<PAGE>   1

        As filed with the Securities and Exchange Commission on January 24, 2000
                                                     Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                -----------------
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                -----------------

                               CRITICAL PATH, INC
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                -----------------

                                                 320 FIRST STREET
           CALIFORNIA                    SAN FRANCISCO, CALIFORNIA 94105
    ------------------------        ----------------------------------------
    (STATE OF INCORPORATION)        (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)

                          1992 ISOCOR STOCK OPTION PLAN
                    1996 ISOCOR DIRECTORS' STOCK OPTION PLAN
                          1999 ISOCOR STOCK OPTION PLAN
                            (FULL TITLE OF THE PLANS)

                                -----------------

                                DOUGLAS T. HICKEY
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                               CRITICAL PATH, INC.
                                 320 1ST STREET
                         SAN FRANCISCO, CALIFORNIA 94105
                                 (415) 808-8800
(NAME, ADDRESS, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)
                                -----------------
                                   Copies to:
                              Alan K. Austin, Esq.
                             Mark L. Reinstra, Esq.
                        Wilson Sonsini Goodrich & Rosati
                            Professional Corporation
                               650 Page Mill Road
                               Palo Alto, CA 94304
                                 (650) 493-9300
                                -----------------
                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
==========================================================================================================================
                                                       MAXIMUM      PROPOSED MAXIMUM   PROPOSED MAXIMUM
                                                    AMOUNT TO BE        OFFERING           AGGREGATE          AMOUNT OF
TITLE OF SECURITIES TO BE REGISTERED                REGISTERED(1)    PRICE PER SHARE    OFFERING PRICE    REGISTRATION FEE
------------------------------------------------   --------------   ----------------   ----------------   ----------------
<S>                                                <C>              <C>                 <C>               <C>
Common Stock, par value $0.001                     764,583 shares       $ 6.87(2)       $ 5,252,685.21        $1,386.71

     to be issued upon exercise of options
        granted under the 1992 ISOCOR Stock
        Option Plan...........................

     to be issued upon exercise of options
        granted under the 1996 ISOCOR Directors'    30,591 shares       $11.61(3)       $   355,161.51        $   93.76
        Stock Option Plan.....................

     to be issued upon exercise of options
        granted and outstanding and options        197,910 shares       $53.89(4)       $10,665,369.90        $2,815.66
        authorized and unissued under the 1999
        ISOCOR Stock Option Plan..............

             TOTAL............................     993,084 shares                       $15,996,697.20        $4,296.13
==========================================================================================================================
</TABLE>

(1) This Registration Statement shall also cover any additional shares of Common
    Stock which become issuable under the Plan being registered pursuant to this
    Registration Statement by reason of any stock dividend, stock split,
    recapitalization or any other similar transaction effected without the
    receipt of consideration which results in an increase in the number of the
    Registrant's outstanding shares of Common Stock.

(2) Computed in accordance with Rules 457(h) and 457(c) under the Securities Act
    of 1933. Such computation is based on the weighted average exercise price of
    $6.87 per share covering 764,583 outstanding options.

(3) Computed in accordance with Rules 457(h) and 457(c) under the Securities Act
    of 1933. Such computation is based on the weighted average exercise price of
    $11.61 per share covering 30,591 outstanding options.

(4) Computed in accordance with Rules 457(h) and 457(c) under the Securities Act
    of 1933. Such computation is based on the weighted average exercise price of
    $17.14 per share covering 56,700 outstanding options and the estimated
    exercise price of $68.63 per share covering 141,210 authorized but unissued
    shares. The estimated exercise price of $68.63 per share was computed in
    accordance with Rule 457 by averaging the high and low prices of a share of
    Critical Path, Inc. Common Stock as reported on the Nasdaq National Market
    on January 14, 2000.


<PAGE>   2

                               CRITICAL PATH, INC.

                       REGISTRATION STATEMENT ON FORM S-8

                                     PART II

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

     The following documents previously filed by Critical Path, Inc. (the
"Registrant") with the Securities and Exchange Commission (the "SEC") are hereby
incorporated by reference in this Registration Statement:

          (a) The Registrant's Quarterly Report on Form 10-Q for the fiscal
quarter ended September 30, 1999;

          (b) The Registrant's Quarterly Report on Form 10-Q for the fiscal
quarter ended June 30, 1999;

          (c) Prospectus of the Registrant, dated June 1, 1999;

          (d) The Registrant's Quarterly Report on Form 10-Q for the fiscal
quarter ended March 31, 1999;

          (e) The description of the Registrant's Common Stock contained in the
Registrant's Registration Statement on Form 8-A, dated February 1, 1999.

