Exim

Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet. There is a great deal of flexibility in the way mail can be routed, and there are extensive facilities for checking incoming mail. Exim can be installed in place of sendmail, although the configuration of exim is quite different to that of sendmail.

Emuadmin is experienced in configuring and integrating with other open source software like the ClamAV virus scanner and spam filters, which are both very important these days, especially if you are serving Microsoft(R) Windows(R) clients.