Charles reports that Mail.app only catches 20% of his spam. It catches about 80% of mine. Maybe the filtering database has gotten fowled somehow.
The success rate varies for me. For a while base64 encoded html attachments were getting through. But I dutifully flagged them as junk and Mail seems to be catching them more consistently. In some recent mutations spammers are *M *E *S *S *I *N *G with words in the subject line and adding random noise fdxciqwea.
The virus mutates. The new strain is virulent until the antibodies in the population develop and correct the imbalance. The pattern is the same whether the virus is SARS, or CodeRed, or the NPR funding hoax.
The first Mail.app preference I turned off was 'Display images and embedded objects in HTML messages'. Hit counts for links to images provide spammers with immediate feedback about which mutations are surviving spam filters in the wild. Unfortunately, there are enough mail clients providing that feedback that the spammers can breed the mutations which are most effective at evading filters.
Now if only I could get a bayesian filter installed on my snail-mailbox.