Proper way to enable statistics on Dovecot 2.3.20?

Hi.

I'm using Dovecot on OpenBSD OS. "dovecot --version" reports: 2.3.20 (80a5ac675d) and this is my configuration file: https://termbin.com/m4to

How to properly set the statistics for the version I use? I have both "service stats" and "service old-stats" and it seems I'm not really getting any statistics. Where's my mistake? Thanks in advance. ("doveadm oldstats top" command gives an empty page with columns.)

Thanks.