AMS and port 627

In the article "Mac OS X Server 10.2's Apple Mail Server and UNIX' /var/mail", I read the following : "If you are running Mac OS X Server 10.2, you now have two options for passing mail from Exim, or any other mail transfer agent, to the Apple Mail Server. The "old" way was for the MTA (mail transfer agent?for example, Postfix or Exim) to make an SMTP connection to the localhost on port 627, where AMS would be listening. You can replicate this behavior in 10.2 by keeping the setting for AMS to use SMTP to transfer mail, but then manually set the incoming SMTP port to 627." How could I change "manually" the port of Incoming SMTP for AMS ? Thanks