From Wikipedia: Postal Service Act

I'm on a roll

This is the bill that took the constitutional power and turned it into a federal institution.

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William Goddard, a Patriot printer frustrated that the royal postal service was unable to reliably deliver his Pennsylvania Chronicle to its readers or deliver critical news for the paper to Goddard, laid out a plan for the "Constitutional Post" before the Continental Congress on October 5, 1774.[2] Congress waited to act on the plan until after the Battle of Lexington and Concord on April 19, 1775. Benjamin Franklin promoted Goddard's plan and was appointed as the first postmaster general under the Continental Congress beginning on July 26, 1775,[3] nearly one year before the Congress declared independence from the British Crown. Franklin's son-in-law, Richard Bache, took over the position on November 7, 1776, when Franklin became an American emissary to France.

Franklin had already made a significant contribution to the postal service in the colonies while serving as the postmaster of Philadelphia from 1737 and as joint postmaster general of the colonies from 1753 to 1774. He was dismissed as colonial postmaster general after the publication of private letters of Massachusetts Royal Governor Thomas Hutchinson in Massachusetts; Franklin admitted to acquiring the letters (probably from a third party, and not in any sort of official capacity) and sending them to Massachusetts. While postmaster, Franklin streamlined postal delivery with properly surveyed and marked routes from Maine to Florida (the origins of Route 1), instituted overnight postal travel between the critical cities of New York and Philadelphia and created a standardized rate chart based upon weight and distance.[4]

Samuel Osgood held the postmaster general's position in New York City from 1789, when the U.S. Constitution came into effect, until the government moved to Philadelphia in 1791. Timothy Pickering took over [5] and, about a year later, the Postal Service Act gave his post greater legislative legitimacy and more effective organization. Pickering continued in the position until 1795, when he briefly served as secretary of war, before becoming the third U.S. secretary of state.

Because news was considered crucial to an informed electorate, the 1792 law distributed newspapers to subscribers for 1 penny up to 100 miles and 1.5 cents over 100 miles; printers could send their newspapers to other newspaper publishers for free. Postage for letters, by contrast, cost between 6 and 25 cents depending on distance.[6] This subsidy amounted to roughly 0.2 percent of US Gross Domestic Product (GDP), according to McChesney and Nichols.[7]

The postmaster general's position was considered a plum patronage post for political allies of the president until the Postal Service was transformed into a corporation run by a board of governors in 1971 following passage of the Postal Reorganization Act.