How to recover mail (Postfix + Dovecot)

systemctl status postfix dovecot opendkim --no-pager
journalctl -u postfix -n 40 --no-pager
journalctl -u dovecot -n 40 --no-pager
sudo systemctl restart postfix dovecot
ss -lntp | egrep ':(25|143|587|993)\b'

LDAP users feed mail auth via OpenLDAP — if auth fails broadly, check slapd / nslcd too.

systemctl status slapd nslcd --no-pager