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What is a ZIP code plus 4?

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Quick Answer

A ZIP+4 code is a nine-digit number the United States Postal Service uses to route mail to recipients. In addition to the five-digit ZIP code, it contains a four-digit identifier to further narrow down the destination of each piece of mail.

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What is a ZIP code plus 4?
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Full Answer

The ZIP code was originally developed to help the postal service route mail more efficiently, but as population density increased, the system began to show strain. ZIP+4 was instituted in 1983 to establish a more complete mail routing system. The ZIP+4 codes can, in some cases, direct a piece of mail all the way to its intended recipient, even identifying the destination floor of a building or department of a company.

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