Openmailbox would be lovely, but I had the same experience of extreme slowness. Even their web client is slow—which, fine, I'll use Thunderbird, but I could not

Openmailbox would be lovely, but I had the same experience of extreme slowness. Even their web client is slow—which, fine, I'll use Thunderbird, but I could not get POP or SMTP to work. (I currently use Protonmail.)