add this line to /etc/syslog.conf and then restart (kill -1) syslogd:
auth.* -/var/log/zimbra.log
that will send the saslauthd logging there instead of nowhere. go ahead and post the output of these commands as well:
su - zimbra
zmprov getServer nobox.whatever.com | grep -e Mode -e Auth -e Port
cat ~/cyrus-sasl/etc/saslauthd.conf* |