About POSTNET Barcodes
POSTNET (Postal Numeric Encoding Technique) is a legacy 1D postal barcode symbology that was used by the United States Postal Service (USPS) to automate mail sorting. Developed in the 1980s, POSTNET encoded ZIP codes, ZIP+4 codes, and delivery point codes to speed up mail routing. It has been officially replaced by the Intelligent Mail Barcode (IMb) but remains supported in archival sorting.
How POSTNET Encoding Works
POSTNET is a numeric-only barcode representing digits using groups of five vertical bars. It is a 2-state barcode, meaning each bar is either a tall bar or a short bar (tracker). Out of the five bars for each digit, exactly two are tall bars. A POSTNET barcode begins and ends with a tall frame bar and includes a check digit calculated modulo-10 to prevent delivery errors.
Common Applications and Industries
Historically, POSTNET was printed on the bottom-right corner of business envelopes, postcards, and bills. USPS sorting machines scanned POSTNET to route letters to specific postal districts, neighborhoods, and individual street addresses. Today, while standard mailings must use the modern IMb, POSTNET is still studied in logistical history and used in legacy database archives.
Advantages & Limitations
POSTNET was highly effective for fast, automated sorting in the early days of postal automation, featuring a simple structure that could be printed by standard matrix printers. The disadvantage is its lack of tracking or mailer identification capabilities, which led to its obsolescence in favor of the more comprehensive Intelligent Mail Barcode.