39 CFR § 241.2 - Stations and branches.
(1) Stations are established within the corporate limits or boundary, and branches are established outside the corporate limits or boundary of the city, town, or village in which the main post office is located. Stations and branches may be designated by number, letter or name. As a general rule, branches are named.
(2) Stations and branches transact registry and money order business, sell postage supplies, and accept matter for mailing. Delivery service, post office boxes, and other services may be provided when directed by the postmaster.
(3) Stations and branches, except nonpersonnel rural stations and branches, are designated as independent when registered and other mail is received or dispatched without passing through the main office.
(b) Classification -
(1) Classified. Operated by postal employees in quarters provided by the Federal Government.
(2) Contract. Operated under contract by persons who are not Federal Government employees. Persons operating contract stations and branches are independent contractors and neither the contractors nor any person employed by them to assist in the conduct of contract stations or branches shall be employees of the Federal Government for any purpose whatsoever.