If a postal employee comes on your property to deliver your mail and is attacked by a dog, they can pepper spray the dog and you have no arguments.
The postal service can refuse to deliver your mail, you have to pick ut up at the PO. In some cases I have seen on TV it can escalate to no mail to anyone on your block until the post office is sure the problem has been taken care of..
the post office can then refuse to deliver your mail, they will make you get a PO box. Postman are not considered a snack...