[akrymski]

Email is a collection of protocols stacked on top of each other, so when we're talking about replacing email you have to be specific about which part you'd like replaced. DNS? SMTP layer? IMAP layer? application / email client layer? spam filtering layer?

What you're suggesting is indeed something that can be,and will be, added to email. But there's nothing wrong in email at a lower level (SMTP say) thats preventing someone from setting this up. One thing that definitely sucks is IMAP though, would love to see that replaced by a restful protocol. But we have no alternative to a ubiquitous distributed and open messaging system that is SMTP.