Simple Exploit Allows Attackers to Modify Email Content — Even After It's Sent!

That's why I send every email digitally signed with a note at the bottom that reads "If this email is not digitally signed assume that it's not from me." if the email gets changed at all my digital signature is not long valid because it hashed the original email.

Oh joy. Just passed it on to our security guys here, as well as all the engineers.