OAuth authentication is removed when you save MAPI virtual directory settings in EAC in Exchange Server 2019 and 2016

Symptoms

Consider the following scenario in a Microsoft Exchange Server 2019 or Exchange Server 2016 environment:

You check the MAPI virtual directory by using the Get-MapiVirtualDirectory cmdlet and notice that the OAuth authentication is enabled.
You open Exchange Admin Center (EAC), double-click the MAPI virtual directory and don't change anything, and then click Save to close the window.
You run the Get-MapiVirtualDirectory cmdlet to check the authentication methods.

In this scenario, the OAuth authentication will be disabled.

This issue occurs because Exchange Server incorrectly removes the OAuth authentication when you click the Save button in EAC.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

To fix this issue, install one of the following updates:

For Exchange Server 2019, install the Cumulative Update 1 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.

For Exchange Server 2016, install the Cumulative Update 12 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.

Learn about the terminology that Microsoft uses to describe software updates.

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