I noticed there was an update avalable for Logwatch (7.3.1) recently and it now puts percentages in the report for amavisd-new hits. I’d not thought of pulling the statistics for my ickle mailserver untill I noticed quite how depressingly high my spam quotient is.

6402            Scanned
614 ( 9.59%)    Clean passed
130 ( 2.03%)    Malware blocked
5638 (88.07%)   Spam passed
2 ( 0.03%)      Banned file names passed
18 ( 0.28%)     Bad headers passed
26              Headers without subject line