What I don't understand is that pretty much everyone has an incentive to eliminate spam. ISPs to reduce traffic, emails providers to produce a better service and spend less time dealing with spam. Users for obvious reasons. Only the NSA enjoys the current unencrypted status quo. Why doesn't it happen? Why are we stuck with a 30y protocol?
And unless you permit sending a single message to both SMTP and better-than-SMTP recipients without any UI awareness, you've built a product that's strictly worse than SMTP for end users.
You could add features to email to make a more compelling product, and then kill seamless integration with other SMTP users and still have a better product. (See e.g. Slack. Or Facebook, for personal email.) And then maybe in many many years nobody will want email any more. But that won't be quick.
If Gmail, Yahoo, Microsoft, and Comcast announced that they are making it more likely that outside email (from online stores, from individual Exchange installations, etc.) will be marked as spam when it's not actually spam, people will find new email hosts. Somehow.
If they just want to mark traffic as spam when it is, they're already doing that.
Almost every business relies on OpenSSL or some equivalent, but how many actually learn enough about SSL to contribute back to the codebase? Not many, because despite the need there's little acclaim or funding to be had pursuing things that won't make direct revenues, regardless of their importance.
Protocols like this generally don't get updated until it becomes a matter of necessity -- either by public awareness (we're far from that point) or someone designing the "next big thing" needs an un-implemented feature and contributes.
Fixing smtp should be as important if not more than upgrading http 1.1.
My point though, is that it's always a "secondary" or "tertiary" business concern... a point emboldened by the number and frequency of data breaches -- always followed of course, by the email newsletter follow-up & mea culpa. "We care about the security of your data, we swear. We regret to inform you that ..."
Sadly things are not always as they should be, friend...
[edit] also a system of extended validation for signatures like for ssl certificates would be useful. I would end up expecting a nice green logo in my mail client for emails from citibank.com, something cit1bank.com could not achieve.
[edit2] also a modern design would require emails to be instantaneous. All these messenger apps would become redundant and we would revert to a common standard.
http://craphound.com/spamsolutions.txt
Good checklist of things a potential "reformed SMTP" needs to do.
If the Wright Brothers wanted to eliminate auto accidents by flying, anyone at the time could have told them they were doomed to failure, and history would have proven them right, even though air travel is safer than road travel. That's because getting people to stop using cars isn't simply a matter of inventing an airplane.
Someone should write up such a list along with a bot that replies to any post that cites the craphound link linked above. I think it's a valid counterpoint.
Nevertheless, whenever someone offers up a cure-all for SMTP, that craphound list is the first thing that comes to mind.