For each service, you can specify the port number that the server is to use for service connections:
If you enable the POP service, you can specify the port number that the server is to use for POP connections. The default is 110.
If you enable the IMAP service, you can specify the port number that the server is to use for IMAP connections. The default is 143.
If you enable the HTTP service, you can specify the port number that the server is to use for HTTP connections. The default is 80.
You might need to specify a port number other than the default if you have, for example, two or more IMAP server instances on a single host machine, or if you are using the same host machine as both an IMAP server and a Messaging Multiplexor server. (For information about the Multiplexor, see Chapter 7, Configuring and Administering Multiplexor Services.
Keep the following in mind when you specify a port:
Port numbers can be any number from 1 to 65535.
Make sure the port you choose isn’t already in use or reserved for another service.