Out of the blue today my email started filling with spam that I normally don’t see. A quick look at the headers showed a notable lack of a bayes score from spamassassin. Hmm.
A look in /etc/mail/spamassassin/local.cf shows no change, with the option to use bayes turned on.
I took a look a the directory mentioned in the second config line and saw that the files bayes_journal and bayes_toks were both owned by root instead of my amavis user. I checked my backup files and sure enough, they should be owned by amavis (user and group). Now, I have no idea how the change happened, but nevertheless this command:
chown amavis.amavis /var/spool/amavisd/.spamassassin/*
has fixed the problem.