The U.S. Postal Service employed 75,000 clerks; 335,000 mail carriers; and 209,000 mail sorters, processors, and processing machine operators in 2004. Most of them worked full time. Most postal clerks provided window service at post office branches. Many mail sorters, processors, and processing machine operators sorted mail at major metropolitan post offices; others worked at mail processing centers. The majority of mail carriers worked in cities and suburbs, while the rest worked in rural areas.
Postal Service workers are classified as casual, part-time flexible, part-time regular, or full time. Casuals are hired for 90 days at a time to help process and deliver mail during peak mailing or vacation periods. Part-time flexible workers do not have a regular work schedule or weekly guarantee of hours but are called as the need arises. Part-time regulars have a set work schedule of fewer than 40 hours per week, often replacing regular full-time workers on their scheduled day off. Full-time postal employees work a 40-hour week over a 5-day period.