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                                                                     EXHIBIT 2.2

                                                                [CONFORMED COPY]


                             STOCK OPTION AGREEMENT


        THIS STOCK OPTION AGREEMENT (this "Agreement") is made and entered into
as of October 20, 1999, among Critical Path, Inc., a California corporation
("Parent"), and ISOCOR, a California corporation (the "Company"). Capitalized
terms used but not otherwise defined herein will have the meanings ascribed to
them in the Reorganization Agreement (as defined below).

                                    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 will be converted into the
right to receive Common Stock of Parent as provided by the Reorganization
Agreement.

        B.     As a condition to Parent's willingness to enter into the
Reorganization Agreement, Parent has requested that Company agree, and Company
has so agreed, to grant to Parent an option to acquire shares of the Company's
Common Stock, no par value (the "Company Shares"), upon the terms and subject to
the conditions set forth herein.

        NOW, THEREFORE, in consideration of the foregoing and of the mutual
covenants and agreements set forth herein and in the Reorganization Agreement
and for other good and valuable consideration, the receipt and adequacy of which
are hereby acknowledged, the parties hereto agree as follows:

        1. Grant of Option. The Company hereby grants to Parent an irrevocable
option (the "Option") to purchase from the Company up to a number of Company
Shares equal to 19.9% of the issued and outstanding Company Shares (the "Option
Shares") as of the first date, if any, upon which an Exercise Event (as defined
in Section 2(a) below) occurs, in the manner set forth below by paying cash to
the Company at a price of $23.54 per Company Share (the "Exercise Price"). In no
event shall the aggregate number of Option Shares exceed 19.9% of the Company
Shares issued and outstanding at the time of exercise of the Option.

        2. Exercise of Option.

        (a) The Option may be exercised by Parent, in whole or in part, at any
time or from time to time if the Reorganization Agreement is terminated pursuant
to Section 7.1(b), 7.1(d), 7.1(g), or 7.1(h) thereof and an event causing the
Termination Fee to become payable pursuant to Section 7.3(b) of the
Reorganization Agreement occurs (any of the events being referred to herein as
an "Exercise Event"). In the event Parent wishes to exercise the Option, Parent
will deliver to the Company a written notice (each an "Exercise Notice")
specifying the total number of Option Shares


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it wishes to acquire. Each closing of a purchase of Option Shares (a "Closing")
will occur on a date and at a time prior to the termination of the Option
designated by Parent in an Exercise Notice delivered at least two (2) business
days prior to the date of such Closing, which Closing will be held at the
principal offices of the Company.

               (b) The Option and this Agreement will terminate upon the
earliest of (i) the Effective Time, (ii) twelve (12) months following the date
on which the Reorganization Agreement is terminated pursuant to Section 7.1(g)
or 7.1(h) thereof, other than a termination pursuant to Section 7.1(h) as a
result of which no Termination Fee becomes payable pursuant to the proviso in
Section 7.3(b)(ii), and (iii) in the event the Reorganization Agreement has been
terminated pursuant to Section 7.1(b) or 7.1(d) thereof and the Termination Fee
became payable pursuant to Section 7.3(b)(iii) thereof, six (6) months after
payment of the Termination Fee; provided, however, that if the Option cannot be
exercised by reason of any applicable government order or because the waiting
period related to the issuance of the Option Shares under the HSR Act will not
have expired or been terminated, then the Option will not terminate until the
tenth business day after such impediment to exercise will have been removed or
will have become final and not subject to appeal. In the event that the Option
and this Agreement terminate as provided herein, this Agreement shall be of no
further force or effect.

        3. Conditions to Closing. The obligation of the Company to issue Option
Shares to Parent hereunder is subject to the conditions that (A) any waiting
period under the HSR Act applicable to the issuance of the Option Shares
hereunder will have expired or been terminated; (B) all material consents,
approvals, orders or authorizations of, or registrations, declarations or
filings with, any Federal, state or local administrative agency or commission or
other Federal state or local governmental authority or instrumentality, if any,
required in connection with the issuance of the Option Shares hereunder will
have been obtained or made, as the case may be; and (C) no preliminary or
permanent injunction or other order by any court of competent jurisdiction or
other Governmental Entity prohibiting or otherwise restraining such issuance
will be in effect. It is understood and agreed that at any time during which the
Option is exercisable, the parties will use their respective commercially
reasonable efforts to satisfy all conditions to Closing, so that a Closing may
take place as promptly as practicable.

