Do you use E-mail Center Auto-Processing functionality?  Auto-processing rules can be defined which will process an email and initiate actions such as sending an auto-reply, auto-acknowledgement or service request update or creation. 

If you're using auto-processing in your environment, then you will have noticed that, when things go wrong, often the only indication that there is an issue is if the email goes to the Supervisor Queue for manual processing instead of being sent.  Oracle Development has developed a script to help you debug when an email is meant to be auto-processed but is failing. There are scripts for R12.0.6 through to R12.1.3.

See Doc ID 1427925.1 for details of the script and how to use it.