an amount equal to $10,000,000.00 and providing
      for drawings thereunder in the circumstances in which the Collateral Agent
      is entitled by this Agreement to apply amounts in the Collateral Account
      to pay Obligations and otherwise on terms acceptable to the Holders in
      their sole discretion; or

            (b) Arrangements for the Collateral Agent to hold the amounts
      otherwise required by this Agreement to be held in the Collateral Account
      established hereunder in a collateral account maintained by the Collateral
      Agent at an institution, acceptable to the Holders in their sole
      discretion, other than Citibank, N.A., but nonetheless in the form of cash
      or cash equivalents.

                                      -19-
<PAGE>

The Holders shall be under no obligation to accept any such proposal from the
Grantor. The Holders shall, in good faith, consider any such proposal, but may
accept it or reject it in their sole discretion.

                            [Signature page follows]

                                      -20-
<PAGE>

            IN WITNESS WHEREOF, the Grantor and the Collateral Agent have caused
this Agreement to be duly executed and delivered by their respective officers or
other representatives thereunto duly authorized as of the date first above
written.

                                       ZIX CORPORATION

                                       By: /s/ Brad Almond
                                           -----------------------------------
                                           Name:  Brad Almond
                                           Title: CFO

                                       LAW OFFICES OF BRIAN W PUSCH,
                                           AS COLLATERAL AGENT

                                       By: /s/ Brian W. Pusch
                                         -------------------------------------
                                                 Brian W. Pusch

                                      -21-
<PAGE>

                                   SCHEDULE I

                  FILINGS REQUIRED TO PERFECT SECURITY INTEREST

1. Secretary of State of the State of Texas

2. Department of State of the State of New York

                                      I-1
<PAGE>

                                   SCHEDULE II

                              THE COLLATERAL AGENT

            1. APPOINTMENT. The Holders (all capitalized terms used in this
SCHEDULE II and not otherwise defined shall have the respective meanings
provided in the Security Agreement to which this SCHEDULE II is attached (the
"Agreement")), by their acceptance of the benefits of the Agreement, hereby
irrevocably designate Law Offices of Brian W Pusch, as Collateral Agent, to act
as specified herein and in the Agreement. Each Buyer hereby irrevocably
authorizes, and each other Holder of any Note by the acceptance of such Note
shall be deemed irrevocably to authorize, the Collateral Agent to take such
action on its behalf under the provisions of the Agreement and any other
instruments and agreements referred to herein or therein and to exercise such
powers and to perform such duties hereunder and thereunder as are specifically
delegated to or required of the Collateral Agent by the terms hereof and thereof
and such other powers as are reasonably incidental thereto. The Collateral Agent
may perform any of its duties hereunder by or through its agents or employees.

            2. NATURE OF DUTIES. The Collateral Agent shall have no duties or
responsibilities except those expressly set forth in the Agreement. Neither the
Collateral Agent nor any of its officers, directors, employees or agents shall
be liable for any action taken or omitted by it as such under the Agreement or
hereunder or in connection herewith or therewith, unless caused by its or their
gross negligence or willful misconduct. The duties of the Collateral Agent shall
be mechanical and administrative in nature; the Collateral Agent shall not have
by reason of the Agreement or any other Transaction Document a fiduciary
relationship in respect of any Holder; and nothing in the Agreement, expressed
or implied, is intended to or shall be so construed as to impose upon the
Collateral Agent any obligations in respect of the Agreement except as expressly
set forth herein. The Collateral Agent shall not take any material action or
exercise any material right or power pursuant to Section 6, 7 or 8 of this
Agreement without the authorization or direction of the Majority Holders;
provided, however, that if the Collateral Agent determines that it is unable to
contact the Majority Holders for purposes of seeking such authorization or
direction or time will not permit the Collateral Agent to so contact the
Majority Holders prior to such time as detriment may occur to the rights of the
Collateral Agent or the Holders from any failure of the Collateral Agent to act
or exercise such right, then in any such case the Collateral Agent may take such
action or exercise such right without specific authorization or direction from
the Majority Holders.

            The Collateral Agent shall not be liable for any act it may do or
omit to do while acting in good faith and in the exercise of its own best
judgment. Any act done or omitted by the Collateral Agent on the advice of its
own attorneys shall be deemed conclusively to have been done or omitted in good
faith. The Collateral Agent shall have the right at any time to consult with
counsel on any question

                                      II-1
<PAGE>

arising under the Agreement. The Collateral Agent shall incur no liability for
any delay reasonably required to obtain the advice of counsel.

