Exim (originally an acronym for EXperimental Internet mailer ) is a mail transfer agent and mail servers.

Exim is largely call-compatible with the very traditional MTA Sendmail. Its particular strength lies in a very flexible, yet simple configuration.

The program was developed in 1995 at the University of Cambridge by Philip Hazel and is free software. Exim has emerged from Smail. The story of Smail dates way back in the 1980s.

Exim can extract data from a variety of data sources / databases and continue to respond flexibly and save. Furthermore, Exim has built Regular Expressions ( PCRE ) and a simple but very powerful scripting language. Exim also allows to incorporate a Perl interpreter, which own Perl scripts can be used, which then allow, for example, links to other databases or perform special tests.

The currently latest version 4 has been completely revised and made ​​possible by an access control list system very accurate and flexible configuration to prevent spamming. Different plug-ins also allow for a review of the content of e- mails for computer viruses, spam, and unwanted files.

On December 7, 2010, a severe vulnerability of Exim has been reported, obtained by the attacker unrestricted access to the system.

Exim 4 is the default MTA on Debian GNU / Linux.