debug SMTP commands sent/received to/from the submission service

Dear Colleagues,

I'm trying to debug SMTP commands clients send to the submission service.

I've tried

protocol submission { rawlog_dir = /var/tmp/dovecot }

but /var/tmp/dovecot remains empty. What am I missing? I'd use Wireshark but the communication between SMTP clients and Dovecot is encrypted after STARTTLS, so Wireshark is pretty useless here.

Can you please point me to the right direction to log all SMTP commands? All is happening on Debian/buster, Dovecot 2.3.4.1.

-- Victor Sudakov VAS4-RIPE http://vas.tomsk.ru/ 2:5005/49@fidonet