VOTING AGREEMENT

Exhibit 99.1

VOTING AGREEMENT

BY AND AMONG

CP HOLDCO, LLC

AND

THE ENTITIES AND PERSONS NAMED ON SCHEDULE I HERETO

DATED AS OF DECEMBER 5, 2007

Table of Contents

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VOTING AGREEMENT

THIS VOTING AGREEMENT (this “ Agreement ”) is dated as of December 5, 2007, by and among CP Holdco, LLC, a Delaware limited liability company (“ Parent ”) and the entities and persons set forth on Schedule I attached hereto (each, a “ Shareholder ” and collectively, the “ Shareholders ”).

RECITALS

WHEREAS, concurrently with the execution of this Agreement, Parent, CP Merger Co., a California corporation and a wholly-owned subsidiary of Parent (“ Merger Sub ”, and, jointly with Parent, the “ Purchaser Parties ”) and Critical Path, Inc., a California corporation (the “ Company ”) have entered into that certain Agreement and Plan of Merger, dated as of the date hereof (as it may be amended, supplemented, modified from time to time, the “ Merger Agreement ”), which provides, among other things, for the merger of Merger Sub with and into the Company (the “ Merger ”) and certain other transactions contemplated therein, upon the terms and subject to the conditions set forth therein;

WHEREAS, in connection with the transactions contemplated by the Merger Agreement, the Company proposes to amend and restate its Articles of Incorporation (the “ Restated Articles ”);

WHEREAS, each Shareholder is the record and Beneficial Owner (as defined below) of, and has the sole right to vote and dispose of, that number of shares of (i) Common Stock, par value $0.001 per share, of the Company (the “ Common Stock ”), (ii) Series D Cumulative Redeemable Convertible Preferred Stock, par value $0.001 per share, of the Company (the “ Series D Preferred Stock ”) and/or (iii) Series E Redeemable Convertible Preferred Stock, par value $0.001 per share, of the Company (the “ Series E Preferred Stock ”), set forth next to such Shareholder’s name on Schedule II hereto; and

WHEREAS, as an inducement and condition to the Purchaser Parties entering into the Merger Agreement and incurring the obligations therein, the Purchaser Parties have required that each Shareholder enter into this Agreement and the Shareholders, as an inducement to the Purchaser Parties entering into the Merger Agreement and incurring the obligations therein, have agreed to enter into this Agreement.

NOW, THEREFORE, in consideration of the foregoing and the mutual covenants and agreements contained herein, the parties hereto, intending to be legally bound, agree as follows:

ARTICLE I

CERTAIN DEFINITIONS

Section 1.1 Capitalized Terms . Each capitalized term used in this Agreement and not defined herein shall have the meaning ascribed to such term in the Merger Agreement.

Section 1.2 Other Definitions . For the purposes of this Agreement:

(a) “ Agreement ” has the meaning set forth in the Preamble.

(b) “ Beneficial Owner ” or “ Beneficial Ownership ” with respect to any securities means having “beneficial ownership” of such securities (as determined pursuant to Rule 13d-3 under the Exchange Act).

(c) “ CK Shareholders ” means, collectively, those Shareholders set forth under the heading “CK Shareholders” in Schedule I hereto.

(d) “ Common Stock ” has the meaning set forth in the Recitals.

(e) “ Expiration Time ” has the meaning set forth in Section 2.1(a).

(f) “ GA Shareholders ” means, collectively, those Shareholders set forth under the heading “GA Shareholders” in Schedule I hereto.

(g) “ Legal Actions ” means any claims, actions, suits, demand letters, judicial, administrative or regulatory proceedings, or hearings, notices of violation, or investigations.

(h) “ Merger Agreement ” has the meaning set forth in the Recitals.

(i) “ Merger Sub ” has the meaning set forth in the Recitals.

(j) “ Owned Shares ” has the meaning set forth in Section 2.1(a).

(k) “ Parent ” has the meaning set forth in the Preamble.

(l) “ Permits ” means all authorizations, licenses, consents, certificates, registrations, approvals, orders and other permits of any Governmental Authority.

(m) “ Purchaser Parties ” has the meaning set forth in the Recital.

