Well none of this is happening unless we are using a new mail protocol, and if we are using a new protocol we might as well throw in the kitchen sink and give

Well none of this is happening unless we are using a new mail protocol, and if we are using a new protocol we might as well throw in the kitchen sink and give you a new mail transfer agent and mail client application as well. And in the new application: Address == Public Key, Address book == web of trust. Your mail agent probably doesn't even bother to check or propagate incoming message notifications from addresses you haven't manually added to your address book (100% trust), or addresses within a certain number of hops from someone you manually added to your address book (friends of friend, boss's employees, etc.). And the mail client could further hide and ignore all of the notifications from below a certain user customizable trust score as well.