Carriers must know their districts, understand regulations covering the delivery of mail, handling of registry, insurance and collection on delivery matter, collection of mail and handling of change of address and forwarding orders. The inspector, however, determines when conditions are such at an office that city delivery service may be installed, the number of carriers necessary, and the number of deliveries to be made. He lays out the routes, locates the collection boxes, and fixes the schedules. He is also called on to investigate the service when extensions are desired or when carriers are deemed necessary, and is concerned with clerks, supervisory officers, postmasters, new post-offices, railway mail service, contracts for transportation of mail and furnishing of supplies, as well as the enforcement of criminal statutes covering train robberies, post-office burglaries, money-order forgeries, lottery men, the transmission of obscene literature, mail-bag thieves, embezzlers, etc.
The following regular employees were in the Post-office Department and Postal Service on July 1, 1922:
| Post-office Department proper | 1,917 | |
| Post-office inspectors | 485 | |
| Clerks at headquarters, post-office inspectors | 115 | |
| Employees at United States Envelope Agency | 10 | |
| First Assistant Postmasters: | ||
| First class | 834 | |
| Second class | 2,808 | |
| Third class | 10,407 | |
| Fourth class | 37,899 | |
| 51,948 | ||
| Assistant postmasters | 2,730 | |
| Clerks, first and second class offices | 56,003 | |
| City letter carriers | 39,480 | |
| Village carriers | 1,111 | |
| Watchmen, messengers, laborers, printers, etc., in post offices | 3,063 | |
| Substitute clerks, first and second class offices | 11,283 | |
| Substitute letter carriers | 10,765 | |
| Special delivery messengers (estimated) | 3,500 | |
| Second Assistant: | ||
| Officers in Railway Mail Service | 149 | |
| Railway postal clerks | 19,659 | |
| Substitute railway postal clerks | 2,419 | |
| Air mail employees | 345 | |
| Fourth Assistant: | ||
| Rural carriers | 44,086 | |
| Motor-vehicle employees | 3,177 | |
| Substitute motor-vehicle employees | 447 | |
| Government-operated star-route employees | 64 | |
| Total | 252,756 |
The following classes or groups are indirectly connected with the Postal Service in most instances through contractual relationship, and take the oath of office, but are not employees of the Post-office Department or the Postal Service:
| Clerks at third-class offices (estimated) | 13,000 |
| Clerks at fourth-class offices (estimated) | 37,899 |
| Mail messengers | 13,128 |
| Screen-wagon contractors | 201 |
| Carriers for offices having special supply | 349 |
| Clerks in charge of contract stations | 4,869 |
| Star-route contractors | 10,766 |
| Steamboat contractors | 273 |
| Total | 80,485 |
