Test-OAuthConnectivity always fails when Exchange Server uses proxy to connect to Internet in Exchange Server 2019 and 2016

In Microsoft Exchange Server 2019 or Exchange Server 2016, assume that you set a web proxy server that the Exchange Server uses to reach the Internet by using the InternetWebProxy parameter and there's no direct access to the Internet. You may experience that the OAuth connectivity always fails if you test it by using the Test-OAuthConnectivity cmdlet even if the connectivity is working fine. 

This issue occurs because the Test-OAuthConnectivity cmdlet does not honor the InternetWebProxy settings set on the Exchange Server. Therefore, if the Exchange Server is blocked to connect to the Internet directly, you won't correctly test the OAuth connectivity.

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

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