At a Redstor partner or customer using self-hosted storage, a backup of Exchange mailboxes fails with the following error:
Error: Code: generalException Message: Unexpected exception returned from the service.
Recurrent 503 and 504 error codes are also seen in App Insights.
An HTTP 503 response (Service Unavailable) typically indicates a performance issue on the server, while HTTP 504 (Gateway Timeout) indicates that the server did not receive a response in time to complete the request.
To resolve this, restart the StorageServer service and run the backup again.
Note: This issue should not affect users on Redstor hosted and managed storage, as the operational and connectivity status of this is closely monitored.