I work in Microsoft Social Media and I received the following link to a question from one of our users. The link is as follows: http://serverfault.com/questions/425152/whats-the-meaning-of-logging-in-as-usernamemydomain-comsomething The question within it is below: "My Windows 2008 R2 machine is joined to a domain. In the logon screen, if I type in "username@mydomain.com:something" as the username, I can still logon properly, what's the meaning of ":something" appended at the end? I can even see the current user is displayed as "username@mydomain.com:something" in the switch user screen. Is it a feature in Windows? Or is it just a bug? If it is a feature, what's the difference between logging in as "username@mydomain.com" and logging in as "username@mydomain.com:something"? Note that I tried different combinations like "mydomain\username:something" and "mydomain.com:something\username". None of them work except "username@mydomain.com:something"." I've underlined the specific question. Please post if you know what this means. Thanks Social Media - Dwayne W

My 2 cents here: The format user@domain:something could indicate a specific port/service mapping, like domain.com:443 for SSL, but as I said, only what I think this could be, not sure if this is the purpose. No explanation found here: http://msdn.microsoft.com/en-us/library/windows/desktop/aa380525(v=vs.85).aspx, where it should be... I tested it in my domain with strange port/name combinations and it works... I guess maybe an unsupported feature, but accepted user@domain:port/service? I let the experts answer it ;) pls vote as helpful if this piece of text helps you...Thank you, F. Schubert System Administrator MCP | Microsoft Certified Professional MCTS 70-640 | Microsoft Certified Technology Specialist: Windows Server 2008 Active Directory, Configuration MCTS 70-642 | Microsoft Certified Technology Specialist: Windows Server 2008 Network Infrastructure, Configuration

No, This does not help. We did all of this same testing over at ServerFault as originally posted but no one seems to know what's going on with this stuff. Thanks, Brent

This is not the answer (despite being marked as one). The actual answer, according to MS premier support, is here, at the ServerFault thread. (Not a bug, or feature, but a result of the way usernames are validated, on the back end.)