For me, what actually makes me not using it is because it does not support Exchange without IMAP support which my university disable. Otherwise it is the best UX/UI email client on Linux.
I do also remember the part about Exchange not being supported if IMAP is disabled. I had the same issue when I tried to use it at a university, but luckily haven't needed that since. Not surprising to hear that it hasn't changed either.
I've been using Postbox but unfortunately they got acquihired by eM Client. So much for lifetime license. Won't fall for that again.
Meanwhile, Thunderbird has resurfaced. So I might switch back to that instead.