I’ve run where I work for 4 years a Mandrake based firewall with Postfix and Mailscanner. I really, really liked mailscanner, but for my colleagues the setup was “too complicated”. So I moved to EFW, Endian Firewall comunity edition. What it brings in ease of use it lacks in flexibility.
Finally my prayers where listen, and I’m going to move again to a custom build full fledged mail gateway with Mailscanner. Check out: this howto.