        4. Closing. At any Closing, (A) the Company will deliver to Parent a
single certificate in definitive form representing the number of Company Shares
designated by Parent in its Exercise Notice, such certificate to be registered
in the name of Parent and to bear the restrictive legend set forth in Section 9
hereof, against delivery of (B) payment by Parent to the Company of the
aggregate purchase price for the Company Shares so designated and being
purchased by wire transfer of immediately available funds to an account
designated by the Company.

        5. Representations and Warranties of the Company. Company represents and
warrants to Parent that (A) Company is a corporation duly incorporated, validly
existing and in good standing under the laws of the State of California and has
the corporate power and authority to enter into this Agreement and to carry out
its obligations hereunder; (B) the execution and delivery of this Agreement by
the Company and consummation by the Company of the transactions contemplated
hereby have been duly authorized by all necessary corporate action on the part
of the Company and no other corporate proceedings on the part of the Company are
necessary to authorize this



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Agreement or any of the transactions contemplated hereby; (C) this Agreement has
been duly executed and delivered by the Company and constitutes a legal, valid
and binding obligation of the Company and, assuming this Agreement constitutes a
legal, valid and binding obligation of Parent, is enforceable against the
Company in accordance with its terms, except as may be limited by bankruptcy,
insolvency, reorganization or other similar laws affecting the enforcement of
creditors' rights generally and by general equitable principles; (D) except for
any filings required under the HSR Act, the Company has taken all necessary
corporate and other action to authorize and reserve for issuance and to permit
it to issue upon exercise of the Option, and at all times from the date hereof
until the termination of the Option will have reserved for issuance, a
sufficient number of unissued Company Shares for Parent to exercise the Option
in full and will take all necessary corporate or other action to authorize and
reserve for issuance all additional Company Shares or other securities which may
be issuable pursuant to Section 8(a) upon exercise of the Option, all of which,
upon their issuance and delivery in accordance with the terms of this Agreement,
will be validly issued, fully paid and nonassessable; (E) upon delivery of the
Company Shares and any other securities to Parent upon exercise of the Option,
Parent will acquire such Company Shares or other securities free and clear of
all material claims, liens, charges, encumbrances and security interests of any
kind or nature whatsoever, excluding those imposed by Parent; (F) the execution
and delivery of this Agreement by the Company do not, and the performance of
this Agreement by the Company will not, (i) conflict with or violate the
Articles of Incorporation or Bylaws of the Company, (ii) conflict with or
violate any law, rule, regulation, order, judgment or decree applicable to the
Company or by which its properties is bound or affected or (iii) result in any
breach of or constitute a default (or an event that with notice or lapse of time
or both would become a default) under, or impair the Company's rights or alter
the rights or obligations of any third party under, or give to others any rights
of termination, amendment, acceleration or cancellation of, or result in the
creation of a lien or encumbrance on any of the properties or assets of the
Company pursuant to, any material note, bond, mortgage, indenture, contract,
agreement, lease, license, permit, franchise or other instrument or obligation
to which the Company is a party or by which the Company or its respective
properties are bound or affected, except, with respect to clauses (ii) and
(iii), for any such conflicts, violations, breaches, defaults or other
occurrences that would not, individually and in the aggregate, have a Material
Adverse Effect; and (G) the execution and delivery of this Agreement by the
Company does not, and the performance of this Agreement by the Company will not,
require any consent, approval, authorization or permit of, or filing with, or
notification to, any Governmental Entity except pursuant to the HSR Act or
except as provided in clauses (A) or (B) of Section 2.5(b) of the Reorganization
Agreement.

