Exchange: An unknown error has occurred. Refer to correlation ID: <Removed PII>

The error message you are encountering, "Exchange: An unknown error has occurred. Refer to correlation ID: 948ed9db-d921-4bc0-be7d-e02365f32a4f," typically indicates an issue with the synchronization process between your on-premises Exchange and Exchange Online. This can occur for various reasons, including license issues, mailbox holds, or problems with the user profile configuration.

To troubleshoot this issue, consider the following steps:

1. Check User Licenses: Ensure that the user has the appropriate Microsoft 365 or Office 365 license assigned. If the license was recently unassigned, it may cause synchronization issues.
2. Mailbox Hold: If the user's mailbox has a hold applied, it may prevent the mailbox from being disconnected properly when the license is unassigned. This can lead to errors during synchronization.
3. Directory Synchronization: Verify that directory synchronization is functioning correctly. You may need to manually force synchronization to see if that resolves the issue.
4. Review Correlation ID: Use the correlation ID provided in the error message to look up more detailed error logs in the Microsoft 365 admin center or Exchange Online logs. This can provide more context on the specific issue.

If these steps do not resolve the issue, consider reaching out to Microsoft support for further assistance, as they can provide more detailed diagnostics based on the correlation ID.

References:

• Errors after unassigning a user license

Hi @Jeevan PK

Thank you for posting your question in Microsoft Q&A. 

Based on my research, the response message ‘Exchange: An unknown error has occurred. Refer to correlation ID’ can be triggered by multiple underlying factors. 

However, as your description, it’s likely related to incorrect or missing Exchange attributes on the user object. To investigate it, you could follow these steps: 

Validate Exchange Attributes 

Run the following commands in PowerShell to review the mailbox and user properties: 

Get-Mailbox <UserPrincipalName> | fl 
Get-User <UserPrincipalName> | fl 

Reset Password and Sync 

Reset the user’s password in Active Directory, allow it to synchronize to Microsoft 365, and then retry the operation. 

Confirm Licensing 

Ensure the Exchange Online license is correctly assigned to the user’s account. 

If possible, please share the log details or a screenshot of the issue. This will help me identify it more effectively. 

If you have any additional concerns, feel free to comment below. I would be more than happy to assist. 

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