Although this issue has been around for a while, it seems more prevalent with Microsoft discontinuing Basic authentication. The pop up screen screams Basic authentication and not Modern authentication.
Basic issue is that you can’t seem to get Outlook to accept its password, you’ve tried the App key etc. and nothing. Creating a new profile does nothing.
I’ve seen different ways of dealing with this but it all boils down to one reg key
- HKCU\SOFTWARE\Microsoft\Office\15.0\Common\Identity (could be 16.0)
- Look for a DWORD key called EnableADAL
- If the value is 0, change it to 1 and test
- If the value is 1, change it to 0 and test
- If all else fails, delete the DWORD