yeah that’s missing, but also not the easiest thing for us to add, because for example for gmail we need to convince them to allow us with videos, were we don’t know if even a human reviews the thing, its just annoying to write with google robots, it took us months to make gmail work, not just the technical part, just alone the bureaucracy with gmail.
What provider do you want to see in particular? Proton mail won’t work that easily because proton mail does not use IMAP (and their proxy needs a paid account and is untested with deltachat).