Not really, if you take a major metropolitan area there are plenty of mailboxes. The post office also happens to have a list of these mailboxes, if you use ran

Not really, if you take a major metropolitan area there are plenty of mailboxes. The post office also happens to have a list of these mailboxes, if you use random selection and travel during peak hours they can't reduce much below the 'people who live in the metro area and commute' level.