Not only is conversation grouping, a major problem already (i.e. it just finds emails by subject, not by actual email header). Tuta manages to do this, even though they encrypt the header. The excuse that we can't read your email is wrong, because the client must decrypt the message so we can read it, so surely the client can thread the emails correctly.

But even worse, if you search for anything, you get pages and pages of un-threaded emails. Every incoming email, and response, in chronological order, so if you find one email that's related to the person/thread you need, the actual email you want might be mixed in with other emails you sent that day.

It's unworkable.