     All documents filed by the Registrant pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Securities Exchange Act of 1934, as amended, on or after the
date of this Registration Statement prior to the filing of a post-effective
amendment which indicates that all securities offered hereby have been sold or
which deregisters all securities then remaining unsold, shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of the filing of such documents.

     Any statement contained in this Registration Statement or in a document
incorporated by reference in this Registration Statement shall be deemed to be
modified or superseded for purposes of this Registration Statement to the extent
that a statement contained in this Registration Statement or in any subsequently
filed document that is deemed to be incorporated by reference in this
Registration Statement modifies or supersedes such statement.

ITEM 4. DESCRIPTION OF SECURITIES.

     Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

     Not applicable.

ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     The Registrant's Amended and Restated Articles of Incorporation limit the
liability of the Registrant's directors for monetary damages to the maximum
extent permitted by California law. Such limitation of liability has no effect
on the availability of equitable remedies, such as injunctive relief or
rescission.

     The Registrant's Amended and Restated Bylaws provide that the Registrant
will indemnify its directors and officers and may indemnify its employees and
agents (other than officers and directors) against

<PAGE>   3

certain liabilities to the maximum extent permitted by California law. The
Registrant has entered into indemnification agreements with each of its current
directors and officers and certain of its key employees that provide for
indemnification of, and advancement of expenses to, such persons to the maximum
extent permitted by California law, including by reason of action or inaction
occurring in the past and circumstances in which indemnification and advancement
of expenses are discretionary under California law.

     At the present time, there is no pending litigation or proceeding involving
a director, officer, employee or other agent of the Registrant in which
indemnification would be required or permitted. The Registrant is not aware of
any threatened litigation or proceeding that may result in a claim for such
indemnification.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

     Not applicable.

ITEM 8. EXHIBITS.

<TABLE>
<CAPTION>
Exhibit
Number     Description
-------    -----------
<S>        <C>
  5.1      Opinion of Wilson Sonsini Goodrich & Rosati
 10.1      1992 ISOCOR Stock Option Plan
 10.2      1996 ISOCOR Directors' Stock Option Plan
 10.3      1999 ISOCOR Stock Option Plan
 23.1      Consent of PricewaterhouseCoopers LLP, Independent Accountants
 23.2      Consent of Ernst & Young LLP, Independent Auditors
 23.3      Consent of Wilson Sonsini Goodrich & Rosati (contained in
             Exhibit 5.1)
 24.1      Power of Attorney (see signature page)
</TABLE>

ITEM 9. UNDERTAKINGS.

     1. The Registrant hereby undertakes:

          (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this Registration Statement to include any
material information with respect to the plan of distribution not previously
disclosed in the Registration Statement or any material change to such
information in the Registration Statement.

          (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

          (3) To remove from registration by means of a post-effective amendment
any of the securities being registered which remain unsold at the termination of
the offering.

     2. The Registrant hereby undertakes that, for purposes of determining any
liability under the Securities Act, each filing of the Registrant's annual
report pursuant to Section 13(a) or Section 15(d) of the Exchange Act that is
incorporated by reference in the Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.


                                      -2-
<PAGE>   4

     3. Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
Registrant pursuant to law, the Registrant's Articles of Incorporation, Bylaws
or indemnification agreements, the Registrant has been advised that in the
opinion of the Commission such indemnification is against public policy as
expressed in the Securities Act and is therefore unenforceable. In the event
that a claim for indemnification against such liabilities (other than the
payment by the Registrant of expenses incurred or paid by a director, officer or
controlling person of the Registrant in a successful defense of any action, suit
or proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered hereunder, the Registrant will,
unless in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question of whether
such indemnification by it is against public policy as expressed in the
Securities Act and will be governed by the final adjudication of such issue.


                                      -3-
<PAGE>   5

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of San Francisco, State of California, on January 19,
2000.

                                      CRITICAL PATH, INC.

