This 1991 clip shows US postal workers in California processing mail. 

Begins with wide shots of the postal facility's interiors. Orange overhead lights illuminate the work areas. Looks like the facility is as big as a football field. 

We then see a row of postal workers at their work stations. Letters are organized in a tray at each station; each letter is mechanically grabbed and put onto a conveyor belt-like system. These letters eventually pass the worker at that station; the worker inspects each letter and types information into the system at his or her station. These inspected letters are then pushed down a chute, perhaps for further processing. 

All the postal workers look focused and busy, if not bored and indifferent to their work.