And what do you actually use? I know the answer is probably self-hosting but maybe there are other solutions for a decent privacy.
Never use email for anything requiring privacy. Email is for paper trails. That’s it. Sometimes for you, often times against you. It doesn’t matter if you use Proton, Tutanota, FastMail, Gmail etc. The other person probably isn’t and they + their provider will share anything you send so be on your best behavior.
Certified email would solve this, if it was possible to self host it.
Unfortunately running it requires government approval and the resulting emails are legally binding, so I assume hosts will have to go through all kinds of security controls and audits.
I think that misses the point. Emails are kind of antithetical to transient and private communications. People are much better off using a generally respectful service that doesn’t scan their mail for normal use and turn to better tools like Signal (which require both receivers to use an agreed-upon/enforced and privacy-focused infrastructure) or any other messenger with disappearing chats that limits metadata retention.