Hello Ian!
Thanks for your review. The application works as designed at this point. Here is the according quote from the File Navigator User Guide, Chapter 4.10:
"You can only view those EML files when you open through the File Navigator plug-in."
At the moment this is the only supported way. I'm working on a solution to add your needed functionality, which is already tracked through this feature request.
http://www.openntf.org/projects/pmt.nsf/894fe3a057d40c2885256bae003d7dd6/b389abc1cc889f4c862576a1003526e7!OpenDocument
Besides the plug-in there will be some operating system modifications necessary for telling the os which program to use when double-clicking on an EML file. At the moment I'm investigating how to do this on the different os'es (WinXP, Win Vista, Win 7, Mac, Ubuntu, ….). That's the hardest one at the moment.
But whatch for the future releases. It'll be implemented!
– RenĂ©