The ServerPort property is used to set the port number that
server will use to listen for incoming client connections. Valid port
numbers are in the range of 1 to 65535. It is recommended that most
custom servers specify a port number larger than 5000 to avoid
potential conflicts with standard Internet services and ephemeral
ports used by client applications. The default port number for
standard connections is 21.
If a port number is specified that is already in use by another
application, the OnError event will fire and the background
server thread will terminate. Attempting to change the value of this
property after the server has started will cause an exception to be
raised. To change this property value, you must first call the Stop
method which will terminate all active client connections.