Test-OAuthConnectivity fails from on premises exchange to O365

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&nbsp;I ran HCW and it completed successfully but at the end it gave warning that OAuth could not be setup please re run the HCW or try setting up OAuth manually. I re ran the Oauth still same issue hence followed the steps mentioned in the TechNet&nbsp; articleAfter successfully following al the steps I tried to test the OAuth connectivity from on premises exchange to office 365 by running the command:&nbsp;Test-OAuthConnectivity -Service EWS -TargetUri https://outlook.office365.com/ews/exchange.asmx -Mailbox &lt;On-Premises Mailbox&gt; -Verbose | Format-List&nbsp;Got the error below:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;RunspaceId&nbsp; : 33d7dd07-9028-40f8-bfa9-1f8ed554765gfTask&nbsp; &nbsp; &nbsp; &nbsp; : Checking EWS API Call Under OauthDetail&nbsp; &nbsp; &nbsp; : The configuration was last successfully loaded at 01-01-0001 00:00:00 UTC. This was 10923476 minutes ago.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; The token cache is being cleared because "use cached token" was set to false.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Exchange Outbound Oauth Log:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Exchange Response Details:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; HTTP response message:&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Exception:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.Net.WebException:&nbsp;The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. ---&gt;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.&nbsp;&nbsp;When testing the OAuth connectivity from O365 to exchange server it is successful.Any help would be appreciated&nbsp;

serverpro · Accepted Answer

PeterRising&nbsp;thanks for your help..The issue was due to the firewall blocking office 365 ews . I allowed the URL in F5 firewall and it resolved the issue&nbsp;

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Test-OAuthConnectivity fails from on premises exchange to O365

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