[x1798DE]

I've thought a lot about this and so far the solutions I've seen put forth (e.g. Flowingmail, Bitmessage, for starters) don't seem likely to get any widespread adoption, and that can be the death knell of anything like this that relies on network effects. Hell, I can't even get people to send me a PGP key even when I refuse to send them important documents without one (they just say they're going to send me one later, then forget about ever getting the document they wanted). It's really not that hard to generate a PGP key, but even motivated people don't do it.

My immediate intuitions are that 1.) this is a very hard problem to solve and 2.) if it's going to be solved in any reasonable amount of time, it needs to be bootstrapped into existing, popular methods of communication (such as e-mail). Adding some sort of PKI into the existing e-mail spec would probably be a good start, since it's just not something that people are used to dealing with.