They know the person through other channels, envoy is not the only means of communication
The person comes back and admits to others they had an account banned. Guess what you can ban an email, you can ban an IP, you can ban a payment method. But you can't ban a person except in wording. Evony can say someone is banned but the person can change there email, they can change there IP, they can use a different payment method, they can lie about there name. So it is impossible to actually prevent someone from returning, it can only be complicated and if there offence is bad enough add another ban whenever they are noticed as being backed.

So yes it is up to the players to do the bulk of the finding. Note I said bulk not all.