I used to use this for antispam filtering, but it made evolution pretty slow when clicking send/receive, if I happened to have received a lot of new mail - So I've gone back to spam filtering via procmail now that our mail server handles load better. This method does, however, have the attribute of doing the filtering on the machine you're running evolution on though, instead of the machine that delivers the mail - sometimes that's better, sometimes that's not.

So here it is: