Postfix greylisting policy service with auto-white-listing written in Perl with SQL database as storage backend. Greylisting stops 50 to 90 % junk mails (spam and virus) before they reach your Postfix server (saves BW, user time and CPU time).
Sqlgrey is perfect! Thanks.
Does what it says on the tin. Generally requires very little in terms of management or server resources.
I'm the main developer, of course I like it :-) Seriously, it gets the job done without getting in the way.