Messenger Plus doesn't use any port becuse it doesn't connect to anywhere except for the following cases:
When looking to an update, it makes a HTTP connection to msgplus.net, so it connects to the port 80 of the server (the local port is a random one assigned by Windows).
When you use the (!IP) tag: The same as before.
When you use the POP3 check mail feature: It connects to a POP3 server, usually at port 110 (if you haven't changed it).
If you want to see which applications are making what connection and to what ports, you can use TCPView, from www.sysinternals.com
If you want more information about Messenger ports, read this
CookieRevised's reply to FileSend Ports
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