UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the Securities

Securities Exchange Act of 1934

(Amendment (Amendment No.                )

Filed by the Registrant   ☒                            Filed by a Party other than the Registrant  ☐

Check the appropriate box:

ZIX CORPORATION

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

ZIX CORPORATION

2711 North Haskell Avenue

Suite 2200,2300, LB 36,

Dallas, Texas 75204-2960

To our Shareholders,

You are cordially invited to attend the Annual Meeting of Shareholders of Zix Corporation, which will take place Wednesday, June 5, 2019,9, 2021, at 10:00 a.m. Central Time atTime. The Annual Meeting will be a virtual meeting held over the Cityplace Conference Center, Turtle Creek I Room, 2711 North Haskell Avenue, Dallas, Texas 75204.Internet. You will be able to attend the virtual Annual Meeting, vote your shares electronically, and submit your questions during the live audio-only webcast of the virtual Annual Meeting by visiting www.virtualshareholdermeeting.com/ZIXI2021 and entering your control number contained on your proxy card. Details of the business to be conducted at the Annual Meeting are given in the Official Notice of the Meeting, Proxy Statement and form of proxy that accompany this letter.

Even ifRegardless of whether you intendplan to join us in person,attend the virtual Annual Meeting, we encourage you to vote in advance so that we will know that we have a quorum of shareholders entitled to vote at the meeting. When you vote in advance, please indicate your intention to personally attend the virtual Annual Meeting. Please see the Question and Answer section of the enclosed Proxy Statement for instructions if you plan to personally attend the virtual Annual Meeting.

Whether or not you are able to personally attend the virtual Annual Meeting, it is important that your shares be represented and voted. Your prompt vote over the Internet, by telephone via toll-free number, or by written proxy will save us the expense and extra work of additional proxy solicitation. Voting by any of these methods at your earliest convenience will ensure your representation at the Annual Meeting if you choose not to attend in person.the virtual Annual Meeting. If you decide to attend the virtual Annual Meeting, you will be able to vote in person,electronically, even if you have personally submitted your proxy. Please review the instructions on the proxy card or the information forwarded by your bank, broker, or other holder of record concerning each of these voting options.

We appreciate your continued interest in Zix Corporation.

						On behalf of the Board of Directors,
Dallas, Texas		Robert C. Hausmann
April 23, 2021				Robert C. Hausmann
April 26, 2019						ChairmanChair of the Board

ZIX CORPORATION

2711 North Haskell Avenue

Suite 2200,2300, LB 36

Dallas, Texas 75204-2960

NOTICE OF ANNUAL MEETING OF SHAREHOLDERS

The Annual Meeting of Shareholders of Zix Corporation will take place on Wednesday, June 5, 2019,9, 2021, at 10:00 a.m. Central Time atTime. The Annual Meeting will be a virtual meeting held entirely online. You will be able to attend the Cityplace Conference Center, Turtle Creek I Room, 2711 North Haskell Avenue, Dallas, Texas 75204. Registration will begin at 9:30 a.m.virtual Annual Meeting, vote your shares electronically, and submit your questions during the live audio-only webcast of the virtual Annual Meeting by visiting www.virtualshareholdermeeting.com/ZIXI2021 and entering your control number contained on your proxy card.

At the meeting,virtual Annual Meeting, we will ask shareholders entitled to vote to consider and vote on the following proposals:

Only shareholders of record of our common stock and our Series A Preferred Stock at the close of business on April 12, 20192021 will be entitled to vote at the meeting. Our stock transfer books will not be closed.

						By Order of the Board of Directors,
Dallas, Texas		Noah F. Webster
April 23, 2021				Noah F. Webster
April 26, 2019						General CounselChief Legal & Compliance Officer and Corporate Secretary

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS

FOR THE SHAREHOLDER MEETING TO BE HELD ON JUNE 5, 20199, 2021

This Proxy Statement, accompanying proxy card and our Annual Report are available at investor.zixcorp.com in a searchable, readable, and printable format and in a cookie-free environment.

YOUR VOTE IS IMPORTANT.

Whether or not you expect to personally attend the virtual meeting, we urge you to vote your shares at your earliest convenience to ensure the presence of a quorum at the meeting. Promptly voting your shares via the Internet, by telephone via toll-free number, or if you received a paper copy of the proxy card, by signing, dating, and returning the proxy card in the enclosed postage-paid envelope will save us the expense and extra work of additional solicitation. Because your proxy is revocable at your option, submitting your proxy now will not prevent you from voting your shares at the virtual meeting if you desire to do so. Please refer to the voting instructions included on your proxy card or the voting instructions forwarded by your bank, broker, or other holder of record.

TABLE OF CONTENTS

Questions and Answers About the Annual Meeting and Voting

This Question and Answer section provides some background information and brief answers to several questions you might have about the enclosed proposals. We encourage you to read this Proxy Statement in its entirety.

What is a proxy?

A proxy is your legal designation of another person, called a proxy holder, to vote the shares that you own. If you designate someone as your proxy holder in a written document, that document is called a proxy.

When I vote my shares, whom am I designating as my proxy?

We have designated Noah F. Webster, our General CounselChief Legal & Compliance Officer and Corporate Secretary, and David E. Rockvam, our Chief Financial Officer, to act as proxy holders at the Annual Meeting as to all shares for which proxy cards are returned or voting instructions are provided by Internet or telephonic voting.

What is a proxy statement?

A proxy statement is a document that the Securities and Exchange Commission (the “SEC”) regulations require us to give you when we ask you to sign a proxy card designating the proxy holders described above to vote on your behalf.

What is the record date?

The record date for the Annual Meeting is April 12, 2019.2021. The record date is established by our Board of Directors as required by Texas law. Only shareholders of record of our common stock and our Series A Preferred Stock (collectively, our “Voting Shareholders”) at the close of business on the record date are entitled to receive notice of the Annual Meeting and to vote their shares atelectronically during the meeting.live audio-only webcast of the Annual Meeting, or by telephone from the U.S. using the toll-free telephone number on the proxy card, or by the Internet, using the procedures and instructions described on the proxy card and other enclosures.

What is the difference between a shareholder of record and a shareholder who holds stock in street name, also called a “beneficial owner”?

If your shares are registered in your name at our stock registrar and transfer agent, Computershare Trust Company, N.A., you are a shareholder of record.

If your shares are registered at our stock registrar and transfer agent, Computershare Trust Company, N.A., in the name of a broker, bank, trustee, nominee, or other similar shareholder of record, your shares are held in street name and you are the beneficial owner of the shares.

What methods can I use to vote?

By Written Proxy.All Voting Shareholders may vote by mailing the written proxy card.

By Telephone and Internet Proxy.All Voting Shareholders of record may vote by telephone from the U.S. using the toll-free telephone number on the proxy card, or by the Internet, using the procedures and instructions described on the proxy card and other enclosures. Street name holders may vote by telephone or the Internet if their bank, broker, or other Voting Shareholder of record makes those methods available, in which case the bank, broker, or other Voting Shareholder of record will enclose the instructions with the Proxy Statement. The telephone and Internet voting procedures, including the use of control numbers, are designed to authenticate Voting Shareholders’ identities, to allow Voting Shareholders to vote their shares, and to confirm that their instructions have been properly recorded.

ByIn- Person Ballot Electronic Submission during the Virtual Annual Meeting. Voting Shareholders of record and street name holders may vote in person atelectronically during the live audio-only webcast of the Annual Meeting as described in the following question and answer.

-i-i

How do I cast aan electronic ballot in person atduring the live audio-only webcast of the Annual Meeting?

Voting

ZIX CORPORATION

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

ZIX CORPORATION

2711 North Haskell Avenue

Suite 2300, LB 36, Dallas, Texas 75204-2960

To our Shareholders,

You are cordially invited to attend the Annual Meeting of Shareholders of Record.Zix Corporation, which will take place Wednesday, June 9, 2021, at 10:00 a.m. Central Time. The Annual Meeting will be a virtual meeting held over the Internet. You will needbe able to bring a government-issued photo identification cardattend the virtual Annual Meeting, vote your shares electronically, and submit your questions during the live audio-only webcast of the virtual Annual Meeting by visiting www.virtualshareholdermeeting.com/ZIXI2021 and entering your control number contained on your proxy card. Details of the business to obtain a ballotbe conducted at the Annual Meeting are given in the Official Notice of the Meeting, Proxy Statement and form of proxy that accompany this letter.

Regardless of whether you plan to attend the virtual Annual Meeting, we encourage you to vote in personadvance so that we will know that we have a quorum of shareholders entitled to vote at the meeting. When you vote in advance, please indicate your intention to attend the virtual Annual Meeting. Please see the Question and Answer section of the enclosed Proxy Statement for instructions if you plan to attend the virtual Annual Meeting.

Whether or not you are able to attend the virtual Annual Meeting, it is important that your shares be represented and voted. Your prompt vote over the Internet, by telephone via toll-free number, or by written proxy will save us the expense and extra work of additional proxy solicitation. Voting by any of these methods at your earliest convenience will ensure your representation at the Annual Meeting if you choose not to attend the virtual Annual Meeting. If you decide to attend the virtual Annual Meeting, you will be able to vote electronically, even if you have personally submitted your proxy. Please review the instructions on the proxy card or the information forwarded by your bank, broker, or other holder of record concerning each of these voting options.

Street Name Holders.We appreciate your continued interest in Zix Corporation.

ZIX CORPORATION

2711 North Haskell Avenue

Suite 2300, LB 36

Dallas, Texas 75204-2960

NOTICE OF ANNUAL MEETING OF SHAREHOLDERS

The Annual Meeting of Shareholders of Zix Corporation will take place on Wednesday, June 9, 2021, at 10:00 a.m. Central Time. The Annual Meeting will be a virtual meeting held entirely online. You will needbe able to attend the virtual Annual Meeting, vote your shares electronically, and submit your questions during the live audio-only webcast of the virtual Annual Meeting by visiting www.virtualshareholdermeeting.com/ZIXI2021 and entering your control number contained on your proxy card.

