Just discovered this:
http://www.officesip.com/howto-windows-messenger.html
I didn’t know there was a way to connect this version to a SIP server…
Yeah, Windows Messenger (some versions of?) can also connect to an Exchange server, for what I believe is internal messaging purposes? I’ve not really bothered to look into it, but I guess those features are useful if you have (had) Microsoft infrastructure.
Windows Messenger’s SIP support wasn’t limited to Microsoft’s Live Communication Server (later, Office Communicator, then Lync, now Skype for Business) but compatibility was always a problem.
Also, this feature is separate from Exchange; the Exchange Instant Messaging (from Exchange 2000) is its own protocol and separate from SIP. Windows Messenger 5.x supports all 3 - .NET Messenger, SIP Communications and Exchange Messaging.
I remember reading a Microsoft document where it was stated that Windows Messenger was intended as a business software and MSN Messenger was a consumer version.
They probably kept the 2 paths: Windows Messenger became the Communicator client and MSN Messenger continued its way…