Introduced by the US Postal Service in 1991, the delivery point barcode ensures that mail is sorted at the recipient's post office in trays according to the walk sequence of the carrier route. As a result, carriers no longer had to case mail. An envelope's address is first scanned by a multiline optical character reader (MLOCR), which then sprays a barcode on the envelope. This barcode represents the nine-digit zip code and the last two digits of the street address.
If the MLOCR is unable to discern an address, it will spray an identifying code on the envelope. A remote operator then reviews the address via video screen and keys in a code that enables the determination of the zip code. A barcode sorter receives this information and sprays the correct 11-digit delivery point code on the envelope.
All automated mailings require the 11-digit delivery point barcode. Business Reply Mail and non-automated mail can use the standard POSTNET barcode, which represents only the zip code.