Comment 17 for bug 827151

I don't think that changing the logcheck regexp will help here. The logcheck program doesn't actually prevent messages from being logged to syslog. All it does is scan the existing logs and optionally alert on certain types of messages. The /etc/logcheck/ignore.d.server/libsasl-modules file will prevent logcheck from alerting on certain messages, but the messages are still there in syslog. See the logcheck man page for more info:

http://manpages.ubuntu.com/manpages/focal/man8/logcheck.8.html