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                                                                     EXHIBIT 2.3


                        FORM OF COMPANY VOTING AGREEMENT

        THIS COMPANY VOTING AGREEMENT (this "Agreement") is made and entered
into as of October 20, 1999, among Critical Path, Inc., a California corporation
("Parent"), and the undersigned shareholder (the "Shareholder") of ISOCOR, a
California corporation (the "Company").

                                    RECITALS

        A.     The Company, Merger Sub (as defined below) and Parent have
entered into an Agreement and Plan of Reorganization (the "Reorganization
Agreement"), which provides for the merger (the "Merger") of a wholly-owned
subsidiary of Parent ("Merger Sub") with and into the Company. Pursuant to the
Merger, all outstanding capital stock of the Company shall be converted into the
right to receive common stock of Parent, as provided by the Reorganization
Agreement;

        B.     Shareholder is the beneficial owner (as defined in Rule 13d-3
under the Securities Exchange Act of 1934, as amended (the "Exchange Act")) of
such number of shares of the outstanding capital stock of the Company and shares
subject to outstanding options and warrants as is indicated on the signature
page of this Agreement; and

        C.     In consideration of the execution of the Reorganization Agreement
by Parent, Shareholder (in his or her capacity as such) agrees to vote the
Shares (as defined below) and other such shares of capital stock of the Company
over which Shareholder has voting power so as to facilitate consummation of the
Merger.

        NOW, THEREFORE, intending to be legally bound, the parties hereto agree
as follows:

        1.     Certain Definitions. Capitalized terms not defined herein shall
have the meanings ascribed to them in the Reorganization Agreement. For purposes
of this Agreement:

               1.1    "Expiration Date" shall mean the earlier to occur of (i)
such date and time as the Reorganization Agreement shall have been terminated
pursuant to Article VII thereof or (ii) the Effective Time.

               1.2    "Person" shall mean any (i) individual, (ii) corporation,
limited liability company, partnership or other entity, or (iii) governmental
authority.

               1.3    "Shares" shall mean: (i) all securities of the Company
(including all shares of Company Common Stock and all options, warrants and
other rights to acquire shares of Company Common Stock) owned by Shareholder as
of the date of this Agreement; and (ii) all additional securities of the Company
(including all additional shares of Company Common Stock and all additional
options, warrants and other rights to acquire shares of Company Common Stock) of
which



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Shareholder acquires ownership during the period from the date of this Agreement
through the Expiration Date.

               1.4    Transfer. A Person shall be deemed to have effected a
"Transfer" of a security if such person directly or indirectly: (i) sells,
pledges, encumbers, grants an option with respect to, transfers or disposes of
such security or any interest in such security; or (ii) enters into an agreement
or commitment providing for the sale of, pledge of, encumbrance of, grant of an
option with respect to, transfer of or disposition of such security or any
interest therein.

        2.     Transfer of Shares.

               2.1    Transferee of Shares to be Bound by this Agreement.
Shareholder agrees that, during the period from the date of this Agreement
through the Expiration Date, Shareholder shall not cause or permit any Transfer
of any of the Shares to be effected unless such Transfer is in accordance with
any affiliate agreement between Shareholder and Parent contemplated by the
Reorganization Agreement and each Person to which any of such Shares, or any
interest in any of such Shares, is or may be transferred shall have: (a)
executed a counterpart of this Agreement and a proxy in the form attached hereto
as Exhibit A (with such modifications as Parent may reasonably request); and (b)
agreed in writing to hold such Shares (or interest in such Shares) subject to
all of the terms and provisions of this Agreement.

               2.2    Transfer of Voting Rights. Shareholder agrees that, during
the period from the date of this Agreement through the Expiration Date,
Shareholder shall not deposit (or permit the deposit of) any Shares in a voting
trust or grant any proxy or enter into any voting agreement or similar agreement
in contravention of the obligations of Shareholder under this Agreement with
respect to any of the Shares.

