39 U.S.C. § 1008: Temporary employees or carriers

(a) A person temporarily employed to deliver mail is deemed an employee of the Postal Service and is subject to the provisions of chapter 83 of title 18 to the same extent as other employees of the Postal Service. (b) Any person, when engaged in carrying mail under contract with the Postal Service, or employed by the Postal Service, is deemed a carrier or person entrusted with the mail and having custody thereof, within the meaning of sections 1701, 1708, and 2114 of title 18.