When using Exchange 2010 there could be a moment where a message gets stuck in the message queue with the message: ‘A storage transient failure has occurred during content conversion‘.
This is due to a transport/queue bug in Exchange 2010
The solution (more like a workaround) seemed quite simple: just enable TNEF.
You can do this in Powershell with the follwing command:
Get-RemoteDomain | Set-RemoteDomain -TNEFEnabled $true
The message that was stuck went through immediately when this was enabled.
However after a few days there were complaints about getting mails without wrong attachements, they would get an attachement like winmail.dat.
This was due to TNEF being enabled, so the ‘solution’ made a new problem.
So the final option seemed to be installing latest updates. The exchange services were never been updated.
At the moment the latstest update was CU15 (you can download it here).
Installing these updates and disabling TNEF have solved both problems.