                                   By: /s/ Douglas T. Hickey
                                      ------------------------------------------
                                      Douglas T. Hickey
                                      President and Chief Executive Officer


                                POWER OF ATTORNEY

     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Douglas T. Hickey and David Thatcher, or either
of them, his or her attorney-in-fact, with the power of substitution, for him or
her in any and all capacities, to sign any amendments to this Registration
Statement on Form S-8, and to file the same, with exhibits thereto and other
documents in connection therewith, with the Securities and Exchange Commission,
hereby ratifying and confirming all that each of said attorneys-in- fact, or his
substitute or substitutes, may do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
      SIGNATURE                              TITLE                                   DATE
      ---------                              -----                                   ----
<S>                          <C>                                                <C>
/s/ Douglas T. Hickey        President and Chief Executive Officer and          January 19, 2000
------------------------     Director (Principal Executive Officer)
  Douglas T. Hickey

 /s/ David Thatcher          Executive Vice President and Chief Financial       January 19, 2000
------------------------     Officer (Principal Financial and Accounting
    David Thatcher           Officer)

 /s/ David C. Hayden         Chairman of the Board                              January 19, 2000
------------------------
   David C. Hayden

/s/ Christos M. Cotsakos     Director                                           January 19, 2000
------------------------
 Christos M. Cotsakos

                             Director                                           January   , 2000
------------------------
     Lisa Gansky

/s/ Kevin R. Harvey          Director                                           January 19, 2000
------------------------
   Kevin R. Harvey

/s/ James A. Smith           Director                                           January 19, 2000
------------------------
    James A. Smith

/s/ George Zachary           Director                                           January 19, 2000
------------------------
    George Zachary
</TABLE>


                                      -4-
<PAGE>   6

                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>
EXHIBIT
NUMBER     DESCRIPTION
------     -----------
<S>        <C>
  5.1      Opinion of Wilson Sonsini Goodrich & Rosati
 10.1      1992 ISOCOR Stock Option Plan
 10.2      1996 ISOCOR Directors' Stock Option Plan
 10.3      1999 ISOCOR Stock Option Plan
 23.1      Consent of PricewaterhouseCoopers LLP, Independent Accountants
 23.2      Consent of Ernst & Young LLP, Independent Auditors
 23.3      Consent of Wilson Sonsini Goodrich & Rosati (contained in
             Exhibit 5.1)
 24.1      Power of Attorney (see signature page)
</TABLE>


                                      -5-
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 16272}]
{"company-data": {"conformed-name": "CRITICAL PATH INC", "cik": "0001060801", "assigned-sic": "7389", "irs-number": "911788300", "state-of-incorporation": "CA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-95279", "film-number": "512052"}, "business-address": {"street1": "320 FIRST STREET", "city": "SAN FRANCISCO", "state": "CA", "zip": "94105", "phone": "4158088800"}, "mail-address": {"street1": "320 FIRST STREET", "city": "SAN FRNACISCO", "state": "CA", "zip": "94105"}}
1

        As filed with the Securities and Exchange Commission on January 24, 2000
                                                     Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                -----------------
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                -----------------

                               CRITICAL PATH, INC
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                -----------------

                                                 320 FIRST STREET
           CALIFORNIA                    SAN FRANCISCO, CALIFORNIA 94105
    ------------------------        ----------------------------------------
    (STATE OF INCORPORATION)        (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)

                          1992 ISOCOR STOCK OPTION PLAN
                    1996 ISOCOR DIRECTORS' STOCK OPTION PLAN
                          1999 ISOCOR STOCK OPTION PLAN
                            (FULL TITLE OF THE PLANS)

                                -----------------

                                DOUGLAS T. HICKEY
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                               CRITICAL PATH, INC.
                                 320 1ST STREET
                         SAN FRANCISCO, CALIFORNIA 94105
                                 (415) 808-8800
(NAME, ADDRESS, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)
                                -----------------
                                   Copies to:
                              Alan K. Austin, Esq.
                             Mark L. Reinstra, Esq.
                        Wilson Sonsini Goodrich & Rosati
                            Professional Corporation
                               650 Page Mill Road
                               Palo Alto, CA 94304
                                 (650) 493-9300
                                -----------------
                         CALCULATION OF REGISTRATION FEE
==========================================================================================================================
                                                       MAXIMUM      PROPOSED MAXIMUM   PROPOSED MAXIMUM
                                                    AMOUNT TO BE        OFFERING           AGGREGATE          AMOUNT OF
TITLE OF SECURITIES TO BE REGISTERED                REGISTERED(1)    PRICE PER SHARE    OFFERING PRICE    REGISTRATION FEE
------------------------------------------------   --------------   ----------------   ----------------   ----------------
Common Stock, par value $0.001                     764,583 shares       $ 6.87(2)       $ 5,252,685.21        $1,386.71

     to be issued upon exercise of options
        granted under the 1992 ISOCOR Stock
        Option Plan...........................

     to be issued upon exercise of options
        granted under the 1996 ISOCOR Directors'    30,591 shares       $11.61(3)       $   355,161.51        $   93.76
        Stock Option Plan.....................

     to be issued upon exercise of options
        granted and outstanding and options        197,910 shares       $53.89(4)       $10,665,369.90        $2,815.66
        authorized and unissued under the 1999
        ISOCOR Stock Option Plan..............

