Do you know your 9-digit zip code?

Posted on June 21, 2016

Why should you know your 9 digit zip code?

The USPS is incredibly automated. It may not feel like that at times, but it is. Every mail box in the US is data point in a massive database.

From the National Postal Museum

From the National Postal Museum

Your mail box is called a DELIVERY POINT (DP) and is grouped with other similar addresses to make mail move as quickly as possible. The delivery points in a specific group are related to a geographic segment such as a city block, a large building or an especially high volume mail receiver within the 5 digit delivery area. Or as it was explained in 1963, to make your mail “zip along.”

Every piece of mail that is processed by the USPS goes through Delivery Point Validation. This validation process verifies that physical address (street, building number, directional, etc) exists in the USPS delivery database. Once this has been verified, a barcode is put on your envelope and it begins its journey to you. If your address can not be verified, the mail piece goes into a different system that attempts to figure out how to repair the address and get you your mail piece. (Note: this is only for certain classes of mail. Discounted mail has different thresholds for address review/forwarding).

Why you should know your 9-digit zipcode:

The 9-digit zipcode, when verified, includes all important components of your address. It is a good cross check to make sure YOU know the correct format of your address. This likely sounds silly, because of COURSE you know your own address. But, because there is so much address correction by the USPS it is easy to take for granted that mail can be delivered with incomplete addresses. And while it is true, the USPS does fix a LOT of address errors during delivery, having a complete address on your mail piece from the beginning will assure a minimum of delays and returned mail. If you really want to make sure your magazine, online order, or requested information gets to you quickly, knowing your address as it appears in the USPS delivery map is the best, first step.

Why you don’t really need to know your 9-digit zipcode:

In reality, regardless of zipcode format, the USPS equipment will check every address to make sure it can be verified and the results of this verification will supersede anything already on the envelope.

The PostalNerd ZipCode Fact List:

  • ZIP is an acronym for Zone Improvement Plan.
  • In 1943, the USPS introduced Postal District/Zone Numbers. These were used for large cities. They could be 2 or 3 digits. The code appeared AFTER the city name and before the state name.
  • On July 1, 1963, a more organized system was introduced using a 5 digit system. At the same time the USPS introduced the TWO letter state abbreviation. And the zip code was moved to the end of the address.
  • Deciphering the code: The first digit of the zip code designates the REGION for the mail. Zip codes beginning in 6 cover Illinois, Kansas, Missouri and Nebraska. The second two digits are the SECTIONAL CENTER FACILITY which is where the mail is going to be processed for each region. The final two digits represent the name of the town/village or, in the case of a city, the specific area within that city.
  • Robert Moon, a USPS employee, is considered the father of the ZIP code as he submitted his proposal in 1944 while working as a postal inspector. The USPS credits him with the first 3 digits of the zip code system. In 1967, the 5 digit zip code was made mandatory for 2nd and 3rd class bulk mailers. The system was soon after adopted generally for all mail.
  • In 1983 the USPS introduced the expanded Zip code called the Zip+4 or 9 Digit Zip code. As described above, this further focused the zip code to a section of specific delivery points, to allow for another level of presorting. The 4-digits refer to a grouping of delivery points either geographic (a city block, a building) or a specific destination in the case of a high volume mail recipient.
  • It is common to use -9998 for mail addressed to the postmaster, 9999 for general delivery. Zipcodes are assigned for all delivery points within the USA as well as its territories and armed forces stations.
  • There are also zip codes for independent countries of the Federated States of Micronesia, Republic of the Marshall islands and Republic of Palau, each of which is integrated into the USPS under a Compact of Free Association, an agreement dating back to 1947 when there was a trusteeship set up by the United Nations and administered by the United States Navy.
  • Mail to US diplomatic missions overseas are addressed as if were a street address in Washington DC with the 5 digit portion being a code for the city and the +4 being the USPS pouch/bag number for transit. The street name is actually a code as well. It is Pouch Number + City Name + the word PLACE to create something that looks like a street address, but is not.


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