<PAGE>

                                                                   EXHIBIT 4.3


NEITHER THE SECURITY EVIDENCED BY THIS WARRANT NOR THE SECURITIES ISSUABLE UPON
EXERCISE OF THIS WARRANT HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
AS AMENDED, OR ANY APPLICABLE STATE LAW, AND NO INTEREST HEREIN OR THEREIN MAY
BE SOLD, DISTRIBUTED, ASSIGNED, OFFERED, PLEDGED OR OTHERWISE TRANSFERRED UNLESS
(A) THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT AND APPLICABLE
STATE SECURITIES LAWS COVERING ANY SUCH TRANSACTION INVOLVING SAID SECURITIES,
(B) THE COMPANY RECEIVES OPINION OF LEGAL COUNSEL FOR THE HOLDER OF SAID
SECURITIES (REASONABLY ACCEPTABLE TO THE COMPANY) STATING THAT SUCH TRANSACTION
IS EXEMPT FROM REGISTRATION, OR (C) THE COMPANY OTHERWISE SATISFIES ITSELF THAT
SUCH TRANSACTION IS EXEMPT FROM REGISTRATION.

No. ____

ISSUED: October 20, 1999



                               CRITICAL PATH, INC.


                          COMMON STOCK PURCHASE WARRANT


        THIS IS TO CERTIFY that, subject to the terms and conditions hereof,
U.S. Telesource, Inc., a Delaware corporation (the "Holder"), or its assigns is
entitled to subscribe for and purchase from Critical Path, Inc., a California
corporation (the "Company"), at any time on or after the date hereof but not
later than 5:00 p.m., San Francisco time, on October 19, 2007 (the "Exercise
Period"), subject to the provisions hereof, up to a maximum of 3,543,539 shares
(subject to adjustment as provided herein) (the "Warrant Shares" ) of fully paid
and non-assessable shares of Common Stock, $.001 par value, of the Company (the
"Common Stock"), at a price per share (the "Exercise Price") as set forth in
Section 1.1 hereto. This Warrant is being issued pursuant to a certain Master
Agreement dated as of October 20, 1999, between Qwest Communications
Corporation, a Delaware corporation, and the Company (the "Master Agreement").
All capitalized terms used but not otherwise defined herein shall have the
meaning ascribed to such terms in the Master Agreement.


                               SECTION 1 EXERCISE


        1.1 Warrant Shares Eligible to be Purchased

                (a) Subject to the provisions of Sections 1.2, 1.3, 1.4 and 12,
                the Holder's rights to purchase Warrant Shares during the
                Exercise Period shall vest and the Exercise Price for such
                Warrant Shares shall be determined as set forth in the table
                below. For the purposes of determining the vesting requirements,
                a "Qwest Service Email Box" shall mean an email box registered
                by Qwest utilizing Critical Path's Services, as provided in
                Article 3 of the Master Agreement, provided that all such Qwest
                Email Service Boxes shall be Critical Path sub-branded. For the
                purposes of determining the Exercise Price, the "Closing Price"
                shall mean the closing price of Company Common Stock, as


                                      -1-
<PAGE>

                average of the closing bid and asked prices of the Common Stock
                as quoted in the Over-the-Counter Market Summary or the last
                reported sale price of the Common Stock or the closing price
                quoted on the Nasdaq national market system, on the last trading
                day National Market System or on any exchange on which the
                Common Stock is then listed, whichever is applicable, for the
                fifteen (15) trading days prior to the day in question.



<TABLE>
<CAPTION>
Number of Shares                         Vesting                                Exercise Price
----------------                         -------                                --------------
<S>                                     <C>                                    <C>
589,090 shares, or one-sixth of          The registration of the                The Closing Price for the
the Warrant Shares.                      400,000th Qwest Service                Effective Date (the "Initial
                                         Email Box Upon execution of            Exercise Price") ($41.581)
                                         this Warrant.

589,090 shares, or one-sixth of          The registration of the                The Initial Exercise Price plus
the Warrant Shares.                      400,000th Qwest Service                $3.00 ($44.581)
                                         Email Box.

589,090 shares, or one-sixth of          The registration of the                The Initial Exercise Price plus
the Warrant Shares.                      800,000th Qwest Service                $6.00 ($47.581)
                                         Email Box.

589,090 shares, or one-sixth of          The registration of the                The Initial Exercise Price plus
the Warrant Shares.                      1,200,000th Qwest Service              $9.00 ($50.581)
                                         Email Box.