        6. Certain Rights.

               (a) Parent Put. At the request of and upon notice by Parent (the
"Put Notice"), at any time during the period during which the Option is
exercisable pursuant to Section 2 (the "Purchase Period"), the Company (or any
successor entity thereof) will purchase from Parent the Option, to the extent
not previously exercised, at the price set forth in subparagraph (i) below (as
limited by subparagraph (iii) below), and the Option Shares, if any, acquired by
Parent pursuant thereto, at the price set forth in subparagraph (ii) below (as
limited by subparagraph (iii) below):

                      (i)    The difference between the "Market/Tender Offer
Price" for the Company Shares as of the date Parent gives notice of its intent
to exercise its rights under this



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Section 6(a) (which "Market/Tender Offer Price" shall mean the higher of (A) the
highest price per share offered as of such date pursuant to any Acquisition
Proposal which was made prior to such date and (B) the average closing sale
price of Company Shares as reported on Nasdaq during the twenty (20) consecutive
trading days ending on the trading day immediately preceding such date) and the
Exercise Price, multiplied by the number of Company Shares purchasable pursuant
to the Option, but only if the Market/Tender Offer Price is greater than the
Exercise Price. For purposes of determining the highest price offered pursuant
to any Acquisition Proposal which involves consideration other than cash, the
value of such consideration will be equal to the higher of (x) if securities of
the same class of the proponent of such Acquisition Proposal as such
consideration are traded on any national securities exchange or by any
registered securities association, a value based on the closing sale price or
closing asked price for such securities on their principal trading market on
such date and (y) the value ascribed to such consideration by the proponent of
such Acquisition Proposal, or if no such value is ascribed, a value determined
in good faith by the Board of Directors of the Company.

                      (ii)   The Exercise Price paid by Parent for Company
Shares acquired pursuant to the Option plus the difference between the
Market/Tender Offer Price and such Exercise Price (but only if the Market/Tender
Offer Price is greater than the Exercise Price) multiplied by the number of
Company Shares so purchased (provided that Parent then has beneficial ownership
of such Company Shares).

                      (iii)  Notwithstanding subparagraphs (i) and (ii) above,
with respect to payments pursuant to this Section 6(a), Company will not be
required to pay Parent in excess of an aggregate of $2,871,000.

               (b) Payment and Redelivery of Option or Shares. In the event
Parent exercises its rights under Section 6(a), the Company will, within five
(5) business days after Parent delivers a Put Notice pursuant to Section 6(a),
pay the required amount to Parent in immediately available funds and Parent will
surrender to the Company the certificates evidencing the Company Shares
purchased by Parent pursuant thereto and the Option shall be terminated.

        7. Registration Rights.

               (a) Following the termination of the Reorganization Agreement,
Parent (sometimes referred to herein as the "Holder") may by written notice (a
"Registration Notice") to the Company (the "Registrant") request the Registrant
to register under the Securities Act all or any part of the Option Shares
acquired by the Holder pursuant to this Agreement (such shares requested to be
registered, the "Registrable Securities") in order to permit the sale or other
disposition of any or all shares of the Registrable Securities that have been
acquired by or are issuable to Holder upon exercise of the Option in accordance
with the intended method of sale or other disposition stated by Holder,
including a "shelf" registration statement under Rule 415 under the Securities
Act or any successor provision. Holder agrees to cause, and to cause any
underwriters of any sale or other disposition to cause, any sale or other
disposition pursuant to such registration statement to be effected on a widely
distributed basis so that upon consummation thereof no purchaser or transferee
will, to the knowledge of Holder (after reasonable inquiry), own beneficially
more than 2.5% of the then-outstanding voting power of Registrant. Upon a
request for registration, the Registrant will



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have the option exercisable by written notice delivered to the Holder within ten
business days after the receipt of the Registration Notice, irrevocably to agree
to purchase all or any part of the Registrable Securities for cash at a price
(the "Option Price" equal to the product of (i) the number of Registrable
Securities so purchased and (ii) the per share average of the closing sale
prices of the Registrant's Common Stock on Nasdaq for the ten trading days
immediately preceding the date of the Registration Notice. Any such purchase of
Registrable Securities by the Registrant hereunder will take place at a closing
to be held at the principle executive offices of the Registrant or its counsel
at any reasonable date and time designated by the Registrant in such notice
within ten business days after delivery of such notice. The payment for the
shares to be purchased will be made by delivery at the time of such closing of
the Option Price in immediately available funds.

