With mailgraph you can make really cool graphs to visualize daily, weekly, monthly and yearly statistics about postfix received/sent and bounced/rejected/spam/virus mails.
Some days ago I started to use postfix's postscreen feature. I didn't thought how cool and useful is. The spam volume is reduced with more than 50% on my server.
But I like very much graphs with mail statistics, I need postscreen stats too. Google it, but found nothing with separated stats, only cumulated with reject or spam.
So I made a patch based on NetworkMonkey IT Blog and if you use postfix with long queue id, you need to apply another patch to mailgraph from here: http://pub.birkosan.com/mailgraph/long_queue_ids.patch.
You need to patch mailgraph.pl and mailgraph.cgi too!