Ok, got the postfix/dovecot solution up and running, and it's performing nicely. It's a definite upgrade from the Windows 2003+SMTP server solution that was there before, performance is not comparable, and management with the postfixadmin is just simply nice. Again, thankyou very much to everybody that helped with that.
I would like to add a solution for antivirus, we have Symantec corporatewise, but compiling the SEP on CentOS doesn't really work well, so I was thinking about going with ClamAV.
Now the integration to postfix is the question, I JUST need the antivirus, not spam filtering or anything like that, so I guess something like Amavis-new is overkill.
But what else is good, and maintained out there, and easy to keep updated?