At the virtual Annual Meeting, we will ask your broker or bank for a legal proxyshareholders entitled to vote to consider and youvote on the following proposals:

Only shareholders of record of our common stock and our Series A Preferred Stock at the close of business on April 12, 2021 will needbe entitled to bring the legal proxy with you tovote at the meeting. YouOur stock transfer books will not be ableclosed.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS

FOR THE SHAREHOLDER MEETING TO BE HELD ON JUNE 9, 2021

This Proxy Statement, accompanying proxy card and our Annual Report are available at investor.zixcorp.com in a searchable, readable, and printable format and in a cookie-free environment.

YOUR VOTE IS IMPORTANT.

Whether or not you expect to attend the virtual meeting, we urge you to vote your shares at your earliest convenience to ensure the presence of a quorum at the meeting. Promptly voting your shares via the Internet, by telephone via toll-free number, or if you received a paper copy of the proxy card, by signing, dating, and returning the proxy card in the enclosed postage-paid envelope will save us the expense and extra work of additional solicitation. Because your proxy is revocable at your option, submitting your proxy now will not prevent you from voting your shares at the virtual meeting withoutif you desire to do so. Please refer to the voting instructions included on your proxy card or the voting instructions forwarded by your bank, broker, or other holder of record.

TABLE OF CONTENTS

Questions and Answers About the Annual Meeting and Voting

This Question and Answer section provides some background information and brief answers to several questions you might have about the enclosed proposals. We encourage you to read this Proxy Statement in its entirety.

What is a proxy?

A proxy is your legal proxy. You will also need to bringdesignation of another person, called a government-issued photo identification card to obtain a ballotproxy holder, to vote the shares that you own. If you designate someone as your proxy holder in persona written document, that document is called a proxy.

When I vote my shares, whom am I designating as my proxy?

We have designated Noah F. Webster, our Chief Legal & Compliance Officer and Corporate Secretary, and David E. Rockvam, our Chief Financial Officer, to act as proxy holders at the Annual Meeting. Please noteMeeting as to all shares for which proxy cards are returned or voting instructions are provided by Internet or telephonic voting.

What is a proxy statement?

A proxy statement is a document that ifthe Securities and Exchange Commission (the “SEC”) regulations require us to give you ownwhen we ask you to sign a proxy card designating the proxy holders described above to vote on your behalf.

What is the record date?

The record date for the Annual Meeting is April 12, 2021. The record date is established by our Board of Directors as required by Texas law. Only shareholders of record of our common stock and our Series A Preferred Stock (collectively, our “Voting Shareholders”) at the close of business on the record date are entitled to receive notice of the Annual Meeting and to vote their shares electronically during the live audio-only webcast of the Annual Meeting, or by telephone from the U.S. using the toll-free telephone number on the proxy card, or by the Internet, using the procedures and instructions described on the proxy card and other enclosures.

What is the difference between a shareholder of record and a shareholder who holds stock in street name, also called a “beneficial owner”?

If your shares are registered in your name at our stock registrar and transfer agent, Computershare Trust Company, N.A., you are a shareholder of record.

If your shares are registered at our stock registrar and transfer agent, Computershare Trust Company, N.A., in the name of a broker, bank, trustee, nominee, or other similar shareholder of record, your shares are held in street name and you are issued a legal proxy, any previously executed proxy will be revoked and your vote will not be counted unless you appear at the meeting and vote in person.beneficial owner of the shares.

What methods can I use to vote?

By Written Proxy. All Voting Shareholders may vote by mailing the written proxy card.

By Telephone and Internet Proxy. All Voting Shareholders of record may vote by telephone from the U.S. using the toll-free telephone number on the proxy card, or by the Internet, using the procedures and instructions described on the proxy card and other enclosures. Street name holders may vote by telephone or the Internet if their bank, broker, or other Voting Shareholder of record makes those methods available, in which case the bank, broker, or other Voting Shareholder of record will occur atenclose the instructions with the Proxy Statement. The telephone and Internet voting procedures, including the use of control numbers, are designed to authenticate Voting Shareholders’ identities, to allow Voting Shareholders to vote their shares, and to confirm that their instructions have been properly recorded.

By Electronic Submission during the Virtual Annual Meeting?

First, we will determine whether we have a quorumMeeting. Voting Shareholders of shares represented atrecord and street name holders may vote electronically during the live audio-only webcast of the Annual Meeting to conduct business. If a quorum is not present at the Annual Meeting, we will adjourn or reschedule the meeting. If enough shares are represented at the Annual Meeting to conduct business, then we will vote on the proposalsas described in this Proxy Statementthe following question and any other business properly brought before the meeting or any adjournment or postponement thereof. We know of no other matters that will be presented for consideration at the Annual Meeting. If, however, other matters or proposals are presented and properly come before the meeting, the proxy holders intend to vote all proxies in accordance with their best judgment in the interest of Zix Corporation and our shareholders.

A representative of Whitley Penn LLP, our independent registered public accounting firm, is expected to be present at the Annual Meeting and will be afforded the opportunity to make a statement, if that representative so desires, and to respond to appropriate questions. A representative of Broadridge Financial Solutions, Inc. will count the votes and act as the independent inspector of election.

What is a quorum?

The holders of a majority of the shares entitled to vote at the Annual Meeting must be represented at the meeting in person or by proxy to have a quorum for the transaction of business at the meeting and to act on the matters specified in the notice. A Voting Shareholder will be deemed to be represented at the Annual Meeting if such shareholder:

As of the record date, there were 55,596,180 shares of common stock outstanding and entitled to vote at the Annual Meeting, held by or through 420 holders of record. Each share of our common stock is entitled to one vote.

As of the record date, 64,914 shares of our Series A Preferred Stock were outstanding and entitled to vote on anas-converted basis at the Annual Meeting, held by or through one holder of record. As of the record date, the 64,914 shares of Series A Preferred Stock were convertible into 10,910,124 shares of our common stock. However, under applicable Nasdaq Listing Rules, the number of shares of common stock into which the Series A Preferred Stock can be converted, when aggregated with any other common stock held by such holder, cannot exceed 19.9% of the number of shares of our common stock outstanding as of February 20, 2019, immediately prior to the issuance of the Series A Preferred Stock. Additionally, under applicable Nasdaq Listing Rules, the number of votes that a holder of Series A Preferred Stock will be entitled to cast on any matter to be voted upon, when aggregated with any of our other voting securities held by such holder, cannot exceed 19.9% of the number of our voting securities outstanding as of February 20, 2019, immediately prior to the issuance of the Series A Preferred Stock. For the one record holder of our Series Aanswer.

-ii-

How often willdo I cast an electronic ballot during the Company hold an advisory vote to approve executive compensation?

At our 2017 Annual Meeting of Shareholders, our shareholders voted, in an advisory vote, on various frequencies for conducting future advisory votes with respect to compensation of our named executive officers, with an annual frequency receiving the most advisory votes that were cast. After considering those voting results and other factors, our Board determined that the Company would hold an annual advisory vote on the compensation of our named executive officers until (a) the next required vote on the frequency of shareholder votes on the compensation of our named executive officers or (b) the Board otherwise determines that a different frequency for such advisory votes is in the best interests of our shareholders.

What are my voting choices on Proposal 4, the approval of the Nasdaq Proposal?

For the vote on the approval of the Nasdaq Proposal, Voting Shareholders (other than the holder of the shares of Series A Preferred Stock purchased in the private placement on February 20, 2019) may:

Our Board recommends that you vote “FOR” Proposal 4.

What vote is required for the approval of the Nasdaq Proposal?

Under Nasdaq Listing Rules, approval of the Nasdaq Proposal requires the FOR vote of a majority of the votes cast (either FOR or AGAINST) on the Nasdaq Proposal. Our bylaws require the FOR vote of the holders of a majority of the shares entitled to vote on the Nasdaq Proposal and represented in person or by proxy at the Annual Meeting. In order to satisfy both the Nasdaq Listing Rules and our bylaws, approval of the Nasdaq Proposal will require the FOR vote of the holders of a majority of the shares entitled to vote on the Nasdaq Proposal and represented in person or by proxy at the Annual Meeting. Because votes to ABSTAIN are counted as shares entitled to vote on the Nasdaq Proposal, they will have the same effect as votes AGAINST the Nasdaq Proposal.

In accordance with applicable Nasdaq Listing Rules, the holder of the shares of Series A Preferred Stock purchased in the private placement on February 20, 2019 is not entitled to vote such shares on the Nasdaq Proposal.

Holders of our Series B Preferred Stock are not entitled to vote on any matters at the Annual Meeting.

What if a Voting Shareholder does not specify a choice for a matter when returning a proxy?

Voting Shareholders should specify their choice for each proposal described on the enclosed proxy card. Proxy cards that are signed and returned will be voted FOR proposals described in this proxy statement for which no specific instructions are given.

How are withheld votes, abstentions and brokernon-votes counted?

Both abstentions and brokernon-votes are counted as “present” for purposes of determining the existence of a quorum at the Annual Meeting. Shares voted WITHHELD as to a director nominee on Proposal 1 will have no effect on the election of the nominees, but, for purposes of the Majority WITHHELD Vote and the effectiveness of a nominee’s conditional resignation, will count as votes against the indicated nominee. Shares voted ABSTAIN on Proposals 2, 3 and 4 will have the same effect as votes cast AGAINST that proposal. Brokernon-votes will not be included in vote totals and will not affect the outcome of the vote on the proposals.

