Exim, which was developed by the University of Cambridge, is a free mail transfer agent. It is flexible, but still easy to configure, and provides security via access control lists for the purpose of spam protection. The review of email contents for viruses has also been possible since version 4. Despite the monolithic design, only a small number of critical security problems have been identified over the years.
Exim is used in Debian as standard.
Exim is free software, and its source code is freely available on the project page .
Postfix is an implementation of a mail transfer agent (MTA) as free software. An MTA is responsible for the forwarding and local delivery of emails. Security was a specific focus during the development of the software.
You can find more information on the project page.
Sendmail is an implementation of a mail transfer agent (MTA). An MTA is responsible for the forwarding and local delivery of emails. Sendmail is considered one of the most flexible mail transfer agents.
You can find more information on the project page.
The courier POP3/IMAP server is an extremely stable and established server that reliably and quickly makes emails available in the Maildir.
Dovecot is a free IMAP and POP server that was developed with a special focus on security. It is a streamlined, fast, and easy-to-install mail server. Dovecot supports mbox and Maildir, and also provides an as yet still experimental, native and high-performance format called dbox for storing emails. The software contains a mail delivery agent for local delivery, which can also use the Sieve programming language for filtering. Dovecot offers a range of authentication methods. The server can operate on GNU/Linux as well as other unixoid operating systems.
Dovecot is free software, the source code is available on the project page .
Amavis is an Open Source content filter for mail servers. As a stand-alone filter, Amavis provides protection against spam, malware, and viruses, and also takes over message transfer and interfacing with external filters.
Amavis’ main area of application is email management, especially in the application of filter lists as well as in blocking, redirecting, and archiving emails based on filters for mail size, content, origin, etc.
A common installation of Amavis consists of Postfix as the MTA, SpamAssassin to detect and mark spam mails, ClamAV as virus protection, and Amavis as the stand-alone mail filter.