This removes the need for the sender to authenticate, so it allows the service to be dumber and not register anything if it doesn't want to. However the sender

This removes the need for the sender to authenticate, so it allows the service to be dumber and not register anything if it doesn't want to. However the sender still connects to the service with a message for someone, so the service can still make the link if it wants. How much is anonymity of sender protected here?