Symptoms
If you change the MAPI virtual directory URLs by using the Exchange Admin Center (EAC), all forms of authentication are removed from the MAPI virtual directory.
Resolution
To fix this issue, install Cumulative Update 4 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.
