I think this comment deserves some nuance. Every company has to comply to local laws. Unless you want to run something illegal, at which point it's not a very reliable alternative for all your mail and more.

Proton in some cases was forced to turn over whatever they knew of a few accounts, according to Swiss law. They try to obfuscate as much as possible, so they can't turn over complete e-mail conversations. But some info is in there, and they have to turn that over. But (correct me if I'm wrong) they have to only comply to Swiss law, when there's a court order.