Just every now and then I'll get a call that someone can't login to their email in Outlook even though they are sure they are using the right password. The solution is simple, the answer 9/10 times is that the username in Outlook has randomly changed from "email@example.com" to "firstname.lastname@example.org" (I think that's how it comes out, I know it uses our company name instead and I've seen it add the domain name in there as well). Once the user changes it back to what it is supposed to be, they can login. At first I ignored it, but it just keeps happening. I've contacted our parent company but they've said it's got to be a problem on my end.
Our parent company manages our email exchange server (Exchange Server 2010) and I manage our Active Directory domain here. On the user computers the account is setup to Connect to Microsoft Exchange using HTTP.
It seems that the problem only started happening after I setup our company as a domain (it was a workgroup previously). So somewhere and only occasionally it seems that Outlook gets confused about what email account it is trying to connect to (even though there is only one).
I've checked the Windows user credentials on some of the user's computers that are having this issue and there is none.
I've checked the settings in Active Directory because some users had old exchange server settings left over from when we managed our own exchange, but that doesn't appear to be the problem either because newer users that have never hooked into out internal exchange server also have this message appear.
I'm looking at possibly installing the Outlook/Office Group Policy settings, but I haven't found yet if it will have a policy option that will be of any use to me. When I google the issue I get lots of different issues, but I haven't found any good resolution yet.
Any ideas? (I'm not afraid to say I'm still new to system administration, I'm learning on the job and have only been at it for about a year now)