Nobody does, sadly.
Baking it into the protocol like Signal and WhatsApp did means nobody has to want it, they just get it included without having to bolt on any extras.
TYL: https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail and https://en.wikipedia.org/wiki/Pretty_Good_Privacy
I'd actually argue that email is one of the better systems, as I can manage and control my whitelist/blacklist myself. It makes things much more functional that way.
https://techcrunch.com/2016/03/24/email-is-dying-among-mobil...
And there's good reason for that. Email is basically the electronic equivalent of postal mail, a first pass at digital communication that aped the old medium. But the first email RFC was 35 years ago. MIME is more than 20 years old, and that's the last major capability improvement.
From the point of view of a teen who grew up on Facebook Messenger, Snapchat, Instagram, and Twitter, email is weird, old, and feature-deficient. They think of email in the way that I think of paper mail (mainly for formal and commercial use, not really for friends, somewhat quaint), or possibly how I think of a fax machine (quirky, obsolete, use only when forced).
We have been chatting since we have had networks. Believe me, e-mail is here to stay.
ducks