589,090 shares, or one-sixth of          The registration of the                The Initial Exercise Price plus
the Warrant Shares.                      1,600,000th Qwest Service              $12.00 ($53.581)
                                         Email Box.

589,090 shares, or one-sixth of          The registration of the                The Initial Exercise Price plus
the Warrant Shares.                      2,000,000th Qwest Service              $15.00 ($56.581)
                                         Email Box.
</TABLE>


                (b) Notwithstanding anything herein to the contrary, if any
                portion of the Warrant Shares shall not have vested (in
                accordance with the table set forth in Section 1(a) above)
                within three years from the date of the Master Agreement, then
                the Holder's right to purchase such portion of the Warrant
                Shares shall terminate.

                (c) Notwithstanding the foregoing, any portion of the Warrant
                Shares that have vested (in accordance with the table set forth
                in Section 1(a) above) shall be exercisable for a period of five
                years commencing on the date such portion of the Warrant Shares
                vested, and thereafter any such rights to exercise such portion
                of the Warrant Shares shall terminate.

        1.2 Procedure for Exercise

        Subject to the foregoing, this Warrant may be exercised by the Holder,
as to those shares of Warrant Shares for which this Warrant is then exercisable
as determined in accordance with Section 1.1, at any time during the Exercise
Period in whole or part by delivering to the Company, at the address of the
Company set forth in Section 17, (a) the form of Exercise Notice attached hereto
duly completed and executed by the Holder, (b) this Warrant certificate, (c)
cash or a bank cashier's check payable to the Company in the amount of the
Exercise Price multiplied by the number of shares for which this Warrant is
being exercised (the "Purchase Price"), and



                                      -2-
<PAGE>


(d), a certificate signed by an appropriate officer of the Holder setting forth
the amount of all outstanding securities, including rights, options, or warrants
to acquire securities of the Company, that are owned by the Holder, and any
Subsidiary (as defined in Section 16) of the Holder, in order to assure
compliance with Section 1.4 below. The Holder will be deemed to be the holder of
record of the shares of Common Stock as to which the Warrant was exercised in
accordance with this Warrant, effective at the close of business, San Francisco
time, on the date such exercise is completed and all documents specified above
are delivered to the Company.

        1.3 Net Exercise

        Notwithstanding the payment provisions set forth above, the Holder may
elect to exercise this Warrant by converting this Warrant into shares of Warrant
Shares as provided in this Section 1.3, such election to be effected by
surrender of this Warrant at the principal office of the Company, together with
the Notice of Exercise indicating such election, in which case the Company shall
issue to the Holder the number of shares of Warrant Shares determined as
follows:

                               X  = Y (A-B)
                                    -------
                                       A

Where:          X = the number of shares of Warrant Shares to be issued

                Y = the number of shares of Warrant Shares as to which the
                Warrant is being exercised

                A = the Fair Market Value (as defined below) of one (1) share of
                Warrant Shares

                B = the applicable Exercise Price

                For purposes of the above calculation, the Fair Market Value of
        a share of Warrant Shares shall be determined in good faith by the Board
        of Directors of the Company (the "Board"); provided, however, that if a
        public market for the common stock of Company (the "Common Stock")
        exists at the time of such exercise, then such Fair Market Value shall
        be the average of the closing bid and asked prices of the Common Stock
        as quoted in the Over-the-Counter Market Summary or the last reported
        sale price of the Common Stock or the closing price quoted on the Nasdaq
        National Market System or on any exchange on which the Common Stock is
        then listed, whichever is applicable, for the five (5) trading days
        prior to the date of exercise of this Warrant. The Board shall promptly
        respond in writing to an inquiry by the Holder as to the Fair Market
        Value of one share of Warrant Shares.

        1.4 Restrictions on Exercise

        This Warrant shall not be exercisable as to any portion of the Warrant
Shares that would cause, on the date of the vesting of each one-sixth of the
Warrant Shares (as described in Section 1.1) (each a "Vesting Date"), the Holder
and any Affiliate (as defined in the Master Agreement) thereof to own, in the
aggregate, 10% or more of the Fully-Diluted Stock (as defined in Section 1.5
below) of the Company. Subject to the next two succeeding sentences, if on the
Exercise Date such restriction is applicable, the Warrant shall be exercisable
for a number of Warrant Shares equal to the remainder of (x) the number of
shares equal to 9.9% of the Fully-Diluted Stock of the Company minus (y) the
number of shares of Common Stock then owned in the aggregate by the Holder and
any Affiliate (the "Maximum Number of Warrant Shares"). The Holder's right to
purchase any vested Warrant Shares in excess of the Maximum Number of



                                      -3-
<PAGE>


Warrant Shares will terminate on the date that is six months after the most
recent Vesting Date, except that with respect to the last Vesting Date, such
right will terminate thereon.

