This was my last freelance story before moving to Winston-Salem. Basically, the U.S. Postal Service has all these longstanding relationships with local postmasters, who make extra money by renting space to the post office, particularly in rural areas.
The USPS also contracts with former, and in some cases current, employees to handle rural mail delivery routes. It's not clear whether any of this is really costing the post office which has major financial problems, more money. In some cases it seems to save money, because the rent hasn't gone up that much in 40 years.
The Post Office Inspector General's Office breaks much of this down in a report you can download here. Auditors determined federal and postal regulations were violated. They also questioned the wisdom of renting from and contracting with employees, particularly since, in some cases, postmasters helped make the decision to rent their own building.
Also, the names of the contractors are being kept secret for reasons that don't sound like good reasons to me.
At any rate, read the story. I also have databases of the leases and contracts that weren't included in the Inspector General's report. If you want them, let me know and I'll email them, save you a FOIA request.