               (b) If the Registrant does not elect to exercise its option to
purchase pursuant to Section 7(a) with respect to all Registrable Securities,
the Registrant will use all reasonable efforts to effect, as promptly as
practicable, the registration under the Securities Act of the unpurchased
Registrable Securities requested to be registered in the Registration Notice and
to keep such registration statement effective for such period not in excess of
120 calendar days from the day such registration statement first becomes
effective as may be reasonably necessary to effect such sale or other
disposition; provided, however, that the Holder will not be entitled to more
than an aggregate of two effective registration statements hereunder. The
obligations of Registrant hereunder to file a registration statement and to
maintain its effectiveness may be suspended for up to 120 calendar days in the
aggregate if the Board of Directors of Registrant shall have determined that the
filing of such registration statement or the maintenance of its effectiveness
would require premature disclosure of material nonpublic information that would
materially and adversely affect Registrant or otherwise interfere with or
adversely affect any pending or proposed offering of securities of Registrant or
any other material transaction involving Registrant. If consummation of the sale
of any Registrable Securities pursuant to a registration hereunder does not
occur within 120 days after the filing with the SEC of the initial registration
statement therefor, the provisions of this Section 7 will again be applicable to
any proposed registration (subject to the proviso in the first sentence of this
Section 7(b)). The Registrant will use all commercially reasonable efforts to
cause any Registrable Securities registered pursuant to this Section 7 to be
qualified for sale under the securities or blue sky laws of such jurisdictions
as the Holder may reasonably request and will continue such registration or
qualification in effect in such jurisdictions; provided, however, that the
Registrant will not be required to qualify to do business in, or consent to
general service of process in, any jurisdiction by reason of this provision. If
Registrant effects a registration under the Securities Act of Company Common
Stock for its own account or for any other stockholders of Registrant (other
than on Form S-4 or Form S-8, or any successor form), it will allow Holder the
right to participate in such registration by selling its Registrable Securities,
and such participation will not affect the obligation of Registrant to effect
demand registration statements for Holder under this Section 7; provided that,
if the managing underwriters of such offering advise Registrant in writing that
in their opinion the number of shares of Company Common Stock requested to be
included in such registration exceeds the number which can be sold in such
offering, Registrant will include the shares requested to be included therein by
Holder pro rata with the shares intended to be included therein by Registrant.

               (c) The registration rights set forth in this Section 7 are
subject to the condition that the Holder will provide the Registrant with such
information with respect to the Holder's Registrable



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Securities, the plan for distribution thereof, and such other information with
respect to the Holder as, in the reasonable judgment of counsel for the
Registrant, is necessary to enable the Registrant to include in a registration
statement all facts required to be disclosed with respect to a registration
thereunder.

               (d) A registration effected under this Section 7 will be effected
at the Registrant's expense, except for underwriting discounts and commissions
and the fees and expenses of counsel to the Holder, and the Registrant will use
commercially reasonable efforts to provide to the underwriters such
documentation (including certificates, opinions of counsel and "comfort" letters
from auditors) as are customary in connection with underwritten public offerings
and as such underwriters may reasonably require. In connection with any
registration, the Holder and the Registrant agree to enter into an underwriting
agreement reasonably acceptable to each such party, in form and substance
customary for transactions of this type with the underwriters participating in
such offering.

               (e) Indemnification.

