Ever since the days of the pony express, mail delivery has been getting faster and faster. In those days, people were amazed that they could send a letter clear across the country and it would arrive in a matter of weeks rather than a few months. Today, if a letter is mailed early enough in the day, it can sometimes arrive on the same day it was sent.

Part of the reason for this speed of delivery is the five-digit zip code that we all put at the bottom of the address line. This number helps with the sorting of the mail so it can be sent out quickly. Ask anyone you meet, even small children, and they know their five digit zip code. But many may still wonder "what is the zip code +4?", which are those four digits that are now a new part of addressing our mail. But first, we need to understand what the initial five digits are for.

The First Five Digits:

The five digit zip code was implemented in the early part of the 1960s. We often think of the mail zipping through the delivery channels with lightning speed, but the word "ZIP" is actually an acronym for the Zone Improvement Plan established in 1963. Every address in the country was assigned a code. The first digit represented a specific geographical location. Any zip code with a one for example, pointed to the states of New York, Pennsylvania, and Delaware. The following two digits were assigned to specific regions in that area and the last two digits pointed to a smaller delivery zone within that region.

What Is The Zip Code +4?

That old system worked for more than twenty years but as the nation grew there needed to be an adjustment to the mail delivery system. This is where the zip code +4 comes in. The new expanded zip code tacked on an extra two digits to identify a specific area or group of apartments or offices and the last two digits designated a delivery segment like at floor in a building, the side of the street, or a specific department in a corporation. This would help them to be able to sort and deliver mail quickly. It turned out to be especially useful in high-volume areas where mailed needed to be delivered.

Think back to the 1960s when high-rise office buildings were few and far between. Now, nearly every city has hundreds of these buildings holding thousands of offices looking for mail delivery every day. Sorting that much mail can be a complicated task.

Today, however, mail can be sorted and directed and on its way to its destination in a matter of seconds. Yes, it's true we now live in the digital age but we are a long way from going fully digital. We still like to receive paper mail delivered in our mailboxes every day and with the new and improved +4 system, we can be sure it will get to us quickly. So the next time someone asks you "what is the zip code +4?" you will be able to explain it in a way that they will appreciate.