That fortune article you linked to is a farce written by someone trying to push a agenda of doing away with the post office.
https://fortune.com/2015/03/27/us-postal-service/
"He estimates that, all told, the subsidies and legal monopolies that Congress bestows upon the post office is worth $18 billion annually."
What the heck is this guying talking about?
The post office has a SINGLE monopoly on First Class Mail under the U.S. Constitution. The post office was established by the Second Continental Congress in 1775 and predates the the ratification of the Constitution in 1788.
"Post office officials have often attributed the losses to the decline in demand for first class mail in favor of more efficient modes of communication"
Here are the actual facts:
https://facts.usps.com/table-facts/
First Class Mail volume has dropped from 77.6 billions pieces in 2010 to 16.5 billion pieces in 2019. That is due to more efficient ways of communication such emails, online bill payments and online banking which do not require the use of First Class Mail services.
"and congressional mandates"
Below is a link to an article from February, 2020, regarding a vote in House of Representatives to end the horrible Postal Accountability and Enhancement Act which required the prefunding of retirement costs for 75 years. This bill required USPS to set aside up to $110 billion dollars over the course of 10 years to cover the potential cost of retirees for the next 75 years.
USPS had lost money for 13 years straight and most of those loses have been due to this bill. In 2019; for instance, 83% of USPS's $8.8 billion loss was due to this bill that was introduced by Congress to raid USPS funds to offset their own overspending. This money is not sitting in an account anywhere earning interest for USPS. Congress has already spent it and given USPS a IOU just as Congress has given the American taxpayers an IOU for all the money paid into social security all these years.
govexec.com/pay-benefits/2020/02/house-votes-end-controversial-usps-payments-future-retirees-health-care/162912/
"Saturdays and to unprofitable parts of the country"
Actually its far worse than that. Congress has has along history of requiring more and more from USPS beyond it original mandate. The oldest form of Congressional fraud in regards to the Post Office was appointing unqualified family members, friends and political allies to local postmaster jobs.
When the Post Office was established by the Constitution its distance based fees only covered the transfer of items from one post office to another post office. It didn't include home delivery. It was your job to get your letter to a local post office. Whoever was to receive the letter needed to get to travel to the local post office to pickup it up.
Free delivery to a limited number of city addresses was not introduced until 1863 when local revenues would cover expenses. By 1880 it was offered in 104 cities and 796 cities by 1900. Free rural delivery was not experimented with until 1896 and did not become permanent until 1902. Parcel Post was added in 1913.
Saturday delivery has been suspended in 1947 for some cities due to budget problems. In 1957 it was temporarily suspended nationwide. Parcel Post Saturday delivery was suspended in over 6,000 cities from May 1964 to January 1966 due to budget concerns.
about.usps.com/who-we-are/postal-history/delivery-monday-through-saturday.pdf
"Laws that bar any other shipping service from delivering mail and packages directly to residential and business mailboxes."
What is this guy talking about?
USPS has a monopoly on First Class Mail which includes letters and small packages that weigh up 13 ounces (15.9 ounces commercial rate). UPS and FedEx are free to delivery packages to residential addresses so long as they do not contain First Class Mail!
"The Post Office is exempt from state and local property and real estate taxes, along with other burdens like tolls, vehicle registration fees, and parking tickets. These exemptions save the USPS $2.18 billion per year."
But then UPS & FedEx both USPS to complete deliveries as it cheaper than completing the delivery themselves. So how much does this save FedEx and UPS?
In turn USPS's largest paid contractor is FedEx, which uses it fleet of airplanes to move USPS's time sensitive packages, with USPS completing the final delivery. So how much less business would FedEx have if USPS dropped them as a contractor?
"These higher labor costs, plus the absence of a need to innovate due to government-granted monopolies"
Once again what is this guy talking about? USPS has a monopoly on First Class Mail only.
