Exchange 2013 version :
Enterprise
Version 15.0 (Build 1130.7)
2 CAS servers
4 Mailbox servers
Hybrid Exchange and EOP is used for on-premise exchange
Mails get stuck in the Submission queue with error : A storage transient failure has occurred during content conversion.
Changed RemoteDomain setting 'TNFEEnabled' from $Null to $False -> NOK
Changed RemoteDomain TNFEEnabled from $False to $True -> OK, but external receipients are receiving mails with 'Winmail.dat'
Current setting TNFEEnabled = $Null