Turn on debug mode in Dovecot

Don't know where Amavisd config file is? check this tutorial: Locations of configuration and log files of mojor components.

To turn on debug mode in Dovecot, please update below parameter in Dovecot config file dovecot.conf:

mail_debug = yes

Restart Dovecot service.

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