                      (i)    The Registrant will indemnify the Holder, each of
its directors and officers and each person who controls the Holder within the
meaning of Section 15 of the Securities Act, and each underwriter of the
Registrant's securities, with respect to any registration, qualification or
compliance which has been effected pursuant to this Agreement, against all
expenses, claims, losses, damages or liabilities (or actions in respect
thereof), including any of the foregoing incurred in settlement of any
litigation, commenced or threatened, arising out of or based on any untrue
statement (or alleged untrue statement) of a material fact contained in any
registration statement, prospectus, offering circular or other document, or any
amendment or supplement thereto, incident to any such registration,
qualification or compliance, or based on any omission (or alleged omission) to
state therein a material fact required to be stated therein or necessary to make
the statements therein, in light of the circumstances in which they were made,
not misleading, or any violation by the Registrant of any rule or regulation
promulgated under the Securities Act applicable to the Registrant in connection
with any such registration, qualification or compliance, and the Registrant will
reimburse the Holder and, each of its directors and officers and each person who
controls the Holder within the meaning of Section 15 of the Securities Act, and
each underwriter for any legal and any other expenses reasonably incurred in
connection with investigating, preparing or defending any such claim, loss,
damage, liability or action; provided, that the Registrant will not be liable in
any such case to the extent that any such claim, loss, damage, liability or
expense arises out of or is based on any untrue statement or omission or alleged
untrue statement or omission, made in reliance upon and in conformity with
written information furnished to the Registrant by such Holder or director or
officer or controlling person or underwriter seeking indemnification; provided,
however, that the indemnification provided for in this paragraph (i) of this
Section 7(e) shall not apply to amounts paid in settlement of any such loss,
claim, damage, liability or action if such settlement is effected without the
consent of the Registrant.

                      (ii)   The Holder will indemnify the Registrant, each of
its directors and officers and each underwriter of the Registrant's securities
covered by such registration statement and each person who controls the
Registrant within the meaning of Section 15 of the Securities Act, against all
expenses, claims, losses, damages and liabilities (or actions in respect
thereof), including



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any of the foregoing incurred in settlement of any litigation, commenced or
threatened, arising out of or based on any untrue statement (or alleged untrue
statement) of a material fact contained in any such registration statement,
prospectus, offering circular or other document, 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, or any violation by the
Holder of any rule or regulation promulgated under the Securities Act applicable
to the Holder in connection with any such registration, qualification or
compliance, and will reimburse the Registrant, such directors, officers or
control persons or underwriters for any legal or any other expenses reasonably
incurred in connection with investigating, preparing or defending any such
claim, loss, damage, liability or action, in each case to the extent, but only
to the extent, that such untrue statement (or alleged untrue statement) or
omission (or alleged omission) is made in such registration statement,
prospectus, offering circular or other document in reliance upon and in
conformity with written information furnished to the Registrant by the Holder
for use therein; provided, that in no event will any indemnity under this
Section 7(e) exceed the net proceeds of the offering received by the Holder, and
provided further, that the indemnification provided for in this paragraph (ii)
of this Section 7(e) shall not apply to amounts paid in settlement of any such
loss, claim, damage, liability or action if such settlement is effected without
the consent of the Holder.

                      (iii)  Each party entitled to indemnification under this
Section 7(e) (the "Indemnified Party") will give notice to the party required to
provide indemnification (the "Indemnifying Party") promptly after such
Indemnified Party has actual knowledge of any claim as to which indemnity may be
sought, and will permit the Indemnifying Party to assume the defense of any such
claim or any litigation resulting therefrom, provided, that counsel for the
Indemnifying Party, who will conduct the defense of such claim or litigation,
will be approved by the Indemnified Party (whose approval will not unreasonably
be withheld), and the Indemnified Party may participate in such defense at such
party's expense; provided, however, that the Indemnifying Party will pay such
expense if representation of the Indemnified Party by counsel retained by the
Indemnifying Party would be inappropriate due to actual or potential differing
interests between the Indemnified Party and any other party represented by such
counsel in such proceeding, and provided further, however, that the failure of
any Indemnified Party to give notice as provided herein will not relieve the
Indemnifying Party of its obligations under this Section 7(e) unless the failure
to give such notice is materially prejudicial to an Indemnifying Party's ability
to defend such action. No Indemnifying Party, in the defense of any such claim
or litigation will, except with the consent of each Indemnified Party, consent
to entry of any judgment or enter into any settlement which does not include as
an unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party of a release from all liability in respect to such claim or
litigation. No Indemnifying Party will be required to indemnify any Indemnified
Party with respect to any settlement entered into without such Indemnifying
Party's prior consent (which will not be unreasonably withheld).

