4.7. Submission port

Many ISPs today block port 25 for users. To be able to send email using our Postfix mail server as our outgoing server, we need to enable submission port (port 587) in Postfix and change the firewall rules to allow traffic to port 587.

Open /etc/postfix/master.cf and uncomment the following lines:

submission inet n       -       -       -       -       smtpd
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

Spaces in the lines after the first line are important. Do not delete them!