> I’m asking if there’s any feasible way for ProtonMail to not have the ability to know which IP addresses connect to their services.

Maybe ProtonMail could offer an alternative .onion service? This way they couldn't legally be forced to give a way the IPs, because on the other end it's a TOR exit node anyways. And by design they cannot see the real IP from their point of view, so a legal enforcement would be useless.

That’s a good point - mandating Tor usage. The Guardian also provides a Filedrop Onion service.

Though I guess you could also access via Tor regardless, if not for the account creation stage.