        8. Adjustment Upon Changes in Capitalization; Rights Plans.

               (a) In the event of any change in the Company Shares by reason of
stock dividends, stock splits, reverse stock splits, mergers (other than the
Merger), recapitalizations, combinations, exchanges of shares and the like, the
type and number of shares or securities subject to the Option, the Exercise
Price will be adjusted appropriately, and proper provision will be made in the



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agreements governing such transaction so that Parent will receive, upon exercise
of the Option, the number and class of shares or other securities or property
that Parent would have received in respect of the Company Shares if the Option
had been exercised immediately prior to such event or the record date therefor,
as applicable.

               (b) At any time during which the Option is exercisable, and at
any time after the Option is exercised (in whole or in part, if at all), the
Company will not amend (nor permit the amendment of) any current shareholder
rights plan of the Company or its subsidiaries nor adopt (nor permit the
adoption of) a new stockholders rights plan that contains provisions for the
distribution or exercise of rights thereunder as a result of Parent or any
affiliate being the beneficial owner of shares of the Company by virtue of the
Option being exercisable or having been exercised (or as a result of
beneficially owning shares issuable in respect of any Option Shares).

        9. Restrictive Legends. Each certificate representing Option Shares
issued to Parent hereunder will include a legend in substantially the following
form:

        THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
        UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY BE REOFFERED OR
        SOLD ONLY IF SO REGISTERED OR IF AN EXEMPTION FROM SUCH REGISTRATION IS
        AVAILABLE. SUCH SECURITIES ARE ALSO SUBJECT TO ADDITIONAL RESTRICTIONS
        ON TRANSFER AS SET FORTH IN THE STOCK OPTION AGREEMENT DATED AS OF
        OCTOBER 20, 1999, A COPY OF WHICH MAY BE OBTAINED FROM THE ISSUER.

        It is understood and agreed that (i) the reference to restrictions
arising under the Securities Act in the above legend will be removed by delivery
of substitute certificate(s) without such reference if such Option Shares have
been registered pursuant to the Securities Act, such Option Shares have been
sold in reliance on and in accordance with Rule 144 under the Securities Act or
Holder has delivered to Registrant a copy of a letter from the staff of the SEC,
or an opinion of counsel in form and substance reasonably satisfactory to
Registrant and its counsel, to the effect that such legend is not required for
purposes of the Securities Act and (ii) the reference to restrictions pursuant
to this Agreement in the above legend will be removed by delivery of substitute
certificate(s) without such reference if the Option Shares evidenced by
certificate(s) containing such reference have been sold or transferred in
compliance with the provisions of this Agreement under circumstances that do not
require the retention of such reference.

        10. Listing and HSR Filing. The Company, upon the request of Parent,
will promptly file an application to list the Company Shares to be acquired upon
exercise of the Option for quotation on Nasdaq and will use its best efforts to
obtain approval of such listing as soon as practicable. Promptly after the date
hereof, each of the parties hereto will promptly file with the Federal Trade
Commission and the Antitrust Division of the United States Department of Justice
all required premerger notification and report forms and other documents and
exhibits required to be filed under the HSR Act to permit the acquisition of the
Company Shares subject to the Option at the earliest possible date.



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        11. Binding Effect. This Agreement will be binding upon and inure to the
benefit of the parties hereto and their respective successors and permitted
assigns. 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. Any shares sold by a party in compliance with the
provisions of Section 7 will, upon consummation of such sale, be free of the
restrictions imposed with respect to such shares by this Agreement and any
transferee of such shares will not be entitled to the rights of such party.
Certificates representing shares sold in a registered public offering pursuant
to Section 7 will not be required to bear the legend set forth in Section 9.