        3.     Agreement to Vote Shares. At every meeting of the shareholders of
the Company called, and at every adjournment thereof, and on every action or
approval by written consent of the shareholders of the Company, Shareholder (in
his or her capacity as such) shall cause the Shares to be voted in favor of
approval of the Reorganization Agreement, the related Agreement of Merger and
the Merger and in favor of any matter that could reasonably be expected to
facilitate the Merger. Furthermore, at every meeting of the shareholders of the
Company called, and at every adjournment thereof, and an every action or
approval by written consent of the shareholders of the Company, Shareholder (in
his or her capacity as such) shall cause the Shares to be voted against approval
of any other Acquisition Proposal (as defined in the Reorganization Agreement).

        4.     Irrevocable Proxy. Concurrently with the execution of this
Agreement, Shareholder agrees to deliver to Parent a proxy in the form attached
hereto as Exhibit A (the "Proxy"), which shall be irrevocable to the fullest
extent permissible by law, with respect to the Shares.

        5.     Representations and Warranties of the Shareholder.

               5.1    Shareholder (i) is the beneficial owner of the shares of
Company Common Stock and the options to purchase shares of Common Stock of the
Company indicated on the final


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page of this Agreement, free and clear of any liens, claims, options, rights of
first refusal, co-sale rights, charges or other encumbrances that would
adversely affect the ability of Shareholder to carry out its obligations
pursuant to this Agreement; (ii) does not beneficially own any securities of the
Company other than the shares of Company Common Stock and options and to
purchase shares of Common Stock of the Company indicated on the final page of
this Agreement; and (iii) has full power and authority to make, enter into and
carry out the terms of this Agreement and the Proxy.

               5.2    Shareholder has been advised that (i) the issuance of
shares of Parent Common Stock in connection with the Merger is expected to be
effected pursuant to a Registration Statement on Form S-4 under the Securities
Act of 1933, as amended (the "Act"), and as such will not be deemed "restricted
securities" within the meaning of Rule 144 promulgated thereunder (except as
discussed below) and resale of such shares will not be subject to any
restrictions other than as set forth in Rule 145 promulgated under the Act and
(ii) Shareholder may be deemed to be an affiliate of the Company. Shareholder
accordingly agrees not to sell, transfer or otherwise dispose of any Parent
Common Stock issued to Shareholder in the Merger unless (x) such sale, transfer
or other disposition is made in conformity with the requirements of Rule 145(d)
promulgated under the Act pursuant to an effective registration statement under
the Act or pursuant to an exemption from the registration requirements of such
Act, (y) an authorized representative of the SEC takes the position in writing
to the effect that the SEC would take no action, or that the staff of the SEC
would not recommend that the SEC take action, with respect to such sale,
transfer or other disposition, and a copy of such written position ("No Action
Correspondence") is delivered to Parent, or (z) Shareholder delivers to Parent a
written opinion of counsel, reasonably acceptable to Parent in form and
substance, that such sale, transfer or other disposition is otherwise exempt
from registration under the Act. Notwithstanding the foregoing, in the event
Shareholder is an affiliate of the Parent, any shares of Parent Common Stock
held by Shareholder will be subject to restrictions pursuant to Rule 144
promulgated under the Act.

               5.3    Shareholder has been advised that Parent will give stop
transfer instructions to its transfer agent with respect to any Parent Common
Stock received by Shareholder pursuant to the Merger and there will be placed on
the certificates representing such Parent Common Stock, or any substitutions
therefor, a legend stating in substance:

        "THE SHARES REPRESENTED BY THIS CERTIFICATE WERE ISSUED IN A TRANSACTION
        TO WHICH RULE 145 PROMULGATED UNDER THE SECURITIES ACT OF 1933, AS
        AMENDED, APPLIES AND MAY ONLY BE TRANSFERRED (A) IN CONFORMITY WITH RULE
        145(d) UNDER SUCH ACT, (B) IN ACCORDANCE WITH A WRITTEN OPINION OF
        COUNSEL, REASONABLY ACCEPTABLE TO THE ISSUER IN FORM AND SUBSTANCE THAT
        SUCH TRANSFER IS EXEMPT FROM REGISTRATION UNDER THE SECURITIES ACT OF
        1933, AS AMENDED OR (C) PURSUANT TO AN EFFECTIVE REGISTRATION UNDER SUCH
        ACT."

