Use multiple filters
(Evaluating SpamAssassin without its Bayes feature
enabled is probably non-useful. Who would do that?
The question is, what slips past SA with Bayes turned on?)
I run four spam filters. The combination gets just about
everything. First is a short blacklist of repeated spammers. Then
SpamBouncer (www.spambouncer.org), SpamAssassin with Bayes enabled, and simple filtering on the last
hop before the mail was delivered to my ISP. (90% of all spam is
sent from servers that either have no reverse DNS or are
identified as a dialup, cable, or DSL line.)
Every day, I get some spam that is caught by only one of these
filters. Since I got the last three set up, I get one or two false
negatives a month: i.e. spam seen as legitimate. I see a few pieces of
mail a month that get false positives until whitelisted. Last
month I got over 17,000 mail messages, 95% spam, and the
percentage is gradually rising every month.
The spammers and the filters are in a continual arms race.
Whoever commits first loses: you can filter any fixed kind of
spam, and you can design messages to evade any fixed filter.
But the delay in designing filters will leave some incentive
for spammers, and the rising cost of filtering may eventually
cause some people to give up.
As one of the first creators of an email program I am saddened by
its misuse. See www.multicians.org/thvv/mail-history.html
for what I remember.