How did POSTNET barcodes help automate mail sorting?

POSTNET (Postal Numeric Encoding Technique) barcodes were instrumental in automating mail processing by providing a machine-readable format that high-speed sorting equipment could easily scan and interpret.12

By representing ZIP codes and ZIP+4 codes as a series of bars, these barcodes allowed automated systems to quickly identify the destination of a piece of mail. When mail was processed, optical character readers (OCR) would scan the address, verify the postal code, and imprint the letter with the corresponding POSTNET routing code. This enabled subsequent sorting machines to route mail with high efficiency down to specific carrier routes, building blocks, or even individual floors within a business. This integration of coding and automated scanning was a critical strategy for the postal system to manage increasing mail volumes while controlling operational costs.12