Today I configured Cacti and SNMP after I saw the graphs of a friend. He had graphs for Postfix, which showed statics like sent/received/rejected.
After a little search on the internet, I found a post on the Cacti forum. At first I couldn’t get it to work, but after running the script manually (instead of via SNMPd) I found out /var/log/mail.log was not readable by the SNMP user.
Cacti has been polling snmp for the past few hours now and apparently I receive around 25 spam emails that get rejected every 5 minutes. That’s 6000 mails per day, more than 2.000.000 every year. I’m glad I configured postfix to reject those mails (have a look at the reject_rbl_client config directive of postfix).