If you discover a bunch of old files in /var/mailman/qfiles/shunt, do NOT run unshunt. It doesn’t get rid of them, it delivers them to the mailing lists that they’d originally been rejected by since they came from non-members and are spam.
I just sent 18 peices of spam to the members of the Upstate Aviation Mailing list. And they’re all helpfully tagged ‘[UpstateAv]’ in the subject line so people know where they came from.