Earlier quoted context omitted.
I agree in that, for me, e-mail is almost solely used for business communications and newsletters. However, I don't know of a "timeless", or otherwise decentralized, communication technology so ubiquitous that can be secured like e-mail. Signal seems to be the hip thing, but it's centralized. "Blockchain" communications, perhaps?
That is something I doubt I'll ever sign up for is my email on a blockchain lol unless it's just a hash of the email text or something for "proof" of it's origin/association.
Hopefully this system would provide a useful signal even if it was only adopted by a few big mail providers, and they could pressure newly-registered mail domains to adopt it or face delivery delays. Long-established mail domains would be grandfathered in, so most providers wouldn't have to change anything.