        The legend set forth above shall be removed (by delivery of a substitute
certificate without such legend) and Parent shall instruct its transfer agent to
remove such legend, if Shareholder


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delivers to Parent (i) satisfactory written evidence that the shares have been
sold in compliance with Rule 145 (in which case, the substitute certificate will
be issued in the name of the transferee), (ii) a copy of the No Action
Correspondence, (iii) an opinion of counsel, in form and substance reasonably
satisfactory to Parent to the effect that public sale of the shares by the
holder thereof is no longer subject to Rule 145, or (iv) a written request for
removal of such legend after the earlier of (x) the inapplicability of Rule 145
by its terms, (y) the effective date of any action by the SEC eliminating the
restrictions upon sale, transfer or disposition under Rule 145 or otherwise
rendering compliance with such restrictions unnecessary, or (z) the effective
date an effective registration statement relating to such shares.

        6.     Additional Documents. Shareholder (in his or her capacity as
such) hereby covenants and agrees to execute and deliver any additional
documents necessary or desirable, in the reasonable opinion of Parent, to carry
out the intent of this Agreement.

        7.     Legending of Shares. If so requested by Parent, Shareholder
agrees that the Shares shall bear a legend stating that they are subject to this
Agreement and to an irrevocable proxy. Subject to the terms of Section 2 hereof,
Shareholder agrees that Shareholder shall not Transfer the Shares without first
having the aforementioned legend affixed to the certificates representing the
Shares.

        8.     Termination. This Agreement shall terminate and shall have no
further force or effect as of the Expiration Date.

        9.     Miscellaneous.

               9.1    Severability. If any term, provision, covenant or
restriction of this Agreement is held by a court of competent jurisdiction to be
invalid, void or unenforceable, then the remainder of the terms, provisions,
covenants and restrictions of this Agreement shall remain in full force and
effect and shall in no way be affected, impaired or invalidated.

               9.2    Binding Effect and Assignment. This Agreement shall be
binding upon and inure to the benefit of the parties hereto and their respective
successors and permitted assigns, but, except as otherwise specifically provided
herein, neither this Agreement nor any of the rights, interests or obligations
of the parties hereto may be assigned by either of the parties without prior
written consent of the other. Nothing contained in this Agreement, express or
implied, is intended to confer upon any person other than the parties hereto and
their respective successors and permitted assigns any rights or remedies of any
nature whatsoever by reason of this Agreement.

               9.3    Amendments and Modification. This Agreement may not be
modified, amended, altered or supplemented except upon the execution and
delivery of a written agreement executed by the parties hereto.

               9.4    Specific Performance; Injunctive Relief. The parties
hereto acknowledge that Parent shall be irreparably harmed and that there shall
be no adequate remedy at law for a violation of any of the covenants or
agreements of Shareholder set forth herein. Therefore, it is agreed that, in


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addition to any other remedies that may be available to Parent upon any such
violation, Parent shall have the right to enforce such covenants and agreements
by specific performance, injunctive relief or by any other means available to
Parent at law or in equity.

               9.5    Notices. All notices and other communications pursuant to
this Agreement shall be in writing and deemed to be sufficient if contained in a
written instrument and shall be deemed given if delivered personally,
telecopied, sent by nationally-recognized overnight courier or mailed by
registered or certified mail (return receipt requested), postage prepaid, to the
parties at the following address (or at such other address for a party as shall
be specified by like notice):

               if to Parent, to:

               Critical Path, Inc.
               320 First Street
               San Francisco, CA 94105
               Attention: Doug Hickey
                          Telephone No.: (415) 808-8800
                          Telecopy No.: (415) 808-8777

               with a copy to:

               Wilson Sonsini Goodrich & Rosati
               Professional Corporation
               650 Page Mill Road
               Palo Alto, California 94304-1050
               Attention: Alan K. Austin
                          Telephone No.: (650) 493-9300
                          Telecopy No.: (650) 493-6811

               if to Shareholder: to the address for notice set forth on the
                                  signature page hereof.


               9.6    Governing Law. This Agreement shall be governed by the
laws of the State of California, without reference to rules of conflicts of law.

               9.7    Entire Agreement. This Agreement and the Proxy contain the
entire understanding of the parties in respect of the subject matter hereof, and
supersede all prior negotiations and understandings between the parties with
respect to such subject matter.

               9.8    Effect of Headings. The section headings are for
convenience only and shall not affect the construction or interpretation of this
Agreement.