        12. Specific Performance. The parties hereto recognize and agree that if
for any reason any of the provisions of this Agreement are not performed in
accordance with their specific terms or are otherwise breached, immediate and
irreparable harm or injury would be caused for which money damages would not be
an adequate remedy. Accordingly, each party hereto agrees that in addition to
other remedies available, the other party hereto will be entitled to an
injunction restraining any violation or threatened violation of the provisions
of this Agreement or the right to enforce any of the covenants or agreements set
forth herein by specific performance. In the event that any action will be
brought in equity to enforce the provisions of this Agreement, neither party
hereto will allege, and each party hereto hereby waives the defense, that there
is an adequate remedy at law.

        13. Entire Agreement. This Agreement and the Reorganization Agreement
(including the exhibits thereto) constitute the entire agreement between the
parties hereto with respect to the subject matter hereof and supersede all other
prior agreements and understandings, both written and oral, between the parties
hereto with respect to the subject matter hereof.

        14. Further Assurances. Each party hereto will execute and deliver all
such further documents and instruments and take all such further action as may
be necessary in order to consummate the transactions contemplated hereby.

        15. Validity. The invalidity or unenforceability of any provision of
this Agreement will not affect the validity or enforceability of the other
provisions of this Agreement, which will remain in full force and effect. In the
event any Governmental Entity of competent jurisdiction holds any provision of
this Agreement to be null, void or unenforceable, the parties hereto will
negotiate in good faith and will execute and deliver an amendment to this
Agreement in order, as nearly as possible, to effectuate, to the extent
permitted by law, the intent of the parties hereto with respect to such
provision.

        16. Notices. All notices and other communications hereunder will be in
writing and will be deemed given if delivered personally or by commercial
delivery service, or sent via telecopy (receipt confirmed) to the parties at the
following addresses or telecopy numbers (or at such other address or telecopy
numbers for a party as will be specified by like notice):




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                      if to Parent, to:

                      Critical Path, Inc.
                      320 First Street
                      San Francisco, CA 94105
                      Attention: Doug Hickey, President & CEO
                                 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 Company, to:

                      ISOCOR
                      3420 Ocean Park Blvd.
                      Santa Monica, CA 90405
                      Attention: Paul Gigg, President & CEO
                                 Telephone No.: (310) 581-8100
                                 Telecopy No.: (310) 581-8111

                      with a copy to:

                      Venture Law Group
                      A Professional Corporation
                      2800 Sand Hill Road
                      Menlo Park, California 94025
                      Attention: Elias Blawie
                                 Telephone No.: (650) 854-4488
                                 Telecopy No.: (650) 854-1121

        17. Governing Law. This Agreement will be governed by and construed in
accordance with the laws of the State of California applicable to agreements
made and to be performed entirely within such State.

        18. Expenses. Except as otherwise expressly provided herein or in the
Reorganization Agreement, all costs and expenses incurred in connection with the
transactions contemplated by this Agreement will be paid by the party incurring
such expenses.



                                      -10-
   11

        19. Amendments; Waiver. This Agreement may be amended by the parties
hereto and the terms and conditions hereof may be waived only by an instrument
in writing signed on behalf of each of the parties hereto, or, in the case of a
waiver, by an instrument signed on behalf of the party waiving compliance.

        20. Assignment. Neither of the parties hereto may sell, transfer, assign
or otherwise dispose of any of its rights or obligations under this Agreement or
the Option created hereunder to any other person, without the express prior
written consent of the other party, except that the rights and obligations
hereunder will inure to the benefit of and be binding upon any successor of a
party hereto.

        21. Counterparts. This Agreement may be executed in counterparts, each
of which will be deemed to be an original, but both of which, taken together,
will constitute one and the same instrument.

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

        23. Defined Terms. Capitalized terms not defined herein shall have the
meanings ascribed to them in the Reorganization Agreement.



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                                      -11-
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        IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed by their respective duly authorized officers as of the date first above
written.



                                       CRITICAL PATH, INC.


                                       By: /s/ David Thatcher
                                           -------------------------------------
                                       Name: David Thatcher
                                       Title: Executive Vice President and Chief
                                              Financial Officer


                                       ISOCOR


                                       By: /s/ Paul Gigg
                                           -------------------------------------
                                       Name: Paul Gigg
                                       Title: President & CEO