I wonder if we can’t build a far simpler postoffice app on http (self hosted domain space) and have a whitelisted encrypted exchange.
SMTP is text based and we’ll defined, so I would also argue that the transport being “simpler” is nonsense.
Nothing is easy about email! Having worked for years just to get reliable in and outboxes is definitely not trivial. Also SMTP is a system out of your control if you want anything verified and actually delivered.
Say you enter a form at a company,and in the message box you just leave that code so they can mail you.
And in practice some minimal address obfuscation has been enough to block any address harvesters, and setting up a contact form or something comparable (and I guess especially also subsequently keeping it spam-free!) would have been much more of a hassle.