Editing ZIP Code (section)

===ZIP+4===
In 1983, the U.S. Postal Service introduced an expanded ZIP Code system that it named ''ZIP+4'', often known as "plus-four codes", "add-on codes", or "add-ons". A ZIP+4 Code uses the basic five-digit code plus four additional digits to identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail, a post office box, or any other unit that could use an extra identifier to aid in efficient mail sorting and delivery. However, the new format was not adopted universally by the public.<ref>{{cite web|url=http://www.randomhistory.com/zip-code-history.html|title=Organizing America: A History of the ZIP Code|date=25 July 2014|website=RandomHistory.com|publisher=Random History|url-status=dead|archive-url=https://web.archive.org/web/20140812203838/http://www.randomhistory.com/zip-code-history.html|archive-date=12 August 2014|access-date=19 June 2017}}</ref>

Commercial customers generally apply a ZIP+4 or a delivery point code (i.e., ZIP+6) to mail as part of address normalization. They may need to do so to receive discounted postage rates.<ref>{{Cite journal |date=11 July 2013 |title=New Standards to Enhance Package Visibility |url=https://www.govinfo.gov/content/pkg/FR-2013-07-11/pdf/2013-16524.pdf |journal=[[Federal Register]] |volume=78 |issue=133 |pages=41721-41731}}</ref> The public does not need to write the ZIP+4 code, as mail is read by a [[Multiline Optical Character Reader|multiline optical character reader]] (MLOCR) that almost instantly determines the correct ZIP+4 Code from the address—along with the even more specific [[delivery point]]—and sprays an [[Intelligent Mail barcode]] (IMb) on the face of the mail piece that corresponds to 11 digits—nine for the ZIP+4 Code and two for the delivery point.

For [[post office box]]es, the general but not invariable rule is that each box has its own ZIP+4 Code. The add-on code is often one of the following: the last four digits of the box number (e.g. PO Box 107050, Albany, NY 12201-7050), zero plus the last three digits of the box number (e.g., PO Box 17727, Eagle River, AK 99577-0727), or, if the box number consists of fewer than four digits, enough zeros are attached to the front of the box number to produce a four-digit number (e.g., PO Box 77, Juneau, AK 99750-0077). However, there is no uniform rule, so the ZIP+4 Code must be looked up individually for each box (e.g. using the USPS's official ZIP Code Lookup tool, and being sure to enter just city and state, not the 5-digit ZIP).<ref>{{cite web |url=https://tools.usps.com/go/ZipLookupAction_input |title=ZIP Code™ Lookup {{!}} USPS |website=tools.usps.com |access-date=2020-01-23 |archive-date=December 22, 2016 |archive-url=https://web.archive.org/web/20161222044440/https://tools.usps.com/go/ZipLookupAction_input |url-status=live }}</ref>