If you have gone through articles about setting up and using email response then you must be having an idea that debugging email Response is a nightmare, if you don’t know where to look.
Personally what I do is to increase the log level of Inbound Communication Receiver Component to 5 and then go through the logs that are generated but it is time consuming and difficult.
While going through metalink I found this really useful article explaining the process of debugging email response in detail so, sharing the link here for everybody’s reference

