I've cancelled my subscription yesterday, conveniently it was about to renew at the end of the week, so I have a few days to migrate from Proton, here's what I'm thinking of, but I'd love to hear what other people are switching to
Posteo would have been my first choice actually but unfortunately they do not seem to support custom domains, otherwise I would switch to them instead of mailbox, on paper it sounds like they have more features for cheaper