My lack of trust is the sole reason I never had email on my phone until a few months ago. I moved to ProtonMail and I use their app (which is great). I trust them. It's possible I'm wrong, but I know how they make money and if I use them long enough I'll be a paying customer when my free space runs out. They also open-sourced their codebase and I have a friend in law enforcement who has delivered warrants to them and they truly don't keep any data or have access to emails at all.