Looks like the U.S. Postal Service isn’t taking any more attitude from your dog.
Update - Jonah, in the comments: "I would advise the postal service to have their ammo delivered by FedEx to avoid it being delivered to their neighbor's mailbox."
"There are countless horrible things happening all over the world and horrible people prospering, but we must never allow them to disturb our equanimity or deflect us from our sacred duty to sabotage and annoy them whenever possible." -Auberon Waugh