I get that you're just trying to get your software out there, but your modern features that email doesn't support are just wrong.
>shared history
Not if you have a mailing list, and then going off the record is as easy as removing the mailing list from the CC field.
>markdown formatting
This is an implementation failure, not really a fundamental problem with email. There is no reason that email clients don't support markdown, except that nobody has ever wanted it. There was someone who made a utility to switch markdown to regular MIME email, but just as a proof of concept. It works.
>Image previews
I assume what you mean by this is an inline thumbnail that expands when you click on it? Again, there's nothing about email that prevents it, it's just the way email clients are. That could be fixed
>emoji reactions
Okay, that's fair, there's no way to do this in email, short of sending a single emoji back. On the other hand, I think everyone would agree that this is more of a nice to have feature, than a necessary one, and one that really only makes sense in the world of quick, back and forth chat programs.
[1] https://begriffs.com/posts/2020-07-16-generating-mime-email....