Creating HTML emails is a bit of an art form, although as anyone who's had the joy of creating an HTML email knows, it's a rather semantically ugly form of art.
Making an email work across the multitude of different devices and email clients requires an awful lot of tricks and hacks and whenever I receive an HTML email that's been built by someone else I always wonder how they did it and am curious to see if they know a better way of doing something than I do. However if you've ever tried to view the source code of an email received in gmail, you'll know it's far from clear.
So I've developed a neat little webservice. If you forward your email to debugemail(at)18aproductions.co.uk the service will decode the email for you and send you the source code. Give it a try :)
This is only a really quick beta service at the moment, more of a proof of concept, but I hope it might prove useful to someone trying to reverse engineer someone elses email.
Update - Since writing this I've also discovered that you can follow these instructions to view the source of an email in gmail (Oh well it's still a cool service!) :)