Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds.Notice that there's nothing along the lines of "nor someone's car parked in front of the mailboxes" in there, and that's the main reason why we haven't been getting mail recently.
Our neighbors have a very steep driveway, so their visiting company parks at the foot of the driveway, in front of the mailboxes. Lazy Mr. Mailman refuses to step out of his mail truck to deliver our mail, which is kinda sucky. He'll take the time the next day, however, to write "Couldn't deliver; car blocking mailboxes" on everyone's mail.
I've asked the USPS if there's something I can do, but I'm pretty sure they're only going to tell me that we're SOL. The police also say they can't do anything about the cars. I'm sure there's some law documented somewhere highlighting that you aren't supposed to park in front of mailboxes.