What about the fact it’s a US-based product so you’re under forced Five Eyes data collection?
And how does Protonmail help when Switzerland has signed the Mutual Legal Assistance Treaty with the US? If they need anything, they’ll get it.
Fastmail is not a US product, it is Australian. Australia is part of 5 Eyes though.
Almost every email is going to or coming from US servers anyway. Better to treat email as insecure and use something else for more secure communication.