The post office has been partially privatized for a long time and Congress has interfered with its operation during its entire history.
One of the largest cash cows for legislators, governors, and similar officials in the “good old days” was accepting political contributions (i.e., bribes) in in exchange for appointing people to local postmaster positions regardless of their qualifications.
Originally letters were only transported from post office to post office. That meant anyone sending you a letter had to address it in care of a post office that was the most convenient location for you to pick it up. If you lived directly on a post office to post route you could sometimes give the carrier a little extra money (i.e., bribe) to stop at your home, although this could end up getting the carrier fired.
Home delivery was not authorized until 1863 and it was limited to towns with a population of over 10,000 and with $10,000 in gross revenue in order to financially support the effort. There were only 65 cities with home delivery in 1864.
The post office experimented with free rural delivery as early as 1896, but it did become common until 1902. This was a boom to mail orders companies like Sears. These new requirements; however, forced more expenses on the post office, causing a $17 million debt by 1909. From 1863 to 1940 it operated in the red all but 8 years.
Railroads transported mail for over 100 years. I got to talk to some old timers back in the late 1970s and early 1980s who worked for the local post office back got five mail trains a day.
Airmail was handled by many private contractors. Passenger airliners were also used to transport mail.
USPS used many different contractors to move mail over the world’s oceans via surface mail. I had some pen pals back in the 1970s and 1980s and it would take weeks for a letter to reach them via surface mail.
FedEx is USPS’s largest air contractor. Dejoy has wanted to move this to back to surface transportation as hiring FedEx greatly increased costs.
USPS uses many ground contractors, including such large companies as J.B. Hunt.
We had a local gentlemen who worked as a post office contractor for multiple decades. He used his own straight truck to pick up mail and packages from various post offices on a route and deliver them to a large regional post office that served as a central distribution site to a post office sorting center about 80 miles away.
There are over 2,700 contract postal stations operating in various locations such as grocery stores. Back in the 1990s a local town of just 150 people had a post office operating out a portion of the postmaster’s house.
The post office hires various other contractors to do work. The local post office has a janitor come in to clean it who is not a postal employee. I was even the local post office’s snow removal contractor for 20 years, starting in junior high school.