For years I’ve fought spam with all sorts of techniques, some limited server side tricks in setting my postfix rules to very strict adherence and using RBLs, but ultimately settling on whitelist filtering on my Trusty Eudora client, POPping all that spam over whatever airport international dialup I happened to be on and cursing it even as it disappeared into the UBC folder for bulk deletion.
And I dreamed of the day when I would switch to IMAP and set up all those cool anti-spam server-side techniques I’d been reading about, primarily SpamAssassin. The problem with spam filtering is that it often catches your friends.
So I found this great procmail filter that whitelisted on the server side and sent confirmation requests to unlisted addresses. So I installed Procmail on my server, then SpamAssassin, and rewrote the filter below to do just what I wanted: