Thanks for the info. The link seems to be the standard mail.app link and words across Mac, iPad and iPhone. Things 3 is doing something on their end to capture the link once you forward it to you inbox. There are no scripts required. I will check out your script however.
I saw that the Mac App Things 3 has a feature where when you forward an email into their inbox that todo includes a link back to the email in Mac Mail.app as well as when you do it from Mail in iOS. Can Mail to Evernote add that funcitionality?