             TOTAL............................     993,084 shares                       $15,996,697.20        $4,296.13
==========================================================================================================================
(1) This Registration Statement shall also cover any additional shares of Common
    Stock which become issuable under the Plan being registered pursuant to this
    Registration Statement by reason of any stock dividend, stock split,
    recapitalization or any other similar transaction effected without the
    receipt of consideration which results in an increase in the number of the
    Registrant's outstanding shares of Common Stock.

(2) Computed in accordance with Rules 457(h) and 457(c) under the Securities Act
    of 1933. Such computation is based on the weighted average exercise price of
    $6.87 per share covering 764,583 outstanding options.

(3) Computed in accordance with Rules 457(h) and 457(c) under the Securities Act
    of 1933. Such computation is based on the weighted average exercise price of
    $11.61 per share covering 30,591 outstanding options.

(4) Computed in accordance with Rules 457(h) and 457(c) under the Securities Act
    of 1933. Such computation is based on the weighted average exercise price of
    $17.14 per share covering 56,700 outstanding options and the estimated
    exercise price of $68.63 per share covering 141,210 authorized but unissued
    shares. The estimated exercise price of $68.63 per share was computed in
    accordance with Rule 457 by averaging the high and low prices of a share of
    Critical Path, Inc. Common Stock as reported on the Nasdaq National Market
    on January 14, 2000.
2

                               CRITICAL PATH, INC.

                       REGISTRATION STATEMENT ON FORM S-8

                                     PART II

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

     The following documents previously filed by Critical Path, Inc. (the
"Registrant") with the Securities and Exchange Commission (the "SEC") are hereby
incorporated by reference in this Registration Statement:

          (a) The Registrant's Quarterly Report on Form 10-Q for the fiscal
quarter ended September 30, 1999;

          (b) The Registrant's Quarterly Report on Form 10-Q for the fiscal
quarter ended June 30, 1999;

          (c) Prospectus of the Registrant, dated June 1, 1999;

          (d) The Registrant's Quarterly Report on Form 10-Q for the fiscal
quarter ended March 31, 1999;

          (e) The description of the Registrant's Common Stock contained in the
Registrant's Registration Statement on Form 8-A, dated February 1, 1999.

     All documents filed by the Registrant pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Securities Exchange Act of 1934, as amended, on or after the
date of this Registration Statement prior to the filing of a post-effective
amendment which indicates that all securities offered hereby have been sold or
which deregisters all securities then remaining unsold, shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of the filing of such documents.

     Any statement contained in this Registration Statement or in a document
incorporated by reference in this Registration Statement shall be deemed to be
modified or superseded for purposes of this Registration Statement to the extent
that a statement contained in this Registration Statement or in any subsequently
filed document that is deemed to be incorporated by reference in this
Registration Statement modifies or supersedes such statement.

ITEM 4. DESCRIPTION OF SECURITIES.

     Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

     Not applicable.

ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     The Registrant's Amended and Restated Articles of Incorporation limit the
liability of the Registrant's directors for monetary damages to the maximum
extent permitted by California law. Such limitation of liability has no effect
on the availability of equitable remedies, such as injunctive relief or
rescission.

     The Registrant's Amended and Restated Bylaws provide that the Registrant
will indemnify its directors and officers and may indemnify its employees and
agents (other than officers and directors) against
3

certain liabilities to the maximum extent permitted by California law. The
Registrant has entered into indemnification agreements with each of its current
directors and officers and certain of its key employees that provide for
indemnification of, and advancement of expenses to, such persons to the maximum
extent permitted by California law, including by reason of action or inaction
occurring in the past and circumstances in which indemnification and advancement
of expenses are discretionary under California law.

     At the present time, there is no pending litigation or proceeding involving
a director, officer, employee or other agent of the Registrant in which
indemnification would be required or permitted. The Registrant is not aware of
any threatened litigation or proceeding that may result in a claim for such
indemnification.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

     Not applicable.

