Kid Asked

How does mail get to your house?

Tap the yellow button to begin.

For the grown-up

The short answer. Step by step. The address says where it goes and the stamp pays for the trip. A mail carrier picks it up, and at a big sorting building a machine reads the address and prints a barcode on it. Trucks, or planes for long trips, carry it near you. There a machine puts it in the order of the houses on your street, and your carrier brings it.

These pages follow one letter from a friend's mailbox to yours. Here is what really happens at each step in the United States, a few numbers, where the pictures stop being true, what to ask, and how to see it for yourselves on your own mail.

How a letter gets to you

  1. The address and the stamp. The address says where the letter goes. The stamp is the postage: the payment for carrying it. The last part of the address is the ZIP Code, which names the post office or delivery area the address belongs to.
  2. Picking it up. A letter can go in a blue collection box, over the counter at a post office, or in your own mailbox with the flag up. The Postal Service says carriers can pick up mail as they deliver if the flag is up.
  3. Reading the address. At a big sorting building (a processing and distribution center), a machine reads the address and sprays a barcode of tall and short bars onto the letter. Machines can read about 99 percent of addresses now. For the rest, a picture of the envelope goes to people at a center in Salt Lake City, who work out where it should go.
  4. Sorting. Barcode sorters read those bars and send each letter on toward the sorting center for its area. That center is named by the first three digits of the ZIP Code.
  5. The trip. Trucks carry mail between buildings. Mail going a long way often flies.
  6. In order. Near you, a machine sorts the letters for each route into the order the carrier delivers them, house by house. The Postal Service calls it delivery point sequence, or walk sequence.
  7. The last part of the way. The letters go to your local post office, and your carrier brings them to your door.

A few numbers

In 2025 the Postal Service processed and delivered about 361 million pieces of mail a day, or 4,180 a second. On the pages that is “thousands of letters every second”: the count includes cards, magazines and catalogs as well as letters.

It delivers to 170.4 million addresses on 236,347 routes, with about 263,000 vehicles. It flies about 3.5 million pounds of mail a day.

The Salt Lake City center receives about 2.3 million address pictures a day. In the 1990s machines could read fewer than half of addresses. Now they read about 99 percent.

The ZIP Code

ZIP Codes began on 1 July 1963. ZIP stands for Zoning Improvement Plan. The first digit is a large part of the country, from 0 in the East to 9 in the West. The next two are a smaller region, and the last two a particular post office. On the pages, the friend's ZIP Code starts with a 9: far to the west. The addresses on the pages are made up.

Where the pictures stop being true

“It drove right by”
The carrier comes once a day. Carriers are not required to check a mailbox whose flag is down on a day they have nothing to deliver there. In real life the letter would wait for the next day. The truck does not come back the same afternoon.
The flag
Some mailboxes have no flag. Then use a blue collection box or the post office.
One machine
The picture shows one machine doing several jobs. Real sorting buildings have long rows of machines, and the letters ride on their edges, very fast.
“The box for its town”
Close enough. Letters are first sorted toward the right area by ZIP Code, and then more finely. A big city has many ZIP Codes, not one.
The plane
Only mail going a long way flies. Mail going a short way travels by truck.
“Then a machine puts the letters in a line”
That happens at a sorting building near you, before the letters reach your post office. Bigger mail, such as magazines and packages, is often sorted in other ways.
The little lines
The bars go in the lower right corner of the front, a space the Postal Service keeps clear for them. Letters from businesses usually come with a barcode already printed, so the machine reads that one and does not need to print another.

Questions to ask

Before:

  • “Where do you think a letter goes after it leaves the mailbox?”
  • “How does the mail carrier know which house is yours?”

After:

  • “What is the stamp for?”
  • “Why does the flag go up?”
  • “What does the machine do when it can't read the writing?” (It sends a picture to people who can.)
  • “Why are the letters put in the same order as the houses?”

Try it

  • Send one. Write or draw a letter to someone far away, or to yourselves. Let your kid help with the address and stick on the stamp. Count the days until it arrives.
  • Find the little lines. Look at the bottom of today's mail for the row of tall and short bars.
  • Find your ZIP Code. Find it on a letter. Does it start with a small number (East) or a big one (West)?
  • Mail-truck watch. Notice when your carrier usually comes, and wave. Count the mailboxes on your street in the order the truck reaches them.
  • Play post office. Give each room of the house a number. Make letters for each room, mix them up, put them in the order you would walk, and deliver them.

Sending mail from home

Put outgoing letters in your mailbox on the morning the carrier comes, rather than the night before, or take them to a blue collection box.

Where this comes from

Every word, page by page
  1. Look! A letter in your mailbox. It came from your friend, far, far away. How did it get here? Let's find out!
  2. Let's go back to your friend's house. Here is the letter. It needs to say where to go. Tap the letter to write your address. Your name. Your street. Your town. The last part is a number for your town. It is called a ZIP code. A stamp pays for the trip. Tