ZIXI Zix Corp

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

(RULE 14d-100)

Tender Offer Statement Pursuant to Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

(Amendment No. 4)

Zix Corporation

(Name of Subject Company)

Zeta Merger Sub Inc.

(Offeror)

Open Text Corporation

(Parent of Offeror)

(Names of Filing Persons)

COMMON STOCK, PAR VALUE $0.01 PER SHARE

(Title of Class of Securities)

98974P100

(CUSIP Number of Class of Securities)

Gordon A. Davies

Open Text Corporation

Executive Vice President, Chief Legal Officer and Corporate Development

275 Frank Tompa Drive, Waterloo, Ontario, Canada N2L 0A1

519-888-7111

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications on Behalf of Filing Persons)

Copies to:

James E. Langston

Aaron J. Meyers

Cleary Gottlieb Steen & Hamilton LLP

One Liberty Plaza

New York, New York 10006

212-225-2000

CALCULATION OF FILING FEE

Check the appropriate boxes below to designate any transactions to which the statement relates:

Check the following box if the filing is a final amendment reporting the results of the tender offer. ☒

If applicable, check the appropriate box(es) below to designate the appropriate rule provision(s) relied upon:

This Amendment No. 4 (this “Amendment”) amends and supplements the Tender Offer Statement on Schedule TO, as amended and supplemented by Amendment No. 1 filed on December 8, 2021, Amendment No. 2 filed on December 14, 2021, and Amendment No. 3 filed on December 21, 2021 filed by Zeta Merger Sub Inc., a Texas corporation (“Purchaser”) that is a wholly-owned subsidiary of Open Text Corporation, a corporation incorporated under the federal laws of Canada (“OpenText”), with the Securities and Exchange Commission on November 22, 2021 (together with any subsequent amendments and supplements thereto, including this Amendment, the “Schedule TO”). The Schedule TO relates to the tender offer by Purchaser for all shares of common stock of Zix Corporation, a Texas corporation (“Zix”), par value $0.01 per share (each, a “Share”), that are issued and outstanding, at a price of $8.50 per Share, in cash, without interest and subject to any applicable withholding of taxes, upon the terms and subject to the conditions set forth in the Offer to Purchase dated November 22, 2021 (the “Offer to Purchase”), a copy of which is attached to the Schedule TO as Exhibit (a)(1)(A), and in the related letter of transmittal (the “Letter of Transmittal”), a copy of which is attached to the Schedule TO as Exhibit (a)(1)(B) (and which, together with the Offer to Purchase and other related materials, as each may be amended or supplemented from time to time, collectively constitute the “Offer”).

All capitalized terms used but not defined in this Amendment No. 4 shall have the meanings assigned to such terms in the Schedule TO.

The items of the Schedule TO set forth below are hereby amended and supplemented as follows:

Amendments to the Schedule TO

The Offer to Purchase and Items 1-9 and 11 of the Schedule TO are hereby amended and supplemented by adding the following paragraphs at the end thereof:

“Consummation of the Offer and the Merger.

On Thursday, December 23, 2021, OpenText announced the expiration of the Offer at one minute after 11:59 P.M., Eastern time on December 22, 2021. The Depositary for the Offer has advised OpenText and Purchaser that immediately prior to the Expiration Time on Wednesday, December 22, 2021, there were validly tendered and not withdrawn (and excluding any Shares tendered pursuant to guaranteed delivery procedures that were not yet delivered in satisfaction of such guarantee in accordance with Section 21.459(c) of the TBOC)), a total of 55,709,092 Shares. The validly tendered Shares represent approximately 71% of the Shares outstanding immediately prior to the Expiration Time. The number of Shares tendered into the Offer satisfied the Minimum Condition immediately prior to the Expiration Time. All conditions to the Offer have been satisfied. Purchaser has accepted for payment all Shares that were validly tendered pursuant to the Offer and not withdrawn prior to the Expiration Time.

On December 23, 2021, following the expiration of the Offer and acceptance for payment of the Shares tendered pursuant to the Offer, OpenText completed its acquisition of Zix pursuant to the terms of the Merger Agreement. Pursuant to the terms and conditions of the Merger Agreement, Purchaser merged with and into Zix, with Zix surviving the Merger as a wholly-owned subsidiary of OpenText, without a stockholder vote to adopt the Merger Agreement or effect the Merger in accordance with Section 21.459(c) of the TBOC. As a result of the Merger, each Share outstanding immediately prior to the Effective Time was converted into the right to receive the Merger Consideration in cash, without interest, and subject to any applicable withholding of taxes (which is the same amount per Share that will be paid in the Offer), other than Shares held by OpenText or Zix, or by any wholly-owned subsidiary of OpenText (including Purchaser) or Zix, or held by stockholders who properly exercised appraisal rights under Subchapter H, Chapter 10 of the TBOC or Shares irrevocably accepted for purchase pursuant to the Offer.

As a result of the Merger, the Shares will be delisted and will cease trading on the Nasdaq. OpenText and Purchaser intend to take steps to cause the termination of the registration of the Shares under the Exchange Act and to suspend all of Zix’s reporting obligations under the Exchange Act as promptly as practicable.

The full text of the press release issued by OpenText on December 23, 2021 in connection with the expiration of the Offer and the Merger is attached hereto as Exhibit (a)(5)(N) and is incorporated herein by reference.”

Item 12. Exhibits.

Item 12 of the Schedule TO is hereby amended and supplemented with the following:

SIGNATURE

After due inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: December 23, 2021

EXHIBIT INDEX