ITEM 8. EXHIBITS.
Exhibit
Number     Description
-------    -----------
5.1      Opinion of Wilson Sonsini Goodrich & Rosati
 10.1      1992 ISOCOR Stock Option Plan
 10.2      1996 ISOCOR Directors' Stock Option Plan
 10.3      1999 ISOCOR Stock Option Plan
 23.1      Consent of PricewaterhouseCoopers LLP, Independent Accountants
 23.2      Consent of Ernst & Young LLP, Independent Auditors
 23.3      Consent of Wilson Sonsini Goodrich & Rosati (contained in
             Exhibit 5.1)
 24.1      Power of Attorney (see signature page)
ITEM 9. UNDERTAKINGS.

     1. The Registrant hereby undertakes:

          (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this Registration Statement to include any
material information with respect to the plan of distribution not previously
disclosed in the Registration Statement or any material change to such
information in the Registration Statement.

          (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

          (3) To remove from registration by means of a post-effective amendment
any of the securities being registered which remain unsold at the termination of
the offering.

     2. The Registrant hereby undertakes that, for purposes of determining any
liability under the Securities Act, each filing of the Registrant's annual
report pursuant to Section 13(a) or Section 15(d) of the Exchange Act that is
incorporated by reference in the Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

                                      -2-
4

     3. Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
Registrant pursuant to law, the Registrant's Articles of Incorporation, Bylaws
or indemnification agreements, the Registrant has been advised that in the
opinion of the Commission such indemnification is against public policy as
expressed in the Securities Act and is therefore unenforceable. In the event
that a claim for indemnification against such liabilities (other than the
payment by the Registrant of expenses incurred or paid by a director, officer or
controlling person of the Registrant in a successful defense of any action, suit
or proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered hereunder, the Registrant will,
unless in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question of whether
such indemnification by it is against public policy as expressed in the
Securities Act and will be governed by the final adjudication of such issue.

                                      -3-
5

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of San Francisco, State of California, on January 19,
2000.

                                      CRITICAL PATH, INC.

                                   By: /s/ Douglas T. Hickey
                                      ------------------------------------------
                                      Douglas T. Hickey
                                      President and Chief Executive Officer

                                POWER OF ATTORNEY

     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Douglas T. Hickey and David Thatcher, or either
of them, his or her attorney-in-fact, with the power of substitution, for him or
her in any and all capacities, to sign any amendments to this Registration
Statement on Form S-8, and to file the same, with exhibits thereto and other
documents in connection therewith, with the Securities and Exchange Commission,
hereby ratifying and confirming all that each of said attorneys-in- fact, or his
substitute or substitutes, may do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the dates indicated.
SIGNATURE                              TITLE                                   DATE
      ---------                              -----                                   ----
/s/ Douglas T. Hickey        President and Chief Executive Officer and          January 19, 2000
------------------------     Director (Principal Executive Officer)
  Douglas T. Hickey

 /s/ David Thatcher          Executive Vice President and Chief Financial       January 19, 2000
------------------------     Officer (Principal Financial and Accounting
    David Thatcher           Officer)

 /s/ David C. Hayden         Chairman of the Board                              January 19, 2000
------------------------
   David C. Hayden

/s/ Christos M. Cotsakos     Director                                           January 19, 2000
------------------------
 Christos M. Cotsakos

                             Director                                           January   , 2000
------------------------
     Lisa Gansky

/s/ Kevin R. Harvey          Director                                           January 19, 2000
------------------------
   Kevin R. Harvey

/s/ James A. Smith           Director                                           January 19, 2000
------------------------
    James A. Smith

/s/ George Zachary           Director                                           January 19, 2000
------------------------
    George Zachary
-4-
6

                                INDEX TO EXHIBITS
EXHIBIT
NUMBER     DESCRIPTION
------     -----------
5.1      Opinion of Wilson Sonsini Goodrich & Rosati
 10.1      1992 ISOCOR Stock Option Plan
 10.2      1996 ISOCOR Directors' Stock Option Plan
 10.3      1999 ISOCOR Stock Option Plan
 23.1      Consent of PricewaterhouseCoopers LLP, Independent Accountants
 23.2      Consent of Ernst & Young LLP, Independent Auditors
 23.3      Consent of Wilson Sonsini Goodrich & Rosati (contained in
             Exhibit 5.1)
 24.1      Power of Attorney (see signature page)
-5-