submission port ist mit heutigen releases verfügbar per default (nach deployment durch grommunio-setup).
für alle, die submission nachträglich für bestehende installationen aktivieren wollen:
postconf -M submission/inet="submission inet n - n - - smtpd"
postconf -P submission/inet/syslog_name="postfix/submission"
postconf -P submission/inet/smtpd_tls_security_level=encrypt
postconf -P submission/inet/smtpd_sasl_auth_enable=yes
postconf -P submission/inet/smtpd_relay_restrictions=permit_sasl_authenticated,reject
postconf -P submission/inet/milter_macro_daemon_name=ORIGINATING
systemctl restart postfix
firewall-cmd --zone=public --add-port=587/tcp --permanent
firewall-cmd --reload