Whether or not the data part of email is a suitable form of communication aside, can we not just nuke the whole implementation of mail transport? Every MTA/SMTP project is a cluttered mess (quite specifically sendmail, woof), and the specs they're based on are even more convoluted. If it's not coded so shoddily it could be pushed over with a brisk swat (again, sendmail), it's overcomplicated and difficult to work on/with—and probably not because the project maintainers want it to be.
I don't see it being that difficult to create a specification based entirely around SSL/TLS with much simpler operating parameters that can still funnel mail through, since MIME is flexible.
The difficult part would of course be getting people to adopt it. I bet some people even still use desktop Outlook, the barbarians.
And now, to make a quick getaway before all the devout followers of sendmail come to raise me on a stake... If there are any left.