Hard for me to understand how blocking valid email providers like Proton, Tutanota, and Skiff, would actually mitigate any abuse. All it’s going to do is hurt the websites with this filter and prevent privacy-minded folks from signing up. Unfortunate to see, hopefully they get some common sense and don’t block these for no reason.
Not sure how it hasn’t been said yet, but I really like Helium314’s OpenBoard fork. Can’t recommend enough.