> Let's design the successor to email on top of HTTP
You can stop there, I've heard enough. Not everything is hypertext.
From the first paragraph:
>The goal is not to replace the current mail system, heaven forbid!, but to learn, have fun and discover current technologies to swap out every element: sending, receiving, gateway, keys, and so on.
It's all for fun.
Usually, informed people only read the headline.
And HTTP transports many, many more things than hypertext. It seems like a sensible choice for this use case in terms of capabilities.