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                                   DETACH HERE

                                      PROXY

                                     ISOCOR

                    PROXY FOR SPECIAL MEETING OF SHAREHOLDERS

           THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS



         The undersigned shareholder of ISOCOR, a California corporation, hereby
acknowledges receipt of the Notice of Special Meeting of Shareholders and Proxy
Statement, each dated December __, 1999, and hereby appoints __________________
and _________________, and each of them, proxies and attorneys-in-fact, with
full power to each of substitution and resubstitution, on behalf and in the name
of the undersigned, to represent the undersigned at the special meeting of
shareholders of ISOCOR to be held on Wednesday, January 19, 2000, at 10:00 a.m.,
local time, at ___________________________ California ________, and at any and
all continuation(s) or adjournment(s) thereof, and to vote all shares of Common
Stock which the undersigned would be entitled to vote, if then and there
personally present, on the matters set forth on the reverse side.

         Both of such attorneys or substitutes as shall be present and shall act
at said meeting or any and all continuation(s) or adjournment(s) thereof (or if
only one shall be present and acting, then that one) and shall have and may
exercise all the powers of said attorneys-in-fact hereunder.

THIS PROXY WILL BE VOTED AS DIRECTED, OR IF NO CONTRARY DIRECTION IS INDICATED,
WILL BE VOTED FOR ADOPTION OF THE AGREEMENT AND PLAN OF REORGANIZATION, DATED AS
OF OCTOBER 20, 1999, BY AND AMONG CRITICAL PATH, INC. ("CRITICAL PATH"),
INITIALIZE ACQUISITION CORP., A WHOLLY-OWNED SUBSIDIARY OF CRITICAL PATH, AND
ISOCOR, AND AS SAID PROXIES DEEM ADVISABLE ON SUCH OTHER MATTER(S) AS MAY
PROPERLY COME BEFORE THE MEETING.


                   CONTINUED AND TO BE SIGNED ON REVERSE SIDE

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SEE REVERSE                                                         SEE REVERSE
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ISOCOR
C/O [NAME AND ADDRESS
OF PROXY SOLICITOR]


                                   DETACH HERE


[X]   PLEASE MARK
      VOTES AS IN
      THIS EXAMPLE                                    FOR      AGAINST   ABSTAIN

1.    Proposal to adopt the Agreement and Plan of     [  ]      [  ]      [  ]
      Reorganization, dated as of October 20,
      1999, by and among Critical Path, Inc.
      ("Critical Path"), Initialize Acquisition
      Corp., a wholly-owned subsidiary of Critical
      Path, and ISOCOR

      In their discretion, the proxies are authorized to vote upon such other
      matter(s) which may properly come before the meeting or any and all
      continuation(s) or adjournment(s) thereof.

            MARK HERE FOR ADDRESS CHANGE AND NOTE AT LEFT [ ]
            This Proxy should be marked, dated and signed by the shareholder(s)
            exactly as his or her name appears hereon, and returned promptly in
            the enclosed envelope. Persons signing in a fiduciary capacity
            should so indicate. If a corporation, please sign in full corporate
            name by an authorized officer. If a partnership, please sign in
            partnership name by an authorized person. If shares are held by
            joint tenants or as community property, both should sign.


Date:____________                                Signature:____________________


Date:____________                                Signature:____________________


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