Functionality

What is the easiest way to see if an email is failing Sniffer?

Check the Sniffer log to see if Sniffer tagged the message. In the Sniffer log, the easy way is to hunt for the queue file name.

If you have the message in a file already then you can also run it against Sniffer from the command line and check the log that is created (you will probably want to do this outside of your normal Sniffer directory.)