Very recently some my clients began experiencing a troubling problem: while using Outlook 2011 on Mac OS X, they were constantly getting prompted for a password, stating that the old password was incorrect. Now, having experience with that kind of thing before, the first thing I checked was that their account was not getting locked out somehow (usually due to too many incorrect password attempts). But in this case, that was not the problem.
Next, I simply had them shut down Outlook completely and start it up again. Sometimes programs get unstable when left running for too long. It shouldn’t happen, but it does. And this is Microsoft software on a Mac so it seems par for the course. But still the problem continued.
Then I checked the Keychain, which is a utility on the Mac that stores authentication for different programs in a central place. I checked it for errors, fixed the ones it found, and when even that didn’t work, I wiped out the old entries and created new ones. Still the problem continued.
Eventually while digging in Google, I came across the solution.
For some unexplainable reason (or at least not any reason Microsoft has made public), instead of the usual email@example.com username format, Outlook 2011 requires the following:
So for example, let’s say your domain is contoso.com and your username was alfred. In that case, when setting up your account settings, you would input this in the username field:
For my client, it had worked before fairly consistently with the old firstname.lastname@example.org username, but after an update or when upgrading to OS X 10.10 Yosemite, or some other mysterious combination of circumstances, this issue appeared.
I hope this helps others — I really had to dig to find this gem.