I found this site recently which is perfect for those worried that email, once sent, probably exists forever on some server somewhere. This is not an exaggeration. Read about FBI computer forensic scientists, and you can get seriously paranoid. Luckily, most of us aren't worried about divulging Great Aunt Hattie's recipe for Banana Nut Cake in an email. The only repercussions might be a little haunting from the beyond.
However, if you are worried that the life of an injudicious email is remarkably similar to a radioactive substance, then rush over to Big String where you can sign up for a free email account that will enable your emails to not only be recalled once you come to your senses, but also they can self-destruct.
Isn't that cool? Must be a book premise in there somewhere.