I, and other people on my server, are having SPAM issues again. Spamassassin is great but it eats RAM for breakfast about the same rate it eats SPAM.

After some hunting I think I have found a solution:

Bogofilter is a mail filter that classifies mail as spam or ham (non-spam) by a statistical analysis of the message's header and content (body). The program is able to learn from the user's classifications and corrections.
Bogofilter Home Page

Happy SPAM munching.