        1.5 Representation of Company Regarding the Equity Percentage of the
Warrants

        The Company represents to Holder that, as of the date of the Master
Agreement (the "Designated Date"), the Warrant Shares, if all issued as of the
Designated Date, would constitute six percent (6%) of the number of shares of
voting capital stock of the Company on the Designated Date after giving effect
to the exercise, exchange or conversion of all outstanding securities, rights,
options, warrants (including this Warrant), calls, commitments or agreements of
any nature or character (whether debt or equity) that are, directly or
indirectly, exercisable or exchangeable for, or convertible into or otherwise
represent the right to purchase or otherwise receive, directly or indirectly,
any such capital stock or other arrangement to acquire at any time or under any
circumstance, voting capital stock of the Company or any such other outstanding
securities and including all shares or other equity interests subject, as of the
Designated Date to issued stock options or other rights to acquire equity of any
nature to officers, directors, employees or consultants of the Company under all
agreements, plans or arrangements theretofore approved by the Board of Directors
of the Company, whether on not the right to exercise such outstanding options or
other rights is currently effective or vested (collectively, the "Fully-Diluted
Stock").

                     SECTION 2 DELIVERY OF STOCK CERTIFICATE

        Within 20 days after the exercise of this Warrant (in full or in part)
and payment of the Purchase Price then due, the Company at its expense shall
issue in the name of and deliver to the Holder (a) a certificate or certificates
for the number of fully paid and nonassessable shares of Warrant Shares to which
the Holder shall be entitled upon such exercise and (b) if applicable, a new
Warrant of like tenor to purchase up to that number of shares of Warrant Shares,
if any, as to which this Warrant shall not have been previously exercised by the
Holder or repurchased by the Company.

                    SECTION 3 COVENANTS AS TO WARRANT SHARES

        The Company covenants and agrees that the Company will at all times have
authorized and reserved a sufficient number of shares of Common Stock to provide
for the exercise of the rights represented by this Warrant. The Company further
covenants that all shares of Common Stock which may be issued upon the exercise
of the rights represented by this Warrant, will, upon issuance, in accordance
with the terms of this Warrant, be validly issued, fully paid and non-assessable
and free from all taxes, liens and charges solely with respect to the issuance
thereof. The Company further covenants and agrees that the Company will from
time to time take all such action as may be requisite to assure that the stated
or par value per share of the Common Stock is at all times equal to or less than
the then effective Exercise Price per share of the Common Stock issuable upon
exercise of this Warrant. If and so long as the Common Stock issuable upon
exercise of the rights represented by this Warrant is listed on any national
securities exchange, the Company will, if permitted by the rules of such
exchange, use its best efforts to list and keep listed on such exchange, upon
official notice of issuance, all Warrant Shares.


                                      -4-
<PAGE>

                       SECTION 4 EFFECTS OF REORGANIZATION

        In the event of a merger or consolidation of the Company with another
entity or the acquisition of all or substantially all of the assets or stock of
the Company by another entity (collectively such events being a
"Reorganization"), the following provisions will apply:

        (a) The Holder will be provided with notice of such Reorganization at
        the same time as notice is provided to the Company's shareholders. In
        addition, the Holder will be provided copies of any notice sent to
        shareholders of the Company in connection with such Reorganization
        (including notice of any shareholder's meetings and shareholder's
        consents), simultaneously with such notice being provided to any
        shareholder.

        (b) In the event the shareholders of the Company receive cash, stock or
        other property or contractual rights in respect of their stock in the
        Company (including upon any Reorganization where the Company is not the
        surviving entity), this Warrant will be exchanged for a warrant to
        purchase such kind and number of shares of capital stock or other
        securities or property or rights of the Company or the surviving entity
        to which the Holder would have been entitled if it had held the Common
        Stock issuable upon the exercise hereof immediately prior to such
        Reorganization, which warrant shall have the same terms and conditions
        hereof; provided, however, that if the Holder does not receive such
        warrant in exchange for this Warrant, then the Warrant will vest and
        become fully exercisable with respect to the maximum number of Warrant
        Shares upon completion of the Reorganization and the Holder will be
        entitled to exercise such Warrant Shares effective concurrently with
        completion of the Reorganization (but immediately prior thereto).
        Despite the foregoing, if the sole consideration received by
        shareholders in any such Reorganization is cash, then Company shall not
        be required to issue an exchange warrant if it pays to the Holder,
        immediately upon closing, cash based on the amount that the Holder would
        have received in such Reorganization upon full exercise of the Warrant
        for all Warrant Shares then vested; it being understood that the net
        amount payable will be the net exercise price therefor calculated in the
        manner specified in Section 1.3 above.

