I don't know how it's actually done, but we use Kount and have a lot of different rules set up within it. I know protonmail accounts get crazy high danger ratings based on our settings.

They've got all kinds of levers within the platform based on your risk tolerance.

Being that we're talking about blocking emails based on fraud, I'd be understandable towards not wanting to share exactly on how you do it.

Yeah, that wasn't the original question. I'm a paying protonmail customer, for privacy, for my whole family. Trying to get a read of how much that's likely to be an issue in future.

They wouldn't have access to that information. ProtonMail doesn't provide it.