-v-

ZIX CORPORATION

2711 North Haskell Avenue

Suite 2200,2300, LB 36, Dallas, Texas 75204-2960

To our Shareholders,

You are cordially invited to attend the Annual Meeting of Shareholders of Zix Corporation, which will take place Wednesday, June 9, 2021, at 10:00 a.m. Central Time. The Annual Meeting will be a virtual meeting held over the Internet. You will be able to attend the virtual Annual Meeting, vote your shares electronically, and submit your questions during the live audio-only webcast of the virtual Annual Meeting by visiting www.virtualshareholdermeeting.com/ZIXI2021 and entering your control number contained on your proxy card. Details of the business to be conducted at the Annual Meeting are given in the Official Notice of the Meeting, Proxy Statement and form of proxy that accompany this letter.

Regardless of whether you plan to attend the virtual Annual Meeting, we encourage you to vote in advance so that we will know that we have a quorum of shareholders entitled to vote at the meeting. When you vote in advance, please indicate your intention to attend the virtual Annual Meeting. Please see the Question and Answer section of the enclosed Proxy Statement for instructions if you plan to attend the virtual Annual Meeting.

Whether or not you are able to attend the virtual Annual Meeting, it is important that your shares be represented and voted. Your prompt vote over the Internet, by telephone via toll-free number, or by written proxy will save us the expense and extra work of additional proxy solicitation. Voting by any of these methods at your earliest convenience will ensure your representation at the Annual Meeting if you choose not to attend the virtual Annual Meeting. If you decide to attend the virtual Annual Meeting, you will be able to vote electronically, even if you have personally submitted your proxy. Please review the instructions on the proxy card or the information forwarded by your bank, broker, or other holder of record concerning each of these voting options.

We appreciate your continued interest in Zix Corporation.

ZIX CORPORATION

2711 North Haskell Avenue

Suite 2300, LB 36

Dallas, Texas 75204-2960

NOTICE OF ANNUAL MEETING OF SHAREHOLDERS

The Annual Meeting of Shareholders of Zix Corporation will take place on Wednesday, June 9, 2021, at 10:00 a.m. Central Time. The Annual Meeting will be a virtual meeting held entirely online. You will be able to attend the virtual Annual Meeting, vote your shares electronically, and submit your questions during the live audio-only webcast of the virtual Annual Meeting by visiting www.virtualshareholdermeeting.com/ZIXI2021 and entering your control number contained on your proxy card.

At the virtual Annual Meeting, we will ask shareholders entitled to vote to consider and vote on the following proposals:

Only shareholders of record of our common stock and our Series A Preferred Stock at the close of business on April 12, 2021 will be entitled to vote at the meeting. Our stock transfer books will not be closed.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS

FOR THE SHAREHOLDER MEETING TO BE HELD ON JUNE 9, 2021

This Proxy Statement, accompanying proxy card and our Annual Report are available at investor.zixcorp.com in a searchable, readable, and printable format and in a cookie-free environment.

YOUR VOTE IS IMPORTANT.

Whether or not you expect to attend the virtual meeting, we urge you to vote your shares at your earliest convenience to ensure the presence of a quorum at the meeting. Promptly voting your shares via the Internet, by telephone via toll-free number, or if you received a paper copy of the proxy card, by signing, dating, and returning the proxy card in the enclosed postage-paid envelope will save us the expense and extra work of additional solicitation. Because your proxy is revocable at your option, submitting your proxy now will not prevent you from voting your shares at the virtual meeting if you desire to do so. Please refer to the voting instructions included on your proxy card or the voting instructions forwarded by your bank, broker, or other holder of record.

TABLE OF CONTENTS

Questions and Answers About the Annual Meeting and Voting

This Question and Answer section provides some background information and brief answers to several questions you might have about the enclosed proposals. We encourage you to read this Proxy Statement in its entirety.

What is a proxy?

A proxy is your legal designation of another person, called a proxy holder, to vote the shares that you own. If you designate someone as your proxy holder in a written document, that document is called a proxy.

When I vote my shares, whom am I designating as my proxy?

We have designated Noah F. Webster, our Chief Legal & Compliance Officer and Corporate Secretary, and David E. Rockvam, our Chief Financial Officer, to act as proxy holders at the Annual Meeting as to all shares for which proxy cards are returned or voting instructions are provided by Internet or telephonic voting.

What is a proxy statement?

A proxy statement is a document that the Securities and Exchange Commission (the “SEC”) regulations require us to give you when we ask you to sign a proxy card designating the proxy holders described above to vote on your behalf.

What is the record date?

The record date for the Annual Meeting is April 12, 2021. The record date is established by our Board of Directors as required by Texas law. Only shareholders of record of our common stock and our Series A Preferred Stock (collectively, our “Voting Shareholders”) at the close of business on the record date are entitled to receive notice of the Annual Meeting and to vote their shares electronically during the live audio-only webcast of the Annual Meeting, or by telephone from the U.S. using the toll-free telephone number on the proxy card, or by the Internet, using the procedures and instructions described on the proxy card and other enclosures.

What is the difference between a shareholder of record and a shareholder who holds stock in street name, also called a “beneficial owner”?

If your shares are registered in your name at our stock registrar and transfer agent, Computershare Trust Company, N.A., you are a shareholder of record.

If your shares are registered at our stock registrar and transfer agent, Computershare Trust Company, N.A., in the name of a broker, bank, trustee, nominee, or other similar shareholder of record, your shares are held in street name and you are the beneficial owner of the shares.

What methods can I use to vote?

By Written Proxy. All Voting Shareholders may vote by mailing the written proxy card.

By Telephone and Internet Proxy. All Voting Shareholders of record may vote by telephone from the U.S. using the toll-free telephone number on the proxy card, or by the Internet, using the procedures and instructions described on the proxy card and other enclosures. Street name holders may vote by telephone or the Internet if their bank, broker, or other Voting Shareholder of record makes those methods available, in which case the bank, broker, or other Voting Shareholder of record will enclose the instructions with the Proxy Statement. The telephone and Internet voting procedures, including the use of control numbers, are designed to authenticate Voting Shareholders’ identities, to allow Voting Shareholders to vote their shares, and to confirm that their instructions have been properly recorded.

By Electronic Submission during the Virtual Annual Meeting. Voting Shareholders of record and street name holders may vote electronically during the live audio-only webcast of the Annual Meeting as described in the following question and answer.

i

How do I cast an electronic ballot during the live audio-only webcast of the Annual Meeting?

Voting Shareholders of Record. To log in to the Annual Meeting and to cast your vote electronically during the virtual meeting, you will need the unique control number which appears on the notice regarding the availability of proxy materials, the proxy card (printed in the box and marked by the arrow) and the instructions that accompanied the proxy materials.

Street Name Holders. To log in to the Annual Meeting and to cast your vote electronically during the virtual meeting, you will need to ask your broker or bank for a control number and your broker or bank will provide you with instructions that you must follow to have your shares voted. Please note that if you own shares in street name and you are issued a legal proxy, any previously executed proxy will be revoked and your vote will not be counted unless you attend the virtual meeting and vote your shares electronically.

What will occur at the Annual Meeting?

First, we will determine whether we have a quorum of shares represented at the Annual Meeting to conduct business. If a quorum is not present at the Annual Meeting, we will adjourn or reschedule the meeting. If enough shares are represented at the Annual Meeting to conduct business, then we will vote on the proposals described in this Proxy Statement and any other business properly brought before the meeting or any adjournment or postponement thereof. We know of no other matters that will be presented for consideration at the Annual Meeting. If, however, other matters or proposals are presented and properly come before the meeting, the proxy holders intend to vote all proxies in accordance with their best judgment in the interest of Zix Corporation and our shareholders.

A representative of Whitley Penn LLP, our independent registered public accounting firm, is expected to be virtually present at the Annual Meeting and will be afforded the opportunity to make a statement, if that representative so desires, and to respond to appropriate questions. A representative of Broadridge Financial Solutions, Inc. will count the votes and act as the independent inspector of election.

What is a quorum?

The holders of a majority of the shares entitled to vote at the Annual Meeting must be represented at the virtual meeting in person or by proxy to have a quorum for the transaction of business at the meeting and to act on the matters specified in the notice. A Voting Shareholder will be deemed to be represented at the virtual Annual Meeting if such shareholder:

As of the record date, there were 57,058,008 shares of common stock outstanding and entitled to vote at the Annual Meeting, held by or through385 holders of record. Each share of our common stock is entitled to one vote.

As of the record date, 100,206 shares of our Series A Preferred Stock were outstanding and entitled to vote on an as-converted basis at the Annual Meeting, held by or through one holder of record. As of the record date, the 100,206 shares of Series A Preferred Stock were convertible into 19,733,971 shares of our common stock.

Our Voting Shareholders are entitled to cast an aggregate of 76,791,979 votes at the Annual Meeting, so a quorum equals 38,395,991 shares of our common stock (in each case, including the Series A Preferred Stock on an as-converted basis).

As of the record date, there were no shares of our Series B Preferred Stock outstanding.

ii

What proposals are Voting Shareholders being asked to consider at the Annual Meeting?

At the Annual Meeting, we will ask our Voting Shareholders to consider and vote on the following:

What are my voting choices on Proposal 1 for director nominees?

For the vote on the election of the director nominees, Voting Shareholders may:

The Board recommends that you vote “FOR” Proposal 1 and “FOR” each of the director nominees.

What vote is needed to elect directors?

The eight nominees will be elected who receive a plurality of the FOR votes out of all votes cast (either FOR or WITHHELD) electronically during the live audio-only webcast or by proxy at the Annual Meeting.

What is a plurality of the votes?

In order to be elected, a director nominee does not have to receive a majority of FOR votes cast out of all votes cast either affirmatively or withheld electronically during the live audio-only webcast or by proxy at the Annual Meeting. Instead, the eight nominees who will be elected are those who receive the most FOR votes of all the votes cast on Proposal 1 electronically during the live audio-only webcast or by proxy at the meeting.

What happens if a director nominee does not receive a majority of FOR votes?

