Some users are receiving bounce messages when they send to external recipients:
The server has tried to deliver this message, without success, and has stopped trying. Please try sending this message again. If the problem continues, contact your helpdesk.
#550 4.4.7 QUEUE.Expired; message expired ##
Review the Queues under Tools in Exchange Management Console.
You find some messages are stuck in the queues on your Exchange 2010 server, and the error reads: “A storage transient failure has occurred during content conversion”
Cause: There is a queue/transport bug when running Exchange 2010 SP3 Rollup 1 on Windows Server 2012.
Background: I contacted Microsoft Product Support Services to see if there was a hotfix available. The Support Engineer explained that no hotfix was available, however this issue would be fixed in SP3 Update rollup 2 available in September. In the meantime a workaround is available:
Note: TNFEEnabled is set to Null (‘blank’) by default.
after changing the TNFEEnabled setting, I restarted the Microsoft Exchange Transport Service for good measure.
additional findings: Changing the Message Format for the Organization to ‘Determined by individual user settings’ (Organization Config -> Hub Transport -> Remote Domains -> Default -> Message Format) and then configuring the users Outlook who have the stuck messages from RTF to HTML stops their messages from getting stuck in the queue. Note: changing the organization Message Format setting will revert the TNFEEnabled setting back to default ‘Null’ (blank).