           SECTION 5 ADJUSTMENTS FOR STOCK SPLITS AND SIMILAR MATTERS

        5.1 Stock Splits and Reverse Stock Splits

        If the Company shall issue any shares of Common Stock as a stock
dividend or subdivide the number of outstanding shares of Common Stock into a
greater number of shares, then, in either such case, then the Exercise Price in
effect before such dividend or subdivision shall be proportionately reduced and
the number of shares of Warrant Shares at that time purchasable pursuant to this
Warrant shall be proportionately increased; and, conversely, if the Company
shall reduce the number of outstanding shares of Common Stock by combining such
shares into a smaller number of shares, then the Exercise Price in effect before
such combination shall be proportionately increased and the number of shares of
Warrant Shares at that time purchasable pursuant to this Warrant shall be
proportionately decreased. Upon each adjustment in the Exercise Price pursuant
to this Section 5, the number of shares of Warrant Shares purchasable hereunder
shall be adjusted, to the nearest whole share, to the product obtained by
multiplying such number of shares purchasable immediately prior to such
adjustment in the Exercise Price by a fraction, the numerator of which shall be
the Exercise Price immediately prior to such



                                      -5-
<PAGE>

adjustment and the denominator of which shall be the Exercise Price immediately
thereafter. The Holder shall be entitled to the same notice and information
regarding such dividend or subdivision as is furnished to holders of Common
Stock, which notice shall be sent to the Holder no later than the date such
notice is sent to all holders of Common Stock. The foregoing is intended to
protect Holder against dilution due to stock dividends and stock splits.

        5.2 Other Dividends and Distributions

        In case the Company shall take a record of the holders of its Common
Stock (or other stock or securities at the time receivable upon the exercise of
this Warrant) for the purpose of entitling them to receive any dividend or other
distribution other than as described in Section 5.1, or any right to subscribe
for or purchase any shares of stock of any class or any other securities, or to
receive any other right, then the Company will mail or cause to be mailed to the
Holder a notice specifying the date on which a record is to be taken for the
purpose of such dividend, distribution or right (the "Record Date"), and stating
the amount and character of such dividend, distribution or right. Such notice
shall be mailed at least 15 days prior to the Record Date therein specified.

                           SECTION 6 CHANGE OF CONTROL

        Upon a Change of Control (as defined below) of the Company, the
restrictions on exercise as described in Section 1.4 will terminate.

        For the purposes of this Warrant, "Change of Control" of the Company
        means: (i) an acquisition of Common Stock and any other securities
        issued by the Company having the ordinary power to vote in the election
        of directors of the Company (other than securities having such power
        only upon the happening of a contingency) (the "Voting Stock") by any
        person, individual, corporation, partnership, trust or other
        non-governmental entity or any governmental agency, court, authority or
        other body (whether foreign, federal, state, local or otherwise)
        (collectively, "Person") or a Group (as that term has the meaning
        comprehended by Section 13(d)(3) of the Securities Exchange Act of 1934,
        as amended, and the rules and regulations promulgated thereunder (the
        "Exchange Act")) (other than the Company or its affiliates) in a
        purchase or transaction or series of related purchases or transactions
        if immediately thereafter such Person or Group has Beneficial Ownership
        (as such term has the meaning comprehended by Section 13(d)(3) of the
        Exchange Act) of more than fifty percent (50%) of the combined voting
        power of the Company's then outstanding Voting Stock; (ii) the execution
        of an agreement providing for a tender offer, merger, consolidation or
        reorganization, or series of such related transactions involving the
        Company, unless the stockholders of the Company, immediately after such
        transaction or transactions are Beneficial Owners of at least fifty
        percent (50%) of the Voting Stock; (iii) a change or changes in the
        membership of the Company's board of directors that represents a change
        of a majority or more of such membership during any twelve month period
        (unless such change or changes in membership are caused by actions of
        the then existing board of directors and do not occur within twelve
        months of the commencement, threat or proposal of an Election Contest
        (as such term is defined in Rule 14a-11 of Regulation 14A under the
        Exchange Act), tender offer or other transaction that would constitute a
        Change of Control under (i) or (ii) of this paragraph; or (iv) to the
        extent not covered by (i), (ii) or (iii) of this paragraph, any event
        constituting a Reorganization under Section 4.



