The "/unsubscribe" page:

If a valid subscriber code is supplied in the name= query parameter, then that subscriber is delisted.

Otherwise, If the users is logged in, then they are redirected to the /alerts page where they have an unsubscribe button.

Non-logged-in users with no name= query parameter are invited to enter an email address to which will be sent the unsubscribe link that contains the correct subscriber code.