Have you tried /var/log/syslog?
Per the Dovecot official wiki (with a literal 2 second google search mind you 
):
By default Dovecot logs to syslog using mail facility.
Have you tried /var/log/syslog?
Per the Dovecot official wiki (with a literal 2 second google search mind you ):
By default Dovecot logs to syslog using mail facility.