Mailgraph creates daily, weekly, monthly, and yearly graphs of sent, received, bounced, and rejected emails and also of spam and viruses, if SpamAssassin and ClamAV are integrated into Postfix
Read it here at Howtoforge
In the following I will describe how to install and configure Mailgraph and pflogsumm on Debian Sarge, Ubuntu Dapper Drake (6.06 LTS), and Fedora Core 5.
I want to say first that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!