This is a list of mail server software: mail transfer agents, mail delivery agents, and other computer software which provide e-mail.
All such figures are necessarily estimates because data about mail server share is difficult to obtain; there are few reliable primary sources—and no agreed methodologies for its collection.
Surveys probing Internet-exposed systems typically attempt to identify systems via their banner, or other identifying features. [1] As of December 2023 [update] , Postfix and exim appeared to be the overwhelming leaders in mail server types, with greater than 92% share between them, having come to prominence before 2010 in each case. [1] [a] While such methods are effective at identifying mail server share for receiving systems, most large-scale sending environments are not listening for traffic on the public internet and will not be counted using such methodologies.
The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typically use SMTP only for sending messages to a mail server for relaying, and typically submit outgoing email to the mail server on port 587 or 465 per RFC 8314. For retrieving messages, IMAP is standard, but proprietary servers also often implement proprietary protocols, e.g., Exchange ActiveSync.
A mail exchanger record specifies the mail server responsible for accepting email messages on behalf of a domain name. It is a resource record in the Domain Name System (DNS). It is possible to configure several MX records, typically pointing to an array of mail servers for load balancing and redundancy.
Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again after a delay, and if sufficient time has elapsed, the email will be accepted.
SquirrelMail is a project that aims to provide both a web-based email client and a proxy server for the IMAP protocol.
Mercury Mail Transport System is a standards-compliant mail server developed by David Harris, who also develops the Pegasus Mail client.
Zimbra Collaboration, formerly known as the Zimbra Collaboration Suite (ZCS) before 2019, is a collaborative software suite that includes an email server and a web client.
The comparison of mail servers covers mail transfer agents (MTAs), mail delivery agents, and other computer software that provide e-mail services.
Push-IMAP, which is otherwise known as P-IMAP or Push extensions for Internet Message Access Protocol, is an email protocol designed as a faster way to synchronise a mobile device like a PDA or smartphone to an email server.
Bynari is a defunct company based in Dallas, developing server and email software, mainly known for its Insight Family, similar to Microsoft Exchange Server with Outlook.
Sun Java System Communications Suite is a collection of "Industrial-Strength" software services from Sun Microsystems. The supported platforms are: Red Hat Enterprise Linux, Solaris and Windows Server. Since Oracle acquired Sun in 2010, collection is now called Oracle Communications Unified Communications Suite.
hMailServer was a free email server for Windows created by Martin Knafve. It ran as a Windows service and includes administration tools for management and backup. It had support for IMAP, POP3, and SMTP email protocols. It could use external database engines such as MySQL, MS SQL or PostgreSQL, or an internal MS SQL Compact Edition engine to store configuration and index data. The actual email messages were stored on disk in a raw MIME format. As of January 15th, 2022, active support and development were officially halted, although version 5.6 will continue to receive updates for critical bugs.
Axigen is a Linux, Windows, and Docker mail server with groupware and collaboration functionalities. It supports SMTP, IMAP, POP3, and webmail services, and includes features such as an integrated mailing list server, Antivirus and Antispam integration options, and various mobile capabilities including mobile-friendly webmail and Exchange ActiveSync support. Axigen can be hosted in data centers, on bare-metal or Private or Public Clouds of choice.
Backscatter is incorrectly automated bounce messages sent by mail servers, typically as a side effect of incoming spam.
Oracle Beehive is collaboration platform software developed by Oracle Corporation that combines email, team collaboration, instant messaging, and conferencing in a single solution. It can be deployed on-premises as licensed software or subscribed to as software-as-a-service (SaaS).
Ipswitch IMail Server is an email server application with groupware functionality that runs on Microsoft Windows OS. It was developed in 1994 by Ipswitch, Inc., a software company based in Lexington, Massachusetts.
GroupWise is a messaging and collaboration platform from OpenText that supports email, calendaring, personal information management, instant messaging, and document management. The GroupWise platform consists of desktop client software, which is available for Windows,, and the server software, which is supported on Windows Server and Linux.
IceWarp Mail Server is a business Email and Collaboration server developed by IceWarp Ltd. It features email with custom domain, shared calendars, documents editing, messaging and advanced tool for team collaboration and can be run in Cloud or on a local server using either Windows or Linux, or together with another solution in Hybrid deployment. In 2006 was known as Merak Mail Server.
MDaemon Email Server is an email server application with groupware functions for Microsoft Windows, first released by Alt-N Technologies in 1996.
The JSON Meta Application Protocol (JMAP) is a set of related open Internet Standard protocols for handling email. JMAP is implemented using JSON APIs over HTTP and has been developed as an alternative to IMAP/SMTP and proprietary email APIs such as Google's Gmail and Microsoft's MAPI . Additional protocols and data models being built on top of the core of JMAP for handling contacts and calendar synchronization are meant to be potential replacements for CardDAV and CalDAV, and other support is currently in the works.