This major group includes all establishments of the United States Postal Service. Post Office contract stations are classified in Services, Industry 7389. Establishments primarily transporting mail on a contract basis for the Unites States Postal Service are classified in Industry Group 421 and Major Group 45. Private postal services primarily engaged in the delivery of unaddressed advertising materials are classified in Services, Industry 7319, and private establishments delivering individually addressed letters, parcels, and packages are classified in Industry Group 421 and Major Group 45.