Last Updated: June 18, 2018
When you try to connect Outlook 2016 MSI (Volume License) to a SharePoint Online calendar it fails to connect with repeated authentication prompts.
The SharePoint team made a service change on 14 June 2018 to mitigate the issue. It may be necessary to restart Outlook for the change to take effect.
Now that the fix has released please reference the workaround below and delete the EnableADAL registry key.
Click Windows Start + R and type regedit
Paste Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity into the address bar at the top
Double click EnableADAL and edit the Value data to 0
WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved.
Before making any change in the registry, please back up your Registry.
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