spamd[8917]: plugin: eval failed: bayes: (in learn) locker: safe_lock: cannot create lockfile user@domain.pl/.spamassassin/bayes.mutex: No such file or directory

How to fix:

mkdir /var/qmail/bayes
chown popuser:popuser /var/qmail/bayes
chmod 770 /var/qmail/bayes

mkdir /var/spamassassin
chown popuser:popuser /var/spamassassin
chmod 770 /var/spamassassin