What's your suggested mail server configuration for a FreeBSD server?
There are so many different possibilities here. What you're really talking about is an email "stack" (much like web-server/web-app "stacks").
- SMTP Agent a.k.a. MTA (Mail Transfer Agent)
There are several, including Sendmail, Exim, Qmail, Postfix, and Courier. Sendmail has had most of its "issues" resolved, Exim is small and stable, Qmail is fast, and Postfix is "flexible", sturdy, and fairly easy to configure. I guess it's a function of which one makes the most sense to you.
- IMAP/POP Backend
There are also several, including UW-IMAP (don't), and Dovecot (does POP3/IMAP, supports SSL). Courier also has POP/IMAP services.
Authentication Where to start? OpenLDAP is possible, but you can also get away with Kerberos, or even SASL.
Anti-Spam Tools Amavisd-new is a Perl script that hooks into SpamAssassin. Be sure to get the newest version(s) of both (the newer SpamAssassin supports detecting image spam via OCR).
Web Mail SquirrelMail has made the rounds, but Courier I believe also provides this.
...and...
- Anti-Viral Tools Clam is free and has a very good detection rate. If you use it with Amavis, it will act as a "backup" scanner. I have seen Clam detect things that commercial scanners won't (probably because the signatures are updated frequently).
My personal preference:
Postfix MTA, Amavis spam/virus filter, ClamAV scanner, Dovecot supplies IMAP over SSL, and SquirrelMail for a web interface.
I do have to admit that I don't run FreeBSD, sorry. However, I did take the time to check the BSD ports to see if all these package are available, and they are. So choose what you like. :)