Hi Billy,
What steps have you tried so far?
What's the detailed version of Outlook 2016?
When do the prompt for credential window pop up? When we launch Outlook, or this occur in the middle when we use Outlook?
There is a Forum FAQ article: Why
does Outlook keep prompting for password
which introduces some ways to fix this issue. Please check if this is helpful to you.
If none of the steps work, we can try opening Outlook in safe mode to see if the issue continues. Please exit Outlook, press Win key + R to open
the Run command, type outlook.exe /safe and then press Enter. This helps eliminate whether the problem lies on any third party add-ins.
Any updates, please feel free to post back.
Regards,
Perry
Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact
tnsf@microsoft.com.

Click
here to learn more. Visit the dedicated
forum to share, explore and talk to experts about Microsoft Teams.