33.4 Firewall/Router Configuration
Since the sending and receiving of email messages involves network connections, the firewall will need to be configured to allow SMTP traffic. If firewalld is active, use the firewall-cmd tool will as follows:
# firewall-cmd --permanent --add-service=smtp
Alternatively, if ufw is enabled, configure it to allow SMTP traffic using the following command:
# ufw allow Postfix
It will also be important to configure any other firewall or router between the server and the internet to allow connections on port 25, 143 and 587 and, if necessary, to configure port forwarding for those ports to the corresponding ports on the email server.
With these initial steps completed, we can now move on to installing Postfix.