Post offices come in two flavors: Classified, which refers to offices that are operated by post office personnel; and contract -- operated by contractors paid a fixed or percentage-of-revenue amount by USPS. Such are called CPUs -- Contract Postal Units.
Contract offices are convenient for locations that couldn't support the full-time salary and infrastructure cost of a full post office (like Broad Channel, Queens, NY); or as a supplemental location to a busy post office for the sale of stamps and the mailing of packages with basic services (such as in Flatbush, Brooklyn, NY, which effectively features two post office locations within 250 feet, and another two blocks down the road). Newer and rapidly growing cities frequently feature more contract units than actual post offices, since it costs less to operate one than to build and open a new classified office (see St. Augustine, FL, among dozens of cities in Florida). Still more have operated in the community for decades, and continue as the sole operations in a given community (as in Center Tuftonboro, NH, which operates in the general store which has been around since 1822).
The latter are a special type of CPU, known as a CPO (Community Post Office); before 1971, they were known as rural branches / stations. Such have been featured in previous posts on this blog -- namely An Actually Colorful Post Office [Hawi, Hawai'i] and Big Island, Small Office [Ninole, Hawai'i].
Generally speaking, there's a clear distinction between the two varieties of offices. However, I have come across a few post offices which have "switched flavors" while remaining in the same location. Like neutrinos, I suppose.
In this instance, the Post Office took over a contract operation, and now runs it with USPS personnel. Sometimes such a transition occurs due to fraudulent bookkeeping or other violations on the part of the contractor (though in this instance, I don't know the cause). Honolulu, Hawai'i's Uptown Station had a creative approach to saving material during the change:
The Bronx, New York's Bathgate Station was originally a classified post office and is close to the Tremont Station. Perhaps too close. Instead of closing the office, the facility is run as a service to the community under contract, and the contractors provide a few additional business services:
The Franklin, Tennessee Five Points Station looks and feels like a real post office, because it is one. Well, was one. See for yourself [in this Wikipedia photo]:
This facility, which dates to 1926, earned itself a spot on the 11 Most Endangered Historic Places 1991, by the National Trust for Historic Preservation. As the town had expanded, the post office needed more space to operate. It built a new facility on the outskirts of the town, but contracted out the downtown post office operations to keep the building functional. Other local cultural operations now make their home there.
[Here's the new Franklin, TN Main Post Office facility:]