> Yup, xmpp checks all of those boxes too.
Well, except one.
Go find a random nontechnical person and tell them "send me an xmpp" and see if you ever get that message!
Email not only has all the technical advantages noted above, but also the advantage of universality. Just about everyone who has ever used the internet, no matter how nontechnical, will have sent emails so they'll know how to reach you.
