If you pay Proton Mail for a service, they may hand over the payment data in response to a court order: https://www.404media.co/proton-mail-helped-fbi-unmask-anonymous-stop-cop-city-protestor/
Proton Mail Helped FBI Unmask Anonymous ‘Stop Cop City’ Protester

A court record reviewed by 404 Media shows privacy-focused email provider Proton Mail handed over payment data related to a Stop Cop City email account to the Swiss government, which handed it to the FBI.

404 Media
@evacide so the only real solution is to run your own mail server, because corporations will always do this if pressured?

@caitp @evacide I run my own mail server and spammers have made deliverability impossible for lil guys like me.

I run my own server out of Germany, but I also have to text all of my friends to check their spam folders whenever I email them 🥲🥲🥲

@waffles

It is possible to make it work even to google and hotmail but it takes dedication and constant upkeep sadly. And it does not anonymize you at all, rather the opposite.