cp /etc/letsencrypt/live/[cert path]/privkey.pem /etc/dovecot/privkey.pem
cp /etc/letsencrypt/live/[cert path]/fullchain.pem /etc/dovecot/fullchain.pem
chmod o+r /etc/dovecot/privkey.pem /etc/dovecot/fullchain.pem
/etc/init.d/dovecot restart