            3. LACK OF RELIANCE ON THE COLLATERAL AGENT. Independently and
without reliance upon the Collateral Agent, each Holder, to the extent it deems
appropriate, has made and shall continue to make (i) its own independent
investigation of the financial condition and affairs of the Grantor and its
subsidiaries in connection with the making and the continuance of the
Obligations and the taking or not taking of any action in connection therewith,
and (ii) its own appraisal of the creditworthiness of the Grantor and its
subsidiaries, and the Collateral Agent shall have no duty or responsibility,
either initially or on a continuing basis, to provide any Holder with any credit
or other information with respect thereto, whether coming into its possession
before any Obligation arises or the purchase of any Note, or at any time or
times thereafter. The Collateral Agent shall not be responsible to any Holder
for any recitals, statements, information, representations or warranties herein
or in any document, certificate or other writing delivered in connection
herewith or for the execution, effectiveness, genuineness, validity,
enforceability, perfection, collectibility, priority or sufficiency of the
Agreement or the financial condition of the Grantor or be required to make any
inquiry concerning either the performance or observance of any of the terms,
provisions or conditions of the Agreement, or the financial condition of the
Grantor, or the existence or possible existence of any Event of Default.

            4. CERTAIN RIGHTS OF THE COLLATERAL AGENT. No Holder shall have the
right to cause the Collateral Agent to take any action with respect to the
Collateral, with only the Majority Holders having the right to direct the
Collateral Agent to take any such action. If the Collateral Agent shall request
instructions from the Majority Holders with respect to any act or action
(including failure to act) in connection with the Agreement, the Collateral
Agent shall be entitled to refrain from such act or taking such action unless
and until it shall have received instructions from the Majority Holders, and to
the extent requested, appropriate indemnification in respect of actions to be
taken by the Collateral Agent; and the Collateral Agent shall not incur
liability to any person by reason of so refraining. Without limiting the
foregoing, no Holder shall have any right of action whatsoever against the
Collateral Agent as a result of the Collateral Agent acting or refraining from
acting hereunder in accordance with the instructions of the Majority Holders or
as otherwise specifically provided in the Agreement.

            5. RELIANCE. The Collateral Agent shall be entitled to rely, and
shall be fully protected in relying, upon any note, writing, resolution, notice,
statement, certificate, telex, teletype or telecopier message, cablegram,
radiogram, order or other document or telephone message signed, sent or made by
the proper person or entity, and, with respect to all legal matters pertaining
to the Agreement and its duties thereunder, upon advice of counsel selected by
it.

                                      II-2
<PAGE>

            6. LIMITATION OF HOLDER LIABILITY. The Holders shall not be liable
for any liabilities, obligations, losses, damages, penalties, actions,
judgments, suits, costs, expenses or disbursements of any kind or nature
whatsoever which may be imposed on, incurred by or asserted against the
Collateral Agent in performing its duties hereunder or under the Agreement, or
in any way relating to or arising out of the Agreement.

            7. THE COLLATERAL AGENT IN ITS INDIVIDUAL CAPACITY. The Collateral
Agent and its affiliates may lend money to, purchase, sell and trade in
securities of and generally engage in any kind of business with the Grantor or
any affiliate or subsidiary of the Grantor as if it were not performing the
duties specified herein, otherwise without having to account for the same to the
Holders; provided, however, that the Collateral Agent on behalf of itself and
such affiliates, hereby waives any claim, right or lien against the Collateral
in any way arising from or relating to any such loan, securities transaction or
business with the Grantor. The Collateral Agent is legal counsel to one of the
initial Holders and may act as legal counsel for one or more other Holders in
the future. By its acceptance of a Note, each Holder waives any conflict of
interest that may arise from such representation.

            8. HOLDERS. The Collateral Agent may deem and treat the holder of
record of any Note as the owner thereof for all purposes hereof unless and until
a written notice of the assignment or transfer thereof, as the case may be,
shall have been filed with the Collateral Agent. Any request, authority or
consent of any person or entity who, at the time of making such request or
giving such authority or consent, is the holder of record of any Note shall be
conclusive and binding on any subsequent holder, transferee or assignee, as the
case may be, of such Note or of any Note(s) issued in exchange therefor.

            9. RESIGNATION BY THE COLLATERAL AGENT. (a) The Collateral Agent may
resign from the performance of all its functions and duties under the Agreement
at any time by giving 60 days' prior written notice (as provided in the
Agreement) to the Grantor and the Holders. Such resignation shall take effect
upon the appointment of a successor Collateral Agent pursuant to clauses (b) and
(c) below.

            (b) Upon any such notice of resignation, the Majority Holders shall
appoint a successor Collateral Agent hereunder.

            (c) If a successor Collateral Agent shall not have been so appointed
within said 60-day period, the Collateral Agent shall then appoint a successor
Collateral Agent who shall serve as Collateral Agent hereunder or thereunder
until such time, if any, as the Majority Holders appoint a successor Collateral
Agent as provided above. If a successor Collateral Agent has not been appointed
within such

                                      II-3
<PAGE>

60-day period, the Collateral Agent may petition any court of competent
jurisdiction or may interplead the Grantor and Holders in a proceeding for the
appointment of a successor Collateral Agent, and all fees, including but not
limited to extraordinary fees associated with the filing of interpleader, and
expenses associated therewith shall be payable by the Grantor.

            (d) The fees of any successor Collateral Agent for its services as
such shall be payable by the Grantor.

                                      II-4

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