Under our Director Nomination and Election Policies, each director nominee in an uncontested election tenders his or her conditional resignation to the Corporate Secretary before the Annual Meeting. That resignation offer becomes effective automatically if the tendering director nominee fails to receive a majority of FOR votes cast out of all votes cast either affirmatively or withheld electronically during the live audio-only webcast or by proxy at the Annual Meeting (“Majority WITHHELD Vote”). The Nominating and Corporate Governance Committee of the Board (the “Nominating and Corporate Governance Committee”) then recommends to the Board whether to accept the offered resignation. The Board will, within 90 days after the certification of voting results, decide whether or not to accept the offered resignation. In general, any director nominee who receives a Majority WITHHELD Vote will not participate in the Nominating and Corporate Governance Committee recommendation or the Board decision regarding an offered resignation. If all members of the Nominating and Corporate Governance Committee received a Majority WITHHELD Vote, then the independent directors who did not receive a Majority WITHHELD Vote will appoint a committee among themselves to consider and make a recommendation to the Board with respect to the offered resignations. If three or fewer directors receive a majority of FOR votes cast out of all votes cast either affirmatively or withheld electronically during the live audio-only webcast or by proxy at the Annual Meeting, then all directors (including those who received a Majority WITHHELD Vote) may participate in the Board’s decision whether to accept or not to accept the

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offered resignations. The Company will promptly disclose the Board’s decision in a Current Report on Form 8-K, including the reasons a resignation is not accepted.

What are my voting choices on Proposal 2, the ratification of the appointment of Whitley Penn LLP as the Company’s independent registered public accounting firm?

For the vote on the ratification of the appointment of our independent registered public accounting firm, Voting Shareholders may:

Our Board recommends that you vote “FOR” Proposal 2.

What vote is required to ratify the appointment of the Company’s independent registered public accounting firm?

The proposal to ratify the appointment of our independent registered public accounting firm requires the FOR vote of the holders of a majority of the shares entitled to vote on the proposal and represented electronically during the live audio-only webcast or by proxy at the Annual Meeting.

What are my voting choices on Proposal 3, the advisory vote to approve our executive compensation?

For the advisory vote on executive compensation, Voting Shareholders may:

Our Board recommends that you vote “FOR” Proposal 3.

What vote is required for the advisory approval of the Company’s executive compensation?

The Company’s executive compensation will be approved by the Voting Shareholders, on an advisory basis, if the votes cast FOR the proposal are a majority of the shares entitled to vote on the proposal and represented electronically during the live audio-only webcast or by proxy at the Annual Meeting.

How often will the Company hold an advisory vote to approve executive compensation?

At our 2017 Annual Meeting of Shareholders, our shareholders voted, in an advisory vote, on various frequencies for conducting future advisory votes with respect to compensation of our named executive officers, with an annual frequency receiving the most advisory votes that were cast. After considering those voting results and other factors, our Board determined that the Company would hold an annual advisory vote on the compensation of our named executive officers until (a) the next required vote on the frequency of shareholder votes on the compensation of our named executive officers or (b) the Board otherwise determines that a different frequency for such advisory votes is in the best interests of our shareholders.

What are my voting choices on Proposal 4, the approval of the 2021 Plan?

For the vote on the approval of the 2021 Plan, shareholders may:

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Our Board recommends that you vote “FOR” Proposal 4.

What vote is required for the approval of the 2021 Plan?

The proposal to approve the 2021 Plan requires the FOR vote of the holders of a majority of the shares entitled to vote on the proposal and represented in person or by proxy at the Annual Meeting and entitled to vote thereon.

What if a Voting Shareholder does not specify a choice for a matter when returning a proxy?

Voting Shareholders should specify their choice for each proposal described on the enclosed proxy card. Proxy cards that are signed and returned will be voted FOR proposals described in this proxy statement for which no specific instructions are given.

How are withheld votes, abstentions and broker non-votes counted?

Both abstentions and broker non-votes are counted as “present” for purposes of determining the existence of a quorum at the Annual Meeting. Shares voted WITHHELD as to a director nominee on Proposal 1 will have no effect on the election of the nominees, but, for purposes of the Majority WITHHELD Vote and the effectiveness of a nominee’s conditional resignation, will count as votes against the indicated nominee. Shares voted ABSTAIN on Proposals 2, 3 and 4 will have the same effect as votes cast AGAINST that proposal. Broker non-votes will not be included in vote totals and will not affect the outcome of the vote on the proposals.

Why did I receive more than one Proxy Statement?

If you received more than one Proxy Statement, your shares are probably registered in different names or are in more than one account. Please vote each proxy card that you receive.

What if I want to change my vote?

You may revoke your vote on any proposal at any time before the Annual Meeting for any reason. To revoke your proxy before the meeting, write to Zix Corporation, Attention: Corporate Secretary, 2711 North Haskell Avenue, Suite 2300, LB 36, Dallas, Texas 75204-2960. You will need to include a copy of your earlier voted proxy and may be required to provide other information to facilitate the administrative steps actually required to properly revoke your prior proxy and properly record the revocation. You may also attend the virtual Annual Meeting and change your vote by electronically voting your shares. Attendance at the virtual Annual Meeting will not cause your previously granted proxy to be revoked unless you specifically so request or cast your vote electronically at the virtual meeting.

Where will I find the voting results of the Annual Meeting?

We will announce the preliminary voting results at the Annual Meeting and will publish the preliminary or final voting results in a Current Report on Form 8-K that we will file with the SEC within four business days after the Annual Meeting. If the voting results are not final when that Current Report is filed, we will publish the final voting results in a Current Report on Form 8-K that we will file with the SEC within four business days after the final voting results are determined. You may request a copy of either Current Report at investor.zixcorp.com or by contacting Investor Relations at (949)-574-3860.

How can I submit a question for the Annual Meeting?

By accessing www.proxyvote.com, our shareholders will be able to submit questions in writing in advance of our Annual Meeting, vote, view the annual meeting procedures, and obtain copies of proxy materials and our 2020 Annual Report on Form 10-K. Shareholders may also submit questions in writing on the day of or during the Annual Meeting at www.virtualshareholdermeeting.com/ZIXI2021. Shareholders will need their unique control number which appears on the notice regarding the availability of proxy materials, the proxy card (printed in the box and marked by the arrow) and the instructions that accompanied the proxy materials.

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As part of the Annual Meeting, we will hold a live question and answer session, during which we intend to answer all questions submitted in writing before or during the virtual meeting in accordance with the annual meeting procedures, as time permits. Questions and answers will be grouped by topic and substantially similar questions will be grouped and answered once.

What if I need Technical Assistance?

Beginning 20 minutes prior to the start of and during the virtual Annual Meeting, we will have a support team ready to assist shareholders with any technical difficulties they may have accessing or hearing the virtual meeting. If you encounter any difficulties accessing the virtual meeting during the check-in or meeting time, please call the technical support number that will be posted on the Virtual Shareholder Meeting log-in page.

Where can I find additional information? Who can help answer my questions?

You should carefully review the entire Proxy Statement, which contains important information regarding the proposals, before voting. The section titled “WHERE YOU CAN FIND MORE INFORMATION” describes additional sources from which to obtain this Proxy Statement, our public filings under the Securities Exchange Act of 1934 and other information about our Company. Additionally, a copy of this Proxy Statement is available on our Company’s website at investor.zixcorp.com.

If you would like additional copies of this Proxy Statement or other documents that we have filed with the SEC that are incorporated by reference into this Proxy Statement, free of charge, or if you have questions about the proposals or the procedures for voting your shares, please contact: Zix Corporation, Attention: Corporate Secretary, 2711 North Haskell Avenue, Suite 2300, LB 36, Dallas, Texas 75204-2960 or (214) 370-2000.

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ZIX CORPORATION

2711 North Haskell Avenue

Suite 2300, LB 36

Dallas, Texas 75204-2960

PROXY STATEMENT

Annual Meeting of Shareholders

June  5, 20199, 2021

Information Concerning Solicitation and Voting

General

This Proxy Statement is furnished on behalf of the Board of Directors (the “Board”) of Zix Corporation (“we,” “us,” “our” or the “Company”) to solicit proxies to be voted at the Annual Meeting of our Shareholders to be held on Wednesday, June 5, 2019,9, 2021, at 10:00 a.m. Central Time, and at any adjournment or postponement of the Annual Meeting for the purposes set forth herein and in the accompanying Notice of Annual Meeting of Shareholders.

Whether or not you personally attend the virtual audio-only Annual Meeting, it is important that your shares entitled to vote be represented and voted at the Annual Meeting. Most holders of our common stock and our Series A Preferred Stock (collectively, our “Voting Shareholders”) have a choice of voting over the Internet, by using a toll-free telephone number, or by completing a proxy card and mailing it in the postage-paid envelope provided. Check your proxy card or the information forwarded by your bank, broker, or other Voting Shareholder of record to determine which voting options are available to you. Please be aware that if you vote over the Internet, you may incur costs such as telecommunication and Internet access charges for which you will be responsible. The Internet voting and telephone voting facilities for Voting Shareholders of record will be available until 11:59 p.m. Eastern Time on June 4, 2019.8, 2021. This Proxy Statement and the accompanying proxy card were first mailed on or about April 26, 2019.23, 2021.

NO PERSON IS AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY REPRESENTATIONS OTHER THAN THOSE CONTAINED IN THIS PROXY STATEMENT, AND, IF GIVEN OR MADE, THE INFORMATION OR REPRESENTATIONS MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORIZED. THE DELIVERY OF THIS PROXY STATEMENT SHALL, UNDER NO CIRCUMSTANCES, CREATE ANY IMPLICATION THAT THERE HAS BEEN NO CHANGE IN OUR AFFAIRS SINCE THE DATE OF THIS PROXY STATEMENT.

