Enter the complete address into the United States Postal Service’s Look Up a ZIP Code tool to find a ZIP+4 code. In order to find an address in normal USPS formatting, the tool also allows you to enter a ZIP+4 number in the appropriate box.
During World War II, the Post Office started utilising postal district or zone designations in major cities. To ensure that addresses with ZIP codes would continue to fit on magazine mailing labels, it established the five-digit ZIP code and the two-letter state abbreviations in 1963. For second and third class mail, the USPS started enforcing the use of acronyms and ZIP codes in 1967.
The ZIP+4 codes were introduced by the USPS in 1983. In 1983, the postal service provided discounts for senders of big volumes of mail due to early reluctance. But because of the overwhelming public opposition, the USPS does not mandate the use of the extra four digits.
There are some instances where the four digits do not always signify a unique mailbox. As of 2015, the USPS employs a digital optical scanner to read the address and imprint an 11-digit bar code that identifies a specific mail delivery point on every piece of mail. The eleven digits consist of the ZIP+4’s nine digits plus two more digits for the delivery point.