               9.9    Counterparts. This Agreement may be executed in several
counterparts, each of which shall be an original, but all of which together
shall constitute one and the same agreement.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


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        IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed on the day and year first above written.



CRITICAL PATH, INC.                                SHAREHOLDER


By: ____________________________________     By: _______________________________
    Signature of Authorized Signatory            Signature

Name: __________________________________     Name: _____________________________

Title: _________________________________     Title: ____________________________

                                             ___________________________________

                                             ___________________________________
                                             Print Address

                                             ___________________________________
                                             Telephone

                                             ___________________________________
                                             Facsimile No.

                                             Share beneficially owned:

                                             ________ shares of Company Common
                                             Stock

                                             ________ shares of Company Common
                                             Stock issuable upon exercise of
                                             outstanding options or warrants





                      [SIGNATURE PAGE TO VOTING AGREEMENT]



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                                IRREVOCABLE PROXY

        The undersigned shareholder of ISOCOR, a California corporation (the
"Company"), hereby irrevocably (to the fullest extent permitted by law) appoints
the directors on the Board of Directors of Critical Path, Inc., a California
corporation ("Parent"), and each of them, as the sole and exclusive attorneys
and proxies of the undersigned, with full power of substitution and
resubstitution, to vote and exercise all voting and related rights (to the full
extent that the undersigned is entitled to do so) with respect to all of the
shares of capital stock of the Company that now are or hereafter may be
beneficially owned by the undersigned, and any and all other shares or
securities of the Company issued or issuable in respect thereof on or after the
date hereof (collectively, the "Shares") in accordance with the terms of this
Proxy. The Shares beneficially owned by the undersigned shareholder of the
Company as of the date of this Proxy are listed on the final page of this Proxy.
Upon the undersigned's execution of this Proxy, any and all prior proxies given
by the undersigned with respect to any Shares are hereby revoked and the
undersigned agrees not to grant any subsequent proxies with respect to the
Shares until after the Expiration Date (as defined below).

        This Proxy is irrevocable (to the fullest extent permitted by law), is
coupled with an interest and is granted pursuant to that certain Company Voting
Agreement of even date herewith by and among Parent and the undersigned
shareholder (the "Voting Agreement"), and is granted in consideration of Parent
entering into that certain Agreement and Plan of Reorganization (the
"Reorganization Agreement"), among Parent, Initialize Acquisition Corp., a
California corporation and a wholly-owned subsidiary of Parent ("Merger Sub"),
and the Company. The Reorganization Agreement provides for the merger of Merger
Sub with and into the Company in accordance with its terms (the "Merger"). As
used herein, the term "Expiration Date" shall mean the earlier to occur of (i)
such date and time as the Reorganization Agreement shall have been validly
terminated pursuant to Article VII thereof or (ii) such date and time as the
Merger shall become effective in accordance with the terms and provisions of the
Reorganization Agreement.

        The attorneys and proxies named above, and each of them, are hereby
authorized and empowered by the undersigned, at any time prior to the Expiration
Date, to act as the undersigned's attorney and proxy to vote the Shares, and to
exercise all voting, consent and similar rights of the undersigned with respect
to the Shares (including, without limitation, the power to execute and deliver
written consents) at every annual, special or adjourned meeting of shareholders
of the Company and in every written consent in lieu of such meeting in favor of
approval of the Merger, the execution and delivery by the Company of the
Reorganization Agreement and the adoption and approval of the terms thereof and
in favor of each of the other actions contemplated by the Reorganization
Agreement and any action required in furtherance hereof and thereof.

        The attorneys and proxies named above may not exercise this Proxy on any
other matter except as provided above. The undersigned shareholder may vote the
Shares on all other matters.

        Any obligation of the undersigned hereunder shall be binding upon the
successors and assigns of the undersigned.



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        This Proxy is irrevocable (to the fullest extent permitted by law). This
Proxy shall terminate, and be of no further force and effect, automatically upon
the Expiration Date.


Dated: ________________, 1999


                       Signature of Shareholder: _______________________________

                       Print Name of Shareholder: ______________________________

                       Shares beneficially owned:

                              ________ shares of the Company Common Stock

                              ________ shares of the Company Common Stock
                              issuable upon exercise of outstanding options or
                              warrants
















                      [SIGNATURE PAGE TO IRREVOCABLE PROXY]