Solicitation of Proxies

The Company is making this solicitation on behalf of our Board. The Company will bear the expense of the preparation, printing and distribution of the enclosed proxy card, Notice of Annual Meeting of Shareholders and this Proxy Statement, and any additional material relating to the Annual Meeting that may be furnished to our shareholders by our Board related to the furnishing of this Proxy Statement. We have engaged Georgeson Inc. to assist in the solicitation of proxy materials from Voting Shareholders at a fee of approximately $7,500$8,500 plus reimbursement of reasonableout-of-pocket expenses. Proxies may also be solicited without additional compensation by our officers or employees by telephone, faxe-mail, or personal interview.e-mail. We will reimburse banks and brokers who hold shares in their name or custody, or in the name of nominees for others, for theirout-of-pocket expenses incurred in forwarding copies of the proxy materials to those persons for whom they hold those shares. To obtain the necessary representation of Voting Shareholders at the Annual Meeting, supplementary solicitations may be made by mail, telephone, fax or e-mail or personal interview by our officers or employees, without additional compensation, or by selected securities dealers. We anticipate that the cost of those supplementary solicitations, if any, will not be material.

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Purpose of Annual Meeting

The purpose of the Annual Meeting is to obtain approval for the proposals described in this Proxy Statement and to consider any other business properly brought before the Annual Meeting or any adjournment or postponement thereof. At the meeting,Annual Meeting, we will ask Voting Shareholders to consider and vote on the following proposals:

Record Date and Shares Outstanding

Only shareholders who owned shares of our common stock and our Series A Preferred Stock at the close of business on April 12, 2019,2021, referred to in this Proxy Statement as the “Record Date,” are entitled to notice of, and to vote at, the Annual Meeting. As of the Record Date, 55,596,18057,058,008 shares of our common stock were outstanding and entitled to vote at the Annual Meeting. Holders of our common stock are entitled to one vote, in person or by proxy, for each share of common stock held in their name on the Record Date.

As of the Record Date, 64,914100,206 shares of our Series A Preferred Stock were outstanding and entitled to vote on anas-converted basis at the Annual Meeting. As of the Record Date, the 64,914100,206 shares of Series A Preferred Stock were convertible into 10,910,12419,733,971 shares of common stock. However, under applicable Nasdaq Listing Rules,

As of the number ofrecord date, there were no shares of common stock into which theour Series AB Preferred Stock can be converted, when aggregated with any other common stock held by such holder, cannot exceed 19.9% of the number of our shares of common stock outstanding as of February 20, 2019, immediately prior to the issuance of the Series A Preferred Stock. Additionally, under applicable Nasdaq Listing Rules, the number of votes that a holder of Series A Preferred Stock will be entitled to cast on any matter to be voted upon, when aggregated with any of our other voting securities held by such holder, cannot exceed 19.9% of the number of our voting securities outstanding as of February 20, 2019, immediately prior to the issuance of the Series A Preferred Stock. For the record holder of Series A Preferred Stock as of the Record Date, the number of shares of common stock into which the Series A Preferred Stock can convert and the number of votes that the holder of Series A Preferred Stock is entitled to cast on any matter to be voted upon is capped at 10,783,050 (the “Nasdaq Cap”).outstanding.

Quorum

A majority of the outstanding shares of our common stock entitled to vote at the Annual Meeting (including the Series A Preferred Stock on anas-converted basis, subject to the Nasdaq Cap)basis) must be represented, in personelectronically during the live audio-only webcast or by proxy, at the Annual Meeting to constitute a quorum to conduct business at the meeting. As of the Record Date, 66,379,23076,791,979 shares of our common stock (including the Series A Preferred Stock on anas-converted basis, subject to the Nasdaq Cap)basis) were outstanding and entitled to vote at the Annual Meeting, so we will require a quorum of at least 33,189,61638,395,991 shares of our common stock (including the Series A Preferred Stock on anas-converted basis, subject to the Nasdaq Cap)basis) represented at the Annual Meeting in order to conduct business at the meeting.

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Dissenters’ Rights

Under Texas law, shareholders are not entitled to dissenters’ rights with respect to any of the proposals that will be considered at the Annual Meeting.

Tabulation of Votes

Votes cast at the Annual Meeting will be tabulated by a representative of Broadridge Financial Solutions, Inc. as the independent inspector of election.

Vote Required to Approve Proposals

Proposal 1

On Proposal 1, shares may either be voted FOR an individual director nominee or voted WITHHELD as to an individual director nominee. If a quorum is represented at the Annual Meeting, the eight nominees who receive the greatest number of FOR votes (also called a “plurality” of FOR votes) will be elected as directors. Brokers cannot cast discretionary votes in the election of directors, so you must instruct your broker how to vote your shares on Proposal 1. Brokernon-votes will not be included in vote totals and will not affect the outcome of the vote on this proposal. A vote WITHHELD as to any director will have no effect on the election of the nominees, but, for purposes of the Majority WITHHELD Vote (as described in the Question and Answer section of this Proxy Statement) and the effectiveness of a nominee’s conditional resignation, will be counted as a vote against the election of that director. In the election of directors, shareholders are not entitled to cumulate their votes or to vote for a greater number of persons than the number of nominees named in this Proxy Statement.

Proposal 2

On Proposal 2, shares may either be voted FOR the ratification of the appointment of Whitley Penn LLP as the Company’s independent auditors for the fiscal year ending December 31, 2019,2021, or voted AGAINST that ratification, or voted to ABSTAIN. If a quorum is represented at the Annual Meeting, the approval of

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Other Matters

An affirmative vote of a majority of the shares represented at the Annual Meeting is generally required for action on any other matters that may properly come before the Annual Meeting. Our bylaws require the affirmative vote of a majority of the shares outstanding (as opposed to a mere majority of shares represented at a meeting) in order to remove a director or amend our bylaws.

Effect of BrokerNon-Votes

If your shares are held in a brokerage account and you do not instruct your broker how to vote on a particular proposal, your brokerage firm could either:

A broker“non-vote” occurs when a broker or nominee holding shares for a beneficial owner does not vote on a particular proposal because the broker or nominee does not have the discretionary voting power with respect to that proposal and has not received instructions from the beneficial owner. Brokers do not have discretionary authority to vote on Proposals 1, 3 or 4, but they do have the discretionary authority to vote on Proposal 2.

Shareholders’ Proposals

If you would like to submit a proposal to be included in the Proxy Statement for our 20202022 Annual Meeting of Shareholders to be held next year, the submission must be in writing and received by us no later than

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Proposals

PROPOSAL 1 — ELECTIONOF DIRECTORIRECTORSs

Our Voting Shareholders will vote on the election of eight members of our Board at the Annual Meeting. Each director will serve until the next Annual Meeting of Shareholders and until the director’s successor is duly elected and qualified, unless earlier removed in accordance with our bylaws.

The nominees for election to our Board are:

For biographical and other information regarding the nominees for director, please see“see“OTHER INFORMATION YOU NEED TO MAKE AN INFORMED DECISION — Directors.” For information on our directors’ compensation, please see “INFORMATION ON THE COMPENSATION OF DIRECTORS.”

Each of the persons nominated for election to our Board has agreed to stand for election. Our Board has no reason to believe that any of the nominees will be unable or unwilling to serve if elected, and to the knowledge of the Board, each of the nominees intends to serve the entire term for which election is sought. Our bylaws provide that the Board may reduce the number of positions on our Board. In addition, our bylaws provide that the Board may fill any vacancy in the Board by the affirmative vote of a majority of the remaining directors.

The eight nominees who receive the greatest number of FOR votes (also called a “plurality” of FOR votes) will be elected as directors. Brokernon-votes will not be included in vote totals and will not affect the outcome of the vote on this proposal. A vote WITHHELD as to any director will have no effect on the election of the nominees, but, for purposes of the Majority WITHHELD Vote (as described in the Question and Answer section of this Proxy Statement) and the effectiveness of a nominee’s conditional resignation, will be counted as a vote against the election of that director.

OUR BOARD RECOMMENDS THAT YOU VOTE

FOR PROPOSAL 1 ANDFOR EACH DIRECTOR NOMINEE NAMED ABOVE.

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PROPOSAL 2 — RATIFICATIONOF APPOINTMENTOF ACCOUNTANTS

The Audit Committee of the Board (the “Audit Committee”) has recommended, and the Board has appointed, Whitley Penn LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2019.2021. Services provided to the Company and its subsidiaries by Whitley Penn LLP in fiscal 20182020 are described under “Independent Registered Public Accountants.”

We are asking our Voting Shareholders to ratify the appointment of Whitley Penn LLP as our independent registered public accounting firm for the 20192021 fiscal year. Although ratification is not required by our bylaws or otherwise, the Board is submitting the appointment of Whitley Penn LLP to our Voting Shareholders for ratification as a matter of good corporate practice.

A representative of Whitley Penn LLP will be present at the Annual Meeting to respond to appropriate questions and to make any statements that the firm may desire.

Votes cast FOR Proposal 2 by a majority of the shares of our common stock (including the Series A Preferred Stock on anas-converted basis, subject to the Nasdaq Cap)basis) represented at the Annual Meeting is required to approve Proposal 2. Shares voted to ABSTAIN as to Proposal 2 will be counted as represented at the meeting and will have the same effect as a vote against Proposal 2.

If our Voting Shareholders do not approve Proposal 2, the appointment of Whitley Penn LLP will be reconsidered by our Audit Committee and our Board. Even if Proposal 2 is approved, the Audit Committee in its discretion may select a different independent registered public accounting firm if it determines that a change would be in the best interests of the Company and our shareholders and otherwise complies with all regulations of the SEC regarding a change in public accounting firms.

OUR BOARD RECOMMENDS

THAT YOU VOTEFOR PROPOSAL 2.