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(n) “ Representative ” means, with respect to any particular Person, any director, officer, employee, agent or other representative of such Person, including any consultant, accountant, legal counsel or investment banker.

(o) “ Restated Articles ” has the meaning set forth in the Recitals.

(p) “ Series D Preferred Stock ” has the meaning set forth in the Recitals.

(q) “ Series E Preferred Stock ” has the meaning set forth in the Recitals.

(r) “ Shareholder ” has the meaning set forth in the Preamble.

(s) “ Shares ” shall mean, for the purposes of this Agreement, all the shares of Common Stock, Series D Preferred Stock, Series E Preferred Stock and other voting securities into which such shares may be reclassified, sub-divided, consolidated or converted and any rights and benefits arising therefrom, including any dividends or distributions of securities which may be declared in respect of such shares and entitled to vote in respect of the matters contemplated by Article II and all other capital stock of the Company entitled to vote in respect of the matters contemplated by Article II.

(t) “ Shareholders’ Meeting ” has the meaning set forth in Section 2.1(a).

(u) “ Transfer ” means, with respect to a security, the sale, grant, assignment, transfer, pledge, encumbrance, hypothecation or other disposition of such security or the Beneficial Ownership thereof (including by operation of Law), or the entry into any Contract to effect any of the foregoing, including, for purposes of this Agreement, the transfer or sharing of any voting power of such security or other rights in or of such security, the granting of any proxy with respect to such security, depositing such security into a voting trust or entering into a voting agreement with respect to such security.

ARTICLE II

AGREEMENT TO VOTE

Section 2.1 Agreement to Vote .

(a) Subject to the terms and conditions hereof, each Shareholder, severally and not jointly, hereby irrevocably and unconditionally agrees that from and after the date hereof and until the earliest to occur of (i) the conversion, after the Reverse Split, of all then outstanding shares of Series D Preferred Stock and Series E Preferred Stock into shares of Common Stock, (ii) the termination of the Merger Agreement in accordance with its terms, and (iii) the written agreement of the Purchaser

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Parties, the GA Shareholders and the CK Shareholders to terminate this Agreement (such earliest occurrence being the “ Expiration Time ”), at any meeting (whether annual or special, and at each adjourned or postponed meeting) of the Company’s shareholders, however called, or in any other circumstances (including any action by written consent) upon which a vote or other consent or approval is sought (any such meeting or other circumstance, a “ Shareholders’ Meeting ”), each Shareholder will (x) appear at such a meeting or otherwise cause its Owned Shares to be counted as present thereat for purposes of calculating a quorum and respond to any other request by the Company for written consent, if any, and, unless otherwise expressly consented to in writing by the Purchaser Parties, in their sole discretion, and (y) vote, or cause to be voted, all of such Shareholder’s Shares Beneficially Owned by such Shareholder as of the relevant time (“ Owned Shares ”) (A) in favor of the adoption of the Merger Agreement (whether or not recommended by the Company Board of Directors or any committee thereof) and the approval of the transactions contemplated thereby, including the Merger, (B) in favor of the adoption of the Restated Articles (whether or not recommended by the Company’s Board of Directors or any committee thereof), and (C) in favor of the approval of any other matter to be approved by the shareholders of the Company to facilitate the transactions contemplated by the Merger Agreement and the filing of the Restated Articles. In addition, upon written notice from any GA Shareholder or any CK Shareholder that such GA Shareholder or CK Shareholder is electing to convert its shares of Series D Preferred Stock (if any) and Series E Preferred Stock into shares of Common Stock, each other Shareholder holding any shares of Series D Preferred Stock or Series E Preferred Stock shall immediately elect to convert all of its shares of Series D Preferred Stock and Series E Preferred Stock into shares of Common Stock pursuant to Section 7(aa) of Article V.C of the Restated Articles then in effect.

