Recommended Mail Transfer Agent

[Michael Madden]

I'm looking to setup a mail server with FreeBSD 5.3 for a group of around
100 users, and I was wondering which MTA I should use.  I have noticed 
sendmail is the default MTA, but I have no sendmail experience.  Also I know 
historically sendmail has had some serious security issues.

Furthermore, can someone recommend a decent POP3 and IMAP server?

Thanks in advance,
Mike