I don’t know why I didn’t think of this earlier. My email is stored on an IMAP server and I primarily used Apple’s Mail.app client to access it there. I’ve got Mail.app set up to store mail it identifies as “Junk” on the server, but until today I wasn’t harnessing Mail.app’s junk-fighting skills to make SpamAssassin smarter.
All I needed to do to make this happen was to set up a cron job to have SpamAssassin learn that all the mail in the Junk folder was spam:
/usr/bin/sa-learn --spam /home/peter/Maildir/.Junk/cur
This simply tells the SpamAssassin “learning” application, sa-learn, to take all the mail in my Junk folder and learn that it’s spam. I run it one a day.