                                      -6-
<PAGE>

                          SECTION 7 FRACTIONAL SHARES

        No fractional shares shall be issued upon the exercise of this Warrant.
In lieu of fractional shares, the Company shall pay the Holder a sum in cash
equal to the fair market value of the fractional shares on the date of exercise.

                       SECTION 8 RESTRICTIONS ON TRANSFER

        Neither the Security evidenced by this Warrant nor the securities
issuable upon exercise of this Warrant may be transferred unless (a) there is an
effective registration statement under the Securities Act of 1933, as amended
(the "Securities Act"), and applicable state securities laws covering any such
transaction involving said securities, (b) the Company receives opinion of legal
counsel for the holder of said securities (reasonably acceptable to the Company)
stating that such transaction is exempt from registration; provided, however,
that no such opinion of counsel shall be necessary for a transfer of Warrant
Shares pursuant to Rule 144(k) promulgated under the Securities Act or any
successor rule thereto ("Rule 144(k)"), or (c) the Company otherwise satisfies
itself that such transaction is exempt from registration. The Holder and Company
agree that all Warrant Shares shall have the same registration rights and be
subject to the same terms and conditions with respect to the registration and
sale of such stock as provided for in the Amended and Restated Investors' Rights
Agreement dated September 11, 1998 among the Company and the individuals and
entities listed on the signature pages thereto, as amended by the Amendment to
Amended and Restated Investors' Rights Agreement dated January 13, 1999 among
the Company and the individuals and entities listed on the signature pages
thereto (together, the "Rights Agreement"), and as possessed by the individuals
and entities listed on the signature pages to the Rights Agreement.

                                SECTION 9 LEGEND

        A legend setting forth or referring to the foregoing restrictions shall
be placed on this Warrant, any replacement hereof and any certificate
representing a security issued pursuant to the exercise hereof, and a stop
transfer restriction or order shall be placed on the books of the Company and
with any transfer agent until such securities may be legally sold or otherwise
transferred; provided, however, that such legend shall not be required and a
stop transfer restriction order shall not be placed if (a) in the opinion of
counsel to the Holder (reasonably acceptable to the Company) registration of any
future transfer is not required by the applicable provisions of the Securities
Act, (b) the Company shall have waived the requirements of such legends, or (c)
the transfer of Warrant Shares shall be made in compliance with the requirements
of Rule 144(k) or the Company otherwise satisfies itself that such transaction
is exempt from registration.

                           SECTION 10 HOLDER AS OWNER

        The Company may deem and treat the Holder of this Warrant as the
absolute owner hereof for all purposes regardless of any notice to the contrary.



                                      -7-
<PAGE>

                        SECTION 11 WARRANT HOLDER RIGHTS

        This Warrant shall not entitle the Holder to any voting rights or any
other rights as a shareholder of the Company or to any other rights whatsoever
except the rights stated herein; and except as otherwise provided herein, no
dividend or interest shall be payable or shall accrue in respect of this Warrant
or the Warrant Shares purchasable hereunder unless, until and to the extent that
this Warrant shall be exercised.

                             SECTION 12 CONSTRUCTION

        The validity and interpretation of the terms and provisions of this
Warrant shall be governed by the laws of the State of California without respect
to the conflicts of laws principles thereof. The descriptive headings of the
several sections of this Warrant are inserted for convenience only and shall not
control or affect the meaning or construction of any of the provisions thereof.

                              SECTION 13 EXPIRATION

        Subject to the last sentence of Section1.4, any portion of the Warrant
Shares which shall not have become exercisable (in Accordance with the table set
forth in Section 1.1 (a) above) within three years from the date of the Master
Agreement shall be cancelled. Notwithstanding the above, any portion of the
Warrant Shares that have become exercisable (in accordance with the table set
forth in Section 1(a) above) shall be exercisable for a period of five years
commencing on the date such portion of the Warrant Shares became exercisable.
All restrictions set forth herein on the shares of capital stock issued upon
exercise of any rights hereunder shall survive such exercise and expiration of
the rights granted hereunder.

