Hmm.... LazyTruth is "an inbox widget that surfaces vetted information when you receive an email forward full of political myths, urban rumors, or security threats."
I don't know how complicated their analysis is but this would be a fascinating machine learning problem if you wanted to really follow it through. I'm not sure who would use it though. It actually sounds like something you'd want to set up on other people's email clients to shield them from lots of misleading information. But that would kind of disrespectful of their ability to come to their own conclusions wouldn't it?
What could be useful would be if your email tool read incoming emails from certain addresses and attached relevant lists of weblinks to vet their content so you'd have information at your finger tips if you wanted to create a related blog post or share with your own network. Wordpress already has suggested links for related articles that show up while you write a blog post, this would be simply pushing that one step further to your inbox to allow you to grab links in your email rebuttals...if anyone does email rebuttals.
Sort of sounds like one of those cases of something that is possible looking for a reason to be done.