Special Outlook problem

Shortly after installing a new Office 2016 (Click to run) on a new Windows 10 PC, Outlook - already connected to an Exchange 2016 server in a domain - began to ask for user and password - although Outlook showed "Connected to Exchange" at the bottom of the window.
This happend a few seconds after Outlook was started, and one or the other time during the day.

For the first moment the Problem could be solved by clicking "Cancel" in the window that asked for the login credentials, and then by clicking on "Enter Password" at the bottom of the window - and Outlook was working for some Hours without further asking.

Fortunately I found this article (https://social.technet.microsoft.com/Forums/en-US/b57ee243-2545-4ad8-81a5-7c005e4cf6ec/outlook-2016-repeatedly-asks-for-password-and-none-of-the-fixes-i-have-found-are-working?forum=outlook), solving the Problem in my case, by adding an unexpected registry entry.

I had to add/find this key

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover
(16.0 corresponds to the Outlook version: 16.0 = Outlook 2016)

and add this new DWORD ExcludeExplicitO365Endpoint, and give it the value 1

And voila - after restarting Outlook the problem was gone :-) !

Helped me, and I hope it helps anyone else !