                         SECTION 14 EXCHANGE OF WARRANT

        This Warrant is exchangeable upon the surrender hereof by the Holder at
the office of the Company for new Warrants of like tenor representing in the
aggregate the rights to subscribe for and purchase the number of shares which
may be subscribed for and purchased hereunder, each of such new Warrants to
represent the right to subscribe for and purchase such number of shares as shall
be designated by the Holder at the time of such surrender.

                       SECTION 15 LOST WARRANT CERTIFICATE

        If this Warrant is lost, stolen, mutilated or destroyed, the Company
shall, upon request in writing from the Holder and subject to compliance by
Holder with the following sentence, issue a new Warrant of like denomination,
tenor and date as this Warrant, subject to the Company's right to require the
Holder to give the Company a bond or other satisfactory security sufficient to
indemnify the Company against any claim that may be made against it (including
any expense or liability) on account of the alleged loss, theft, mutilation or
destruction of this Warrant or the issuance of such new Warrant. The Holder
shall reimburse the Company for any and all expenses and costs incurred by the
Company in connection with issuing a new Warrant under this Section.



                                      -8-
<PAGE>

                        SECTION 16 WAIVERS AND AMENDMENTS

        This Warrant or any provision hereof may be changed, waived, discharged
or terminated only by a statement in writing signed by the party against which
enforcement of the change, waiver, discharge or termination is sought.

                        SECTION 17 SUCCESSORS AND ASSIGNS

        This Warrant shall be binding upon the Company and inure to the benefit
of the Holder and its successors and assigns; provided, however, that the
Warrant shall only be assignable by the Holder to its Affiliates (as defined in
the Master Agreement).

                               SECTION 18 NOTICES

        All notices or other communications required or permitted hereunder
shall be in writing and shall be delivered by personal delivery, reputable
overnight courier service, telecopier or mailed by United States mail,
first-class postage prepaid, or by registered or certified mail with return
receipt requested, addressed as follows:


If to the Holder:
U.S. Telesource, Inc.
555 Seventeenth Street
Denver, Colorado 80202
Fax: 303-992-1724
Attention: Legal Counsel


If to the Company:

Critical Path, Inc.
320 First Street
San Francisco, California 94105
Fax: 415-808-8777
Attention: General Counsel

        Each of the foregoing parties shall be entitled to specify a different
address by giving five days' advance written notice as aforesaid to the other
parties. All such notices and communications shall be deemed to have been
received (i) in the case of personal delivery, on the date of such delivery and
(ii) in the case of mailing, on the third business day following the date of
such mailing.

                          SECTION 19 INVESTMENT INTENT

        By accepting this Warrant, the Holder represents that it is acquiring
this Warrant for investment and not with a view to, or for sale in connection
with, any distribution thereof.



                                      -9-
<PAGE>

        IN WITNESS WHEREOF, the Company has executed this Warrant as of the date
first written above.



CRITICAL PATH, INC.

By:
    -----------------------
    Brett Roberston
    Vice President of Strategic Development and
    General Counsel



ACCEPTED AND AGREED:

U.S. TELESOURCE, INC.

By:
    -------------------------------

Name: Marc B. Weisberg
      ----------------------------

Title: President and CEO
       ---------------------------

Date: 10/29/99
      ----------------------------




                                      -10-
<PAGE>

                               NOTICE OF EXERCISE

                             TO CRITICAL PATH, INC.


        The undersigned hereby irrevocably elects to exercise the Warrant
delivered herewith pursuant to Section 1.2 thereof as to __________ shares of
Common Stock and requests that certificates for such shares be issued in the
name of and delivered to the undersigned at the address stated below, and, if
additional shares remain available for purchase pursuant to the Warrant, the new
Warrant evidencing the right to purchase the balance of such shares shall be
registered in the name of, and delivered to, the undersigned at the address
stated below. The undersigned hereby agrees with and represents to the Company
that said shares of common stock are acquired for investment and not with a view
to, or for sale in connection with, any distribution or public offering thereof
within the meaning of the Securities Act of 1933, as amended, and agrees that
the exercise of the Warrant and the issuance and transfer of the common stock to
be purchased are subject to Sections 7 and 8 of the Warrant.

Payment is enclosed in the amount of $
                                      --------------------

Dated:
      --------------------------



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

By:
    ----------------------------

Its:
    ----------------------------



Address:

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

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

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

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



                                      -11-