Outlook Mobile App users have recently encountered issues connecting to Exchange 2010. This article provides a comprehensive guide to diagnosing and resolving this issue.

Problem: RPC over HTTP Support Removed?

Outlook Mobile Apps on Android and iOS devices have ceased functioning for numerous users, presumably following an Outlook update. Despite the Outlook Web App (OWA) and Microsoft Remote Connectivity Analyzer showing no problems for Active Sync and Outlook connectivity tests, attempts to set up Outlook on Android phones have been unsuccessful.

Possible Cause

One possible explanation is the removal of RPC over HTTP support, leaving only MAPI over HTTP. This could potentially cause compatibility issues with Exchange 2010.

• Microsoft may have removed RPC over HTTP support, leaving only MAPI over HTTP.
• This change could be the culprit behind the Outlook mobile app malfunction.

Diagnosis and Troubleshooting Steps

When attempting to connect to the client’s Exchange server from an Android phone, no connection attempts were observed on port 443 of the router or Exchange server. Furthermore, no relevant entries were found in the Exchange logs.

• Check the Microsoft Remote Connectivity Analyzer for any issues.
• Verify that the Exchange server is receiving connection attempts.
• Review the Exchange logs for any errors or authentication failures.

Error Messages and Clues

• Error occurred during authentication. Please try again later.
• Unable to login. Please check your email and password and try again.
• “Audit failure” event in Exchange log, citing unknown user name or bad password.

The Likely Cause: Authentication Method Incompatibility

• Outlook mobile apps may be attempting an authentication method not supported by Exchange 2010.
• The issue could be related to Microsoft servers connecting to the on-premise Exchange server.

Solution

Upon inspecting the IIS logs, records of a connection from a Microsoft server were found. The IP address, 52.96.192.85, was previously on a block list and has since been unblocked.

However, users are now encountering an “Unable to login. Please check your email and password and try again” error message. An “audit failure” event was also observed in the Exchange log, indicating an unknown username or bad password.

It appears that Outlook on Android is attempting an authentication method not supported by Exchange 2010. If Outlook connects from an Android phone to a Microsoft server, which then connects to Exchange on-premise, the issue likely lies outside of Outlook.

To resolve this issue, follow these steps:

1. Open the Exchange Management Console.
2. Navigate to Server Configuration > Client Access > Exchange Active Sync > Authentication.
3. Select the “Accept Client Certificates” option.

This change should allow the Outlook Mobile App to authenticate successfully with Exchange 2010.

Conclusion

By following the steps outlined above and enabling client certificate authentication, users can regain access to their emails on-the-go.

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