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PROPOSAL 3 — APPROVE,ONAN ADVISORYBASIS,THE COMPENSATIONOFOUR NAMED EXECUTIVE OFFICERS

The Dodd-Frank Wall Street Reform and Consumer Protection Act enables the Company’s Voting Shareholders to vote to approve, on an advisory (nonbinding) basis, the compensation of the Company’s named executive officers. The Company seeks your advisory vote and asks that you support the compensation of the named executive officers as disclosed in this proxy statement. Our Board intends to conduct an annual advisory vote on the compensation of the Company’s named executive officers.

As described in detail under “COMPENSATION DISCUSSION AND ANALYSIS,” our compensation program is designed to attract, retain and motivate our executives and drive overall Company performance. We believe that our compensation program, with its balance of short-term incentives and long-term incentives (including both time-based and performance-based equity awards that vest over multiple years), rewards sustained performance that is aligned with shareholder interests.

This proposal, commonly known as a“say-on-pay” proposal, gives the Company’s shareholders the opportunity to express their views on the compensation of our named executive officers. This vote is not intended to address any specific item of compensation, but rather the overall compensation of the Company’s named executive officers described in this proxy statement.

Accordingly, the Board invites you to review carefully the section titled “COMPENSATION DISCUSSION AND ANALYSIS” beginning on page 3035 and the tabular and other disclosures on compensation under “2018“2020 Executive Compensation” beginning on page 4349 and to cast a vote to approve the compensation of the Company’s named executive officers through the following resolution:

“Resolved, that shareholders approve the compensation of the Company’s named executive officers, as discussed and disclosed in the Compensation Discussion and Analysis, the executive compensation tables, and any narrative executive compensation disclosure contained in this proxy statement.”

Thesay-on-pay vote is advisory, and therefore not binding on the Company, the Compensation Committee of the Board (the “Compensation Committee”) or the Board. The Board and Compensation Committee value the opinions of the Company’s shareholders and to the extent there is any significant vote against the named executive officers’ compensation as disclosed in this proxy statement, the Board will consider the shareholders’ concerns and the Compensation Committee will evaluate whether any actions are necessary to address those concerns.

At our 2017 Annual Meeting of Shareholders, our shareholders voted, in an advisory vote, on various frequencies for conducting future advisory votes with respect to the compensation of our named executive officers, with an annual frequency receiving the most advisory votes that were cast. After considering those voting results and other factors, our Board determined that the Company would hold an annual advisory vote on the compensation of our named executive officers until (a) the next required vote on the frequency of shareholder votes on the compensation of our named executive officers or (b) the Board otherwise determines that a different frequency for such advisory votes is in the best interests of our shareholders.

OUR BOARD RECOMMENDS

THAT YOU VOTEFOR PROPOSAL 3.

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PROPOSAL 4 — APPROVALOF NASDAQ2021 PROPOSALLAN

BackgroundThe Board has unanimously approved the Zix Corporation 2021 Omnibus Incentive Plan (the “2021 Plan”) to replace the Zix Corporation Amended and Overview

On January 14, 2019, we entered into an Investment AgreementRestated 2018 Incentive Plan (the “Investment Agreement”) for the sale of 64,914 shares of Series A Convertible Preferred Stock (the “Series A Preferred Stock”) and 35,086 shares of Series B Convertible Preferred Stock (the “Series B Preferred Stock” and, together with the Series A Preferred Stock, the “Preferred Stock”) with an investment fund managed by True Wind Capital Management, L.P. (“True Wind”) for an aggregate purchase price of $100 million (the “Private Placement”). The closing of the Private Placement occurred on February 20, 2019. Proceeds from the Private Placement were used to fund our acquisition of 100% of the equity interest of AR Topco, LLC and its subsidiaries, including AppRiver, LLC, on February 20, 2019 (the “AppRiver Acquisition”).

On January 17, 2019 and on February 22, 2019, we filed with the SEC Current Report on Form8-K (“Form8-K’s”) that described the terms of the Private Placement. We filed as Exhibit 10.1 to the Form8-K, dated January 14, 2019, and filed with the SEC on January 17, 2019, the Investment Agreement and as Exhibits 3.1, 3.2 and 10.1, to the Form8-K, dated February 20, 2019 and filed with the SEC on February 22, 2019, the Certificate of Designations of Series A Convertible Preferred Stock, the Certificate of Designations of Series B Convertible Preferred Stock and a related Registration Rights Agreement, respectively. We refer you to the Form8-K’s and the exhibits thereto for a further description of the Private Placement, the Series A Preferred Stock and the Series B Preferred Stock.

Why We Need Shareholder Approval

As a result of being listed for trading on the Nasdaq Stock Market (“Nasdaq”“Prior Incentive Plan”), issuances of our common stock are subject to the Nasdaq Stock Market Rules, including Nasdaq Listing Rule 5635.

Nasdaq Listing Rule 5635(a) requires shareholder approval for issuances of securities in connection withat the acquisition ofAnnual Meeting, and recommends that the stock or assets of another company if afterCompany’s shareholders approve and adopt the transaction a person or entity will hold 20% or more of the outstanding shares of common stock or voting power of the listed company.2021 Plan. We are seeking shareholder approval of the Nasdaq Proposal in orderintend to satisfy the requirements of Nasdaq Listing Rule 5635(a) with respect to the issuancereserve 5,650,000 of shares of our common stock for issuance pursuant to True Windawards under the 2021 Plan.

The Company considers the 2021 Plan an essential element of total compensation and believes the 2021 Plan promotes its interests and the interests of its shareholders by: (i) attracting and retaining the services of employees, officers, directors and consultants upon whose judgment, interest and special effort the successful conduct of the Company��s operation in connectionlargely dependent; and (ii) encouraging the active interest of those persons in the development and financial success of the Company by granting awards designed to provide participants in the 2021 Plan with proprietary interest in the Private Placement that would exceed 20%growth and performance of the Company.

A total of 6,000,000 shares of our outstanding shares of common stock were authorized for grant under the Prior Incentive Plan. As of March 31, 2021, 585,611 shares remained available for grant under the Prior Incentive Plan, as described further in the table below. See also “Compensation Discussion and voting power.Analysis— Equity Compensation Plan Information” for additional information concerning our equity compensation plan.

Further, Nasdaq Listing Rule 5635(b) requires shareholder approval for issuances of securitiesIf our shareholders approve the 2021 Plan, it will replace the Prior Incentive Plan, such that, (i) no additional grants will resultbe made pursuant to the Prior Incentive Plan, and (ii) any previously granted awards that are outstanding under the Prior Incentive Plan will remain outstanding in a “change of control” ofaccordance with their terms. If our shareholders should fail to approve the issuer. This rule does2021 Plan, it will not specifically define when a changebecome effective and the Prior Incentive Plan will continue in control of an issuerforce and effect. However, if the 2021 Plan is not approved by our shareholders, we may not be able to continue our equity-based long-term incentive program, and we may be deemedrequired to occur; however, Nasdaq suggestsincrease the cash component of our executive compensation program in its guidance that a change of control would occur, subjectorder to certain limited exceptions, if after a transaction a person or entity will hold 20% or more of the outstanding shares of common stock or voting power of an issuerremain competitive and such ownership or voting power of an issuer would represent the largest ownership position in the issuer. We are seeking shareholderadequately compensate our employees.

Shareholder approval of the Nasdaq Proposal in order 2021 Plan would also constitute approval for purposes of satisfying the shareholder approval requirements under Section 422 of the Code so that the Compensation Committee or such other committee of our Board that may be designated to administer the 2021 Plan (the “Committee”) may grant incentive stock options, or ISOs.

Best Practices

Independent Oversight. The Committee, composed solely of independent directors, will approve all grants made under the 2021 Plan other than grants made to non-employee directors which will be approved by our Board. Additionally, the Committee may delegate to other committees of the Board, to the Chief Executive Officer and to our other senior officers its duties under the 2021 Plan pursuant to such conditions or limitations as the Committee may establish; provided, however, that such delegation will not extend to the authority to make awards to participants who are subject to Section 16 of the Exchange Act.

No Repricing of Options or SARs. The 2021 Plan prohibits repricing, replacement and regranting of stock options or stock appreciation rights (“SARs”) at lower prices unless approved by our shareholders.

No Discounted Options or SARs. Stock options and SARs may not be granted with an exercise price below the closing price of our common stock on the date of grant.

No Dividends on Options or SARs. Dividends and dividend equivalents may not be paid or accrued on stock options or SARs.

Limited Terms for Options and SARs. Stock options and SARs granted under the 2021 Plan are limited to 10-year terms.

No Liberal Share Counting with Respect to Options or SARs. Shares of our common stock that are (i) not issued or delivered as a result of the net settlement of a stock-settled SAR or option, (ii) withheld or delivered

to satisfy the requirementsapplicable withholding taxes related to an award, (iii) used to satisfy the exercise price related to an option or SAR, or (iv) repurchased on the open market with the proceeds of Nasdaq Listing Rule 5635(b) with respectan option’s exercise price will not become available again for awards under the 2021 Plan.

No Dividends or Dividend Equivalents on Unvested Awards. The right to receive payment of dividends or dividend equivalents will be forfeited to the extent that an underlying award of restricted stock or restricted stock units do not vest, are forfeited or are otherwise cancelled.

Annual Limitation on Director Awards and Compensation. The aggregate grant value of awards and cash compensation paid to any individual non-employee director may not exceed $1,000,000 in any calendar year. The extent to which such awards may be granted may be further limited pursuant to the terms, conditions and parameters of a plan, program or policy for the compensation of nonemployee directors as in effect from time to time.

Clawback or Recoupment. Awards granted under the 2021 Plan will be subject to any clawback policy implemented by the Company.

No Transferability. Awards generally may not be transferred, except by will or the laws of descent and distribution or pursuant to a qualified domestic relations order, unless otherwise provided in the applicable award agreement.