(b) Notwithstanding anything to the contrary contained in this Agreement, each of Peter Kellner, Richmond I, LLC, Richmond III, LLC, the Kellner Foundation, George Kellner, Trust FBO Peter and Catherine Kellner, Catherine Kellner, Clara Kellner and Paul Kellner (collectively, the “ Current Kellner Shareholders ”) and Richmond CP LLC (“ Richmond CP ”), hereby jointly and severally agree that (i) as soon as practicable after the date hereof (but in any event not more than five (5) days after the date hereof), each of the Current Kellner Shareholders shall assign, transfer, convey and deliver to Richmond CP, and Richmond CP shall accept the assignment and transfer from such Current Kellner Shareholder, all of the right, title and interest in and to (x) the Owned Shares of such Current Kellner Shareholder set forth opposite its name on Schedule II attached hereto and (y) all rights and obligations (including, without limitation, the obligation to vote its Owned Shares pursuant to the terms hereof) of such Current Kellner Shareholder pursuant to or arising out of this Agreement, and (ii) upon such assignment and transfer, Richmond CP hereby assumes and agrees to perform and discharge in full as and when due any and all liabilities and obligations of each of the Current Kellner Shareholders, of any type whatsoever, arising out of or relating to the Owned Shares or this Agreement, whether accruing before, on or after the date hereof. Upon the completion of such transfers pursuant to this Section 2.1(b), Schedule II hereto shall be amended in accordance with the provisions of Section 6.6.

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Section 2.2 Additional Shares . Each Shareholder, severally and not jointly, hereby agrees, while this Agreement is in effect, promptly to notify the Purchaser Parties of the number of any new Shares or equivalent thereof with respect to which Beneficial Ownership is acquired by such Shareholder, if any, after the date hereof and before the Expiration Time. Any such Shares shall automatically become subject to the terms of this Agreement as Owned Shares as though owned by such Shareholder as of the date hereof.

Section 2.3 Restrictions on Transfer, Etc . Except as provided for herein, each Shareholder, severally and not jointly, agrees, from the date hereof until the Expiration Time, not to (i) directly or indirectly Transfer, offer to Transfer or contract to Transfer any Owned Shares or Company Derivatives (other than (x) Transfers to Parent pursuant to that certain Conversion and Contribution Agreement, dated the date hereof, among Parent and the shareholders of the Company named therein and (y) Transfers by each Current Kellner Shareholder to Richmond CP pursuant to Section 2.1(b)); (ii) tender any Owned Shares or Company Derivatives into any tender or exchange offer; or (iii) otherwise restrict the ability of such Shareholder freely to exercise all voting rights with respect thereto. Any action attempted to be taken in violation of the preceding sentence shall be deemed null and void. Each Shareholder, severally and not jointly, further agrees to authorize and hereby authorizes the Purchaser Parties and the Company to notify the Company’s transfer agent and the Paying Agent that there is a stop transfer order with respect to all of the Owned Shares and that this Agreement places limits on the voting of the Owned Shares.

Section 2.4 Acknowledgement . Each Shareholder hereby acknowledges receipt and review of a copy of the Merger Agreement.

ARTICLE III

REPRESENTATIONS AND WARRANTIES OF SHAREHOLDERS

The Shareholders, severally and not jointly, represent and warrant to the Purchaser Parties as of the date of this Agreement and at all times during the term of this Agreement, as follows:

Section 3.1 Authority Relative to this Agreement . (i) Each Shareholder has the requisite capacity and authority to execute and deliver this Agreement, to fulfill and perform such Shareholder’s obligations hereunder and to consummate the transactions contemplated hereby and (ii) the execution and delivery of this Agreement by each Shareholder and the consummation by each Shareholder of the transactions to be consummated by it as contemplated hereby have been duly and validly executed and delivered by such Shareholder and, assuming the due authorization, execution and delivery by Parent, constitutes a legal, valid and binding agreement of such Shareholder enforceable by the Purchaser Parties against such Shareholder in accordance with its terms and no other proceedings on the part of such Shareholder are necessary to authorize this Agreement, to perform such obligations or to consummate such transactions.

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Section 3.2 No Conflict . Other than the filing by a Shareholder of any reports with the SEC required by Sections 13(d) or 16(a) of the Exchange Act, none of the execution and delivery of this Agreement by a Shareholder, the consummation by a Shareholder of the transactions contemplated hereby or compliance by a Shareholder with any of the provisions her