They want your IP or your phone. Use a VPN IP or TOR and they’ll require a phone number. That’s been my experience at least. I don’t trust them.

100%, like you said, email isn’t really made for private communications. Even with me calling it out as not private, I do use fastmail as my main provider and like it.

It’s great except it’s hosted in Australia. Not really privacy focused.

Usually it’s OpenWRT