We rolled out Office 2019 Professional to around 50 of our employees. A select few are not experiencing any issues, which includes me. This means all tests before the roll-out worked just fine. After rolling out to the rest of our IT department, we had the first issue, our colleague was prompted to fill in his password. After some trial and error, we found out that the emails will still download if you just close the "Windows Security" prompt. The new problem was that it would not stop popping up every few minutes. This popup can be delayed by pressing the "Need Password" button in the bottom right-hand corner of Outlook after closing the prompt the first time (It will only pop up when starting Outlook the first time in that case).

We decided this was a one time issue and we can for now just ignore it and roll out to the first wave of employees. During this roll-out, we experienced the next problem. With another hand full of users Outlook will prompt for a password and username in the setup process. This can be skipped by closing the prompt pressing retry and closing the prompt once more. Now we have the same issue as for my colleague.

Concluding: Only with the right combination of user account and PC, Outlook will not prompt for the login.

What could be causing this issue and how can it be dealt with?

We have tried multiple things for debugging:

  1. Delete local files, this helps until the next restart.
  2. Adding a DWORD Registry entry in Computer\HKEY_CURRENT_USER\Software\Microsoft\Exchange called "AlwaysUseMSOAuthForAutoDiscover" and setting the value to "1" will open and "Let's get you signed in" window. When trying to log in here it says "Are you sure that's the right email address? This organization doesn't support joining Azure AD."
  3. Instead of using username@network we used the email address, this has no effect at all.
  4. Under the user identification the “Always prompt for logon credentials” is not checked.
  5. Checked user configs in Active Directory with mine and other working ones, could not find any difference.

Adding a "DWORD" Registry entry in "Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover" called "ExcludeExplicitO365Endpoint" and setting the value to "1" solved the issues we were experiencing.

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