No “Evergreen” Provision. Shares of our common stock authorized for issuance under the 2021 Plan will not be replenished automatically. Any additional shares to be issued over and above the amount for which we are seeking authorization must be approved by our shareholders.

No Automatic Grants. There are no automatic grants to new participants or “reload” grants when outstanding awards are exercised, expire or are forfeited.

No Tax Gross-Ups. Participants do not receive tax gross-ups under the 2021 Plan.

Information on Equity Compensation Plans as of March 31, 2021

The information included in this Proxy Statement and our 2020 Annual Report is updated by the following information regarding all existing equity compensation plans as of March 31, 2021:

The Compensation Committee took the above information on existing equity compensation plan awards into account in setting the number of authorized shares in the proposed 2021 Plan.

Summary of the 2021 Plan

A description of the 2021 Plan is set forth below. Because the description of the 2021 Plan in this proxy statement is a summary, it may not contain all the information that may be important to you. The summary is qualified in its entirety by reference to the 2021 Plan. You should carefully read the 2021 Plan, a copy of which is attached hereto as Appendix A to this proxy statement.

Eligibility

Persons eligible for “Awards” (as defined in the 2021 Plan) are (i) all employees of the Company and its subsidiaries, (ii) non-employee directors and (iii) certain independent contractors. As of March 31, 2021, approximately 40 employees and non-employee directors would be eligible for grants of Awards under the 2021 Plan.

Shares Available for Awards

The aggregate number of shares of our common stock reserved and available for issuance pursuant to True Wind in connectionAwards granted under the 2021 Plan will be 5,650,000, all of which may be issued as incentive stock options under Section 422 of the Code. The closing price per share of our common stock on March 29, 2021 was $7.27.

Each share of our common stock subject to an Award granted under the 2021 Plan is counted against the above share reserve as one share. If an Award expires or is terminated, cancelled or forfeited, the shares associated with the Private Placementexpired, terminated, cancelled or forfeited Awards immediately become available for additional Awards under the 2021 Plan, it being understood that could be considered a “change of control” under that Nasdaq Listing Rule. Shareholders should note that a “change of control,” as described under Nasdaq Listing Rule 5635(b), applies onlyno increase or decrease in the above share reserve occurs with respect to the application of such rule and does not constitute a “change of control” for purposes of Texas law, our organizational documents, U.S. income tax laws or any other purpose.

Finally, pursuant to the Investment Agreement, we agreed to include the Nasdaq Proposalan Award that can only be settled in our proxy statement prepared and filed with the SEC in connection with our 2019 Annual Meeting.

Effect on Current Shareholders if the Nasdaq Proposal is Approved

If the Nasdaq Proposal is approved by our shareholders at the 2019 Annual Meeting on June 5, 2019, on the business day immediately following such approval, the 35,086 outstanding shares of our Series B

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The Committee also may delegate to other committees of the Board, to the Chief Executive Officer and to our other senior officers its duties under the 2021 Plan to the extent allowed by applicable law.

The Committee will determine the employees and independent contractors to receive Awards and the terms, conditions and limitations applicable to each such Award, which terms, conditions and limitations may, but need not, include continuous service with the Company, achievement of specific business objectives, attainment of specified growth rates, increases in specified indices or other comparable measures of performance.

Amendment; Termination

The Board may amend, modify, suspend or terminate the 2021 Plan for the purpose of addressing any changes in legal requirements or for any other lawful purpose, except that no amendment that would adversely affect the rights of any participant under any Award previously granted to such participant may be made without the consent of such participant unless the amendment is reasonably necessary for such Award to comply with applicable law. In addition, no amendment will be effective prior to its approval by the shareholders of the Company to the extent such approval is required pursuant to Rule 16b-3 in order to preserve the applicability of any exemption provided by such rule to any Award then outstanding (unless the holder of such Award consents) or to the extent shareholder approval is otherwise required by applicable law.

Adjustments

Depending on the transaction described below, the Board either will or may make certain adjustments, including changes to the shares of our common stock subject to outstanding Awards and shares available for grant under the 2021 Plan, in the event of any subdivision, split or consolidation of outstanding shares, any declaration of a stock dividend payable in shares, any recapitalization or capital reorganization of the Company, any consolidation or merger of the Company with another corporation or entity, any adoption by the Company of any plan of exchange affecting the common stock or any distribution to holders of common stock of securities or property (other than normal cash dividends).

Vesting

In general, a minimum vesting or restriction period of one year will apply with respect any Award (or any portion thereof) granted under the 2021 Plan; provided an Award granted to a non-employee Director may vest on the earlier of the one-year anniversary of the date of grant or the next annual meeting of the Company’s shareholders (as long as the vesting period is not less than fifty (50) weeks after the date of grant). However, the minimum vesting or restriction period may end in connection with a participant’s death or termination of employment due to disability or in connection with a Change in Control (as described and defined below) or in connection with a participant’s Employment Termination Benefits Agreement (as described under “Separation Payments and Change in Control Payments” below) or similar agreement. In addition, the minimum vesting or restriction period will not apply to up to 5% of the shares of our common stock (i.e., 300,000 shares) that are reserved for issuance under the 2021 Plan, so long as the award certificate or other contemporaneous writing as of the date of grant designates such dilutionshares as not being subject to such minimum vesting or restriction period.

Change in Control

A “Change in Control” generally occurs upon the occurrence of any of the following: (i) during any consecutive 12-month period, individuals who at the beginning of such period were members of the Board (“Incumbent Directors”) cease for any reason to constitute at least a majority thereof, unless the election of each new director was approved by a vote of at least a majority of Incumbent Directors (for purposes hereof, if an individual’s election as a director was a result of an actual or threatened election contest or proxy contest, they are not deemed an Incumbent Director); (ii) any person or group (that is unaffiliated with the Company) becomes the beneficial owner of either 30% or more of the then-outstanding shares of our common stock or securities of the Company representing 25% or more of the combined voting power; (iii) the consummation of a reorganization, merger, sale of substantially all of the Company’s assets or similar transaction, unless (x) substantially all beneficial owners of the Company prior to the transaction continue to hold more than 50% of the surviving entity’s common stock and total voting power, (y) a majority of the directors of the surviving entity are Incumbent Directors, and (z) no person or

group (that is unaffiliated with the Company) is the beneficial owner of either 30% or more of the surviving entity’s common stock or securities of the surviving entity representing 25% or more of the total voting power.

Unless otherwise provided in the award certificate or other agreement with a participant, the treatment of a participant’s Awards in connection with a Change in Control will increase over timedepend on (i) whether Awards are assumed by the surviving entity or are otherwise equitably converted or substituted in connection with the future accretionChange in Control in a manner approved by the Committee or the Board (a “Qualifying Conversion/Assumption”), and (ii) whether a participant’s employment is terminated without cause or the participant resigns for good reason within the one-year period after the effective date of the Series A Preferred Stock. The Series A Preferred Stock accretes atChange in Control (a “Qualifying Termination”). In the event a fixed rate of 8.0% per annum, compounded quarterly.

IfQualifying Conversion/Substitution does not occur in connection with a Change in Control, then: (x) options and SARs will become fully exercisable immediately prior to the Nasdaq Proposal is approved by our shareholders, thereChange in Control, (y) time-based vesting requirements on outstanding Awards will be no capdeemed to be satisfied in full immediately prior to the Change in Control, and (z) all performance-based vesting requirements on the voting poweroutstanding Awards will be deemed to be satisfied on a pro-rata basis at 100% of the Series A Preferred Stock. Assuming“target” level immediately prior to the Nasdaq Proposal is approvedChange in Control. In the event a Qualifying Conversion/Substitution occurs in connection with a Change in Control, but a participant incurs a Qualifying Termination, then: (A) such participant’s options and SARs will become fully exercisable, (B) time-based vesting requirements on such participant’s outstanding Awards will be deemed to be satisfied in full, and (C) all performance-based vesting requirements on such participant’s outstanding Awards will be deemed to be satisfied on a pro-rata basis at 100% of the 2019 Annual Meeting on June 5, 2019,“target” level.

Clawback

Awards under the one holder2021 Plan will be subject to the provisions of our Series A Preferred Stock will have aggregate voting powerany clawback policy either required by applicable law or otherwise implemented by the Company, which clawback policy may provide for forfeiture, repurchase and/or recoupment of Awards and amounts paid or payable pursuant to or with respect to approximately 23.8%Awards.

Awards

At the discretion of the Committee or the Board, as applicable, employees, independent contractors or non-employee directors may be granted Awards under the 2021 Plan in the form of stock options, SARs, restricted stock, restricted stock units, cash awards, performance awards, or any other right or interest relating to shares of our common stock or cash. Such Awards may be granted singly, in combination, or in tandem.

Options

Awards may be in the form of options, which are rights to purchase a specified number of shares of our common stock at a specified price not less than that of the fair market value of a share of common stock on the date of grant. An option may be either an incentive stock option (“ISO”) that is intended to comply, or a nonqualified stock option (“NSO”) that is not intended to comply, with the requirements of Section 422 of the Code; provided that independent contractors and non-employee directors cannot be awarded ISOs. The Committee will determine the participants to receive options and the terms, conditions and limitations applicable to each such option. The term of each option may not be longer than a period of 10 years from the date of grant. Except as otherwise provided in an award certificate, any option (i) that remains outstanding capital stock (using outstanding sharesas of the last day of its term, (ii) has an exercise price per share that is less than the fair market value of a share of common stock as of March 7, 2019) followingsuch day and (iii) whose exercise is prohibited as of such day pursuant to the automatic conversionoperation of the Series B Preferred Stock into Series A Preferred Stock. In addition,Company’s insider trading policy, will be automatically exercised (without any action on the aggregate voting powerpart of the Series A Preferred Stock will increase further in connection with future accretionparticipant holding such option) by (x) foregoing the delivery of shares otherwise deliverable upon the exercise of the Series A Preferred option in an amount sufficient to pay the exercise price of the option and (y) satisfying tax withholding obligations by withholding from the shares otherwise deliverable upon the exercise of the option using the minimum tax rate applicable to the participant.

