If the majority of mail stops are junk mail only, I would love to see some napkin math of the effect of all those diesel/gasoline accelerations per mailbox, dropped across the daily fleet of drop offs.
No they don’t, that’s what the red flag on the mailbox is for. Everywhere I’ve lived, if you don’t put the flag up and there’s no incoming mail for you, they don’t stop.
Of course, where I live the USPS person stops in a general area and does all the outgoing deliveries on foot, but it's conceivable that some days an entire block may receive no incoming mail. Also, we need to take into account things like fuel costs for planes & such throughout the entire supply chain.