I dumped Proton when Yen blathered about the GOP being better for privacy... Glad I did even though it was disappointing to have to move email addresses again.
For those shopping for email providers, I use Posteo. At the time I was looking at them, AI hadn't quite been shoved everywhere yet so I didn't ask them their policy. https://posteo.de/en
I wrote support to ask what I could tell those who are considering Posteo now about what their AI policy is. This was the reply:
@ml this looked pretty good, so I signed up and paid, with the intent of migrating away from the Proton family plan.
But, I can't actually see an option to link your personal domain. I also see nothing in the documentation that suggests this is possible.
I hope I'm wrong, but if not, this is sadly not an alternative to Proton.
I don't think I'm going to ask for my money aback because it's my fault for not looking up this before I paid, and perhaps they will add this feature in the future, at which point I'll be happy to migrated to them.