Stock for as long asAppreciation Rights

Awards may also be in the Series A Preferred Stock remains outstanding. Holdersform of Series A Preferred StockSARs, which are entitledrights to vote together withreceive a payment, in cash or shares of our common stock, equal to the holdersfair market value or other specified value of a number of shares on the rights exercise date over a specified strike price not less than the fair market value of a share of common stock on anas-converted basis, on all matters submitted tothe date of grant. The term of each SAR may not be longer than a voteperiod of ten (10) years from the date of grant. Except as otherwise

provided in an award certificate, any SAR (i) that remains outstanding as of the holderslast day of its term, (ii) has a strike price per share that is less than the fair market value of a share of common stock. This means thatstock as of such day and (iii) whose exercise is prohibited as of such day pursuant to the operation of the Company’s insider trading policy, will be automatically exercised (without any action on the part of the participant holding such SAR) and any tax withholding obligations will be satisfied by withholding from the cash or shares otherwise deliverable upon the exercise of the SAR using the minimum tax rate applicable to the participant.

Stock Awards

Awards may also be in the form of grants of common stock or units denominated in common stock, including restricted stock and restricted stock units (“Stock Awards”). The terms, conditions and limitations applicable to any Stock Award will be determined by the Committee. At the discretion of the Committee, the terms of a Stock Award may include rights to receive dividends or dividend equivalents, which will only be paid if the underlying shares subject to the Award vest pursuant to the terms of the Stock Award.

Cash Awards

Awards may also be in the form of grants denominated in cash. The terms, conditions and limitations applicable to any cash awards granted pursuant to the 2021 Plan will be determined by the Committee.

Performance Awards

At the discretion of the Committee, any of the above-described Awards may be made in the form of a performance award. A performance award will be paid, vested or otherwise deliverable solely on account of the attainment of one holderor more performance goals, either individually or in any combination, established by the Committee and specified in the award certificate.

A performance goal need not be based upon an increase or positive result under a particular business criterion and could include, for example, maintaining the status quo or limiting economic losses (measured, in each case, by reference to specific business criteria). The amount of cash or shares of our Series A Preferred Stock will have significant influence overcommon stock payable or vested pursuant to performance awards may be adjusted upward or downward, either on a formula or discretionary basis or any combination, as the Committee determines.

Director Award Limits

No non-employee director may be granted during any calendar year Awards (in his or her capacity as a director) having a fair value determined on the date of grant when added to all matterscash compensation paid to the non-employee director during the same calendar year in excess of $1,000,000. The extent to which such Awards may be granted may be further limited pursuant to the terms, conditions and parameters of a plan, program or policy for the compensation of non-employee directors as in effect from time to time.

U.S. Federal Income Tax Consequences

The following is a summary of the general rules of current U.S. Federal income tax law relating to the tax treatment of Awards that require approval by our shareholders, includingmay be issued under the approval2021 Plan. The discussion is general in nature and does not take into account a number of significant corporate transactions.

Effect on Current Shareholders ifconsiderations which may apply in light of the Nasdaq Proposal is Not Approved

If the Nasdaq Proposalparticular circumstances of a participant. This summary is not approvedcomplete and does not attempt to describe any tax consequences arising in the context of the participant’s death or the income tax laws of any local, state or foreign country in which the participant’s income or gain may be taxable.

Stock Awards

Restricted Stock. A participant generally recognizes no taxable income at the time of an Award of restricted stock. A participant may, however, make an election under Section 83(b) of the Code to have the grant taxed as compensation income at the date of receipt, with the result that any future appreciation or depreciation in the value of the shares of stock granted may be taxed as capital gain or loss on a subsequent sale of the shares. If the

participant does not make a Section 83(b) election, the grant will be taxed as compensation income at the full fair market value on the date the restrictions imposed on the shares expire. Unless a participant makes a Section 83(b) election, any dividends paid to the participant on the shares of restricted stock will generally be compensation income to the participant and deductible by our shareholders,us as compensation expense. In general, subject to the Series B Preferred Stocklimitations discussed below, we will receive a deduction for U.S. Federal income tax purposes for any compensation income taxed to the participant. To the extent a participant realizes capital gains, as described above, we will not be converted into Seriesentitled to any deduction for federal income tax purposes.

Restricted Stock Units. A Preferred Stock andparticipant who is granted restricted stock units will remain outstanding pursuant to its current terms, including receipt of dividends accruing daily on a cumulative basis payable quarterly in arrears in cash at a dividend rate of 10.0%, which rate will automatically increase by 1.0% every six months that the Series B Preferred Stock remains outstanding (subject to a cap of 12.0%). We will either be required to pay these dividends in cash or the liquidation preference of each outstanding share of Series B Preferred Stock will automatically increase at the dividend rate, increasing the amount we will pay in connection with any future redemptionrecognize no income upon grant of the Series B Preferred Stock.

Ifrestricted stock units. At the Nasdaq Proposal is not approved by our shareholders,time the Series A Preferred Stock will remain outstanding pursuant to its current terms, including the Nasdaq Cap. The Nasdaq Cap will limit our ability to useunderlying shares of common stock as payment for dividends and for redemption(or cash in lieu thereof) are delivered to a participant, the participant will recognize compensation income equal to the full fair market value of the Series A Preferredshares received. Subject to the limitations discussed below, we will generally be entitled to a deduction for U.S. Federal income tax purposes that corresponds to the compensation income recognized by the participant.

Options; Stock Appreciation Rights

Options granted under the 2021 Plan may constitute ISOs within the meaning of Section 422 of the Code, while other options granted under the 2021 Plan may constitute NSOs. Grants of options to non-employee directors and independent contractors are NSOs. The Code provides for tax treatment of options qualifying as ISOs that may be more favorable to participants than the tax treatment accorded NSOs. Generally, upon the grant or exercise of an ISO, the optionee will recognize no taxable income for U.S. Federal income tax purposes, although the difference between the exercise price of the ISO and the fair market value of the stock at the date of exercise is an addition to income in determining alternative minimum taxable income and such amount may be sufficient in amount to subject the optionee to the alternative minimum tax. On the sale of shares acquired by exercise of an ISO (assuming that the sale does not occur within two years of the grant date or within one year of the exercise date), any gain will be taxed to the optionee as long-term capital gain. Except with respect to death or disability, an optionee has three months after termination of employment in which to exercise an ISO and retain favorable tax treatment at exercise. No deduction is available to the Company upon the grant or exercise of an ISO (although a deduction may be available if the participant disposes of the shares so purchased before the applicable holding periods expire).

In contrast, upon the exercise of an NSO, the optionee recognizes ordinary taxable income on the exercise date in an amount equal to the excess of the fair market value of the shares purchased over the exercise price. Upon the sale of such shares by the optionee, any difference between the fair market value at the date of sale and the fair market value at the date of exercise will be treated generally as capital gain or loss. Subject to the limitations discussed below, upon exercise of an NSO, the Company is entitled to a tax deduction in turn, require usan amount equal to satisfythe ordinary taxable income recognized by the participant.

Participants do not recognize taxable income upon the grant of a SAR. Upon the exercise of a SAR, the participant will recognize ordinary income in an amount equal to the cash or fair market value of the shares received at the date of exercise of the SAR. The participant’s tax basis in any shares received on the exercise of a SAR will generally equal the fair market value of such shares on the date of exercise. Subject to the limitations discussed below, the Company will be entitled to a deduction for U.S. Federal income tax purposes that corresponds as to timing and amount with the taxable income recognized by the participant under the foregoing rules.

Deductibility; Excise Taxes

Code Section 162(m). In general, a U.S. Federal income tax deduction is allowed to the Company in an amount equal to the ordinary taxable income recognized by a participant with respect to Awards granted under the 2021 Plan, provided that such amount constitutes an ordinary and necessary business expense of the Company, that such amount is reasonable and that the Company satisfies any withholding obligations with cash.respect to the participant’s ordinary taxable income. Following the enactment of the Tax Cuts and Jobs Act, beginning with the 2018 calendar year, the $1 million annual deduction limitation under Section 162(m) applies to compensation paid to any individual who serves as the Chief Executive Officer, Chief Financial Officer or qualifies as one of the other three most highly compensated executive officers in 2017 or any later calendar year. See also “Compensation Discussion and Analysis— Impact of Accounting and Tax Treatments of Compensation” for a more robust discussion of Section 162(m) of the Internal Revenue Code.

Change in Control. The acceleration of the Private Placementexercisability or the AppRiver Acquisition,vesting of an Award upon the entry intooccurrence of a change in control may result in an “excess parachute payment” within the meaning of Section 280G of the Code. A “parachute payment” occurs when an employee receives payments contingent upon a change in control that exceed an amount equal to three times his or her “base amount.” The term “base amount” generally means the average annual compensation paid to such employee during the five calendar years preceding calendar year in which the change in control occurs. An “excess parachute payment” is the excess of all parachute payments made to the employee on account of a change in control over the employee’s base amount. If any amount received by an employee is characterized as an excess parachute payment, the employee is subject to a 20% excise tax on the amount of the excess, and the Company is denied a tax deduction with respect to such excess.

Code Section 409A. Section 409A of the Code generally provides that any deferred compensation arrangement must satisfy specific requirements, both in operation and in form, regarding (i) the timing of payment, (ii) the advance election of deferrals, and (iii) restrictions on the acceleration of payment. Failure to comply with Section 409A of the Code may result in the early taxation (plus interest) to the participant of deferred compensation and the imposition of a 20% penalty on the participant on such deferred amounts included in the participant’s taxable income. The Company intends to structure Awards under the 2021 Plan in a manner that is designed to be exempt from or comply with Section  409A of the Code.