Exim is a mail transfer agent for Unix systems connected to the Internet.

 .   Exim is intended for use as an Internet mailer, and therefore handles
     addresses in RFC 822 domain format only. (No bangpaths!)

 .   The only external transport currently implemented is an SMTP transport
     over a TCP/IP network (using sockets). A pipe transport is available,
     and this could be used to send messages to some other transport mechanism.

 .   Exim is very configurable, and its management is very powerful. It can
     be configured to be "fussy" about certain hosts or domains, and
     can easily serve multiple domains.

 .   Exim is an excellent mailer for an ISP, as its control and flexibility
     are very good.

 .   Its requeuing and retry algorithms are very powerful.

WWW: http://www.exim.org/