split auth from other logging

Is there a way to split the auth logging (logins and failed logins) from the other logging that goes to info_log_path = /var/log/dovecot/dovecot.log ? This log gets a lot of other info as well, most notably the lmtp notifications about every filed mail (with no level stamping, btw). This makes it really hard to find authentication errors quickly and comfortably. It would be nice to be able to split at least the lmtp messages away.

Kai