Some weeks ago, I’ve come across Delta Chat, whose main thing is “(near) instant messaging using your email”
That left me thinking, has this been attempted before? If not, why? Also, why (besides servers’ limitations as means to fight spam) isn’t this solution used more often, given that e-mail has been a decentralized solution for well over 40 years now?
Plus there’s the issue of overhead. An email might be simple, but look at the raw message and there’s a lot of stuff being sent for each email.
So this is true (and increasingly so recently), but a lot of that overhead is technically unnecessary for the message to be sent and received; a lot of it is information about transmission and DKIM validation, spam protection, sender verification, etc; and then a TON of it is HTML for display. For a known receiver to send a message to a known recipient, I believe that a text-only email that’s cryptographically signed for identity validation could potentially be a tiny fraction of the size of a big huge HTML email.