It shouldn't BE backwards compatible. That's the Microsoft problem. They can't innovate because they have 40 years of legacy holding them back. Email might be the only situation that's worse. I don't want another new layer over the top like DMARC, and I don't want to try to "fix it." It can't be fixed, it's just a bad design.

I want something fundamentally new that doesn't stink of 70's era pre-security thinking.

A group of heavy hitters needs to just form a working group and propose Email 2.0. As long as it's supported by the biggest vendors and companies and they don't go all "IPv6: It's better because it's complicated!" on it people will sign up because it will be able to offer MUCH more in terms of features, usability, security, ease of hosting, etc.