#Turn on debug mode in Dovecot In __/etc/dovecot.conf__ or __/etc/dovecot/dovecot.conf__, change __mail\_debug__ to __yes__, then restart dovecot service.

mail_debug = yes

If you need authentication and password related debug message, turn on related settings and restart dovecot service.

auth_verbose = yes
auth_debug = yes
auth_debug_passwords = yes
auth_verbose_passwords = yes