ZIP codes are a major contributor to the ability of the United States Postal
Service to employ automation in the processing of mail.
But even before ZIP Codes came into use, the United States postal department
(USPS,USPO) found ways to automate mail handling.
Automation Before Zip Codes
In 1867, the post office purchased a stamp canceling machine. It was operated
with a hand crank, and sped up the process of mail canceling.
In 1884, a belt driven version of the machine came into use, and in 1892,
the post office began experimenting with electrical machines.
More than half a century before ZIP Codes were implemented, the post office
encouraged business customers to use pre canceled stamps to speed up
the mail handling process. In 1902, the meter machine was invented by Arthur
Before ZIP codes came into use in 1963, postal service workers had to manually
read every delivery address on every single item that came into the post
office, and make a decision as to where it was going.
The Advent of ZIP Codes
With the advent
of ZIP codes, machines were able to take over much of the repetitive
sorting that humans had to do up until then. ZIP codes
and addresses can now be converted to bar codes that are readable by
Once ZIP codes came into use, postal workers only had to scan the five
digit numbers and type them into letter sorting machines. This speeded up
the process considerably.
Later, this process became even faster. The post office employed machines
with optical character recognition (OCR) software that was able to read
addresses and zip codes, so postal workers no longer had to type the
ZIP codes into the letter sorting machines. After a machine reads the
and address, it sprays a bar code onto the envelope that is the equivalent
of that ZIP code and address.
A bar code sorter machine is then able to classify this bar-coded mail.
A postal worker feeds the mail into the machine, which then reads the
bar code and sorts the mail by town or street. This sorted mail is loaded
trays, and then put onto trucks or airplanes to bring it closer to it’s
ZIP + 4 Codes & the United States Postal Service Today
ZIP codes helped to further automate and speed up the mail delivery process
when they were enhanced to become ZIP + 4 codes. These new nine digit numbers
allowed machines to even further pinpoint the final destination of each
When a letter is dropped into a mailbox, it lands in a plastic tub at the
bottom of the receptacle. A postal worker picks up the tub and transfers
the mail to a cloth bag. This bag is loaded on a truck and taken to the
closest post office that prepares mail for processing.
Workers feed the mail into an Advanced Facer-Canceler System. This is a
machine that arranges letters so that the address sides face the same way.
It cancels the mail with a wavy printed line and prints the postmark onto
each letter. The postmark shows the date, city and state where the letter
The Advanced Facer-Canceler System sorts the mail into three groups depending
on how the address has been put on the envelope: handwritten addresses,
typed addresses, and bar coded addresses. The bar coded addresses contain
the ZIP Code information used to sort the mail for delivery and usually
appear near the edge of the envelope.
Handwritten addresses are recorded by the machine and sent to the Remote
Bar Coding System. This system reads the images of the addresses and translates
them into bar codes that it sprays on the envelopes.
Letters with typed addresses are sent to a Multiline Optical Character
Reader (OCR) that similarly reads the ZIP Code and address information and
sprays a bar code onto each envelope.
If the machines can’t read the address on a letter, it is sent to
workers who try to match the address that appears on the envelope with
a real address. If they find a match, a corresponding bar code is sprayed
on the envelope. If the address can’t be read by postal workers, or
an envelope isn’t addressed at all, it is sent to a Mail Recovery
Center. There are three such centers in the United States, where workers
the mail to look for information on where it should go. If the destination
be determined by the contents, the letters are destroyed after 90 days.
The original Mail Recovery Center was called the Dead Letter Department,
established by Benjamin Franklin in the 1770’s.
Mail that is to be delivered within the city from which is was sent is
put in a section of the post office for local delivery. The rest of the
mail goes into metal boxes and is delivered by truck to either processing
centers if the delivery address is less than 200 miles away, or airports
if it is
Mail delivered by plane is usually stored in the baggage area of commercial
airlines. From the destination airport, the mail goes to a local processing
center. At the center, the mail is fed into a Delivery Bar Code System.
This machine reads the ZIP codes and addresses from the bar codes on each
letter, and sorts the mail into groups for each carrier’s route.
ZIP Codes are the backbone of the United States Postal Service automation
that we have come to rely on today.