1) Go for Postfix it is easy to use and configure
2) Go for SpamAssassin, a powerful open source spam filter
http://spamassassin.apache.org/
3) Go for clamav
http://www.clamav.net/ virus scanner, you can also use commercial anti virus for your mail server such as McAfee or others
4) You also need to setup IMAP and POP3 server such as dovecot
http://www.dovecot.org/ or Cyrus IMAP
http://asg.web.cmu.edu/cyrus/imapd/
5) Postfix Howtos and FAQs
http://www.postfix.org/docs.html
If you have any other question related to configuration feel free to ask here and we will assist you.
__________________
Rocky Jr.
You may have my body & soul, but you will never touch my pride!
If you have knowledge, let others light their candles at it.
Certified to work on
HP-UX /
Sun Solaris /
RedHat