William Baude (University of Chicago – Law School) has posted Rethinking the Postal Delivery Power on SSRN. Here is the abstract:
It is black-letter law that the United States Postal Service has the power to deliver the mail–a power that is derived from the enumerated power to establish post offices and postal roads.
From the Founding until the Civil War, the federal government was thought to have a postal delivery power only within the District of Columbia and the territories — but not within states. The antebellum postal system included a network of post offices and transportation links between those offices, but it did not include home delivery of the mail, which was not implemented on a national basis until the early 1870s. Politicians and judges repeatedly denied the existence of a federal power to enter private property to deliver the mail. During this period, such a power was seen as a "great power" — one that was too important to be left to implication. The postal delivery power creates a power to trespass on private property–and such a power would not have been viewed as incidental during the founding era.
Even under the modern understanding of the necessary and proper clause, the case for a federal postal delivery power is shaky at best. If the Constitution had explicitly conferred a postal delivery power, the inference an implied power to establish post offices and postal roads would be clear, but the reverse inference does not follow. Post offices can exist without home delivery–as the experience in the early republic clearly demonstrates. Contemporary experience confirms this point: a system of federal post offices could easily be combined with private delivery by firms like UPS or FedEx.
Highly recommended.