This settings defines the TCP/IP port which Lyris listens on for incoming mail. By default, this setting uses port 25 that is the Internet standard for receiving SMTP mail.
In some situations, you may want to move the Lyris SMTP service to another port. Perhaps you already have a service on port 25, and you do not want the services to conflict over the port assignment.
In such a case, you will need to configure your mail system so that mail that Lyris should get is forwarded on to Lyris at its port. For instance, you might create an alias (a DNS CNAME) for Lyris
mail, and inform your mail system that mail addressed to this alias should be passed on to Lyris on this port assignment.
Note that if you change this port number, and don't work out an alternate way for Lyris to get its mail, that Lyris will no longer be able to receive mail, and any mail sent to Lyris from the outside
will not reach it.