To help improving the spam filtering, I train Spam Assasin with what I think is spam based on what’s in the Junk and Spam folders in any mailbox, I run the following command in the crontab:
@daily sa-learn --ham /srv/*/mailboxes/*/Maildir/ && sa-learn --spam /srv/*/mailboxes/*/Maildir/.Junk/ /srv/*/mailboxes/*/Maildir/.Spam/
The ham teaches it what’s good, the spam teaches it what’s spam. If a message moves from one to the other it get re-trained as appropriate.