dovecot

one config file is

 /usr/share/dovecot/dovecot.conf

2023-01-27: disable pop3 by commenting it out in /usr/share/dovecot/protocols.d/pop3d.protocol

... and restarting with systemctl restart

SSL

The configuration is in

 /etc/dovecot/conf.d/10-ssl.conf

The cert is created / refreshed with:

 certbot certonly --webroot -w/local/bonmot/ -d mercury.bonmot.ca
 systemctl restart dovecot

The keys are in cert & chain /etc/letsencrypt/live/mercury.bonmot.ca/fullchain.pem key file: /etc/letsencrypt/live/mercury.bonmot.ca/privkey.pem