No thanks. I still recoil at the sight of a read-receipt and the only reason most companies include any of this dreck in an email in 2021 is to either track me or market to me.
make email text again.
That ship sailed the instant it got named "email" instead of something like "etelegram".
With mail, I can send anything that my printer can print, which is everything my word processor can handle (fonts, text decoration, foreground and background colors, inline images, graphs, tables, and more) and attach anything that fits in the envelope (a CD-ROM of arbitrary data in any format).
It was inevitable that email would end up being able to handle the electronic equivalent of all those things.
The problem with email is not that it now handles more than just plain text. The problem is that there was no early agreement on how to handle those things, so different implementors came up with different ways to do it, which eventually converged on using HTML. Not because HTML was necessarily the best way to do it, but because it was something they all already implemented for other things or was already available on the systems their mail clients ran on.
But modern HTML engines are designed for the web, so there still really needs to be some sort of agreement on a subset of HTML that handles the things necessary to make email like mail, without including things that make sense for the web but not for mail.
What would you think only makes sense for the web and not for mail?
That should work to each party’s satisfaction.
Just sending something registered won't help your jurisprudence :p
Likewise, if it's refused, it's on the recipient to be responsible for whatever they didn't accept
Good email clients already provide a very simple solution: a user option to disable loading remote content, with a per-message option to load it.
Your suggestion would mean that my mail client has to download a ridiculously larger volume of data than it does now.
To expand a bit: With css, you can specify a background image to any document element. Something like this, where the url serves to identify you:
div.foo {
background-image: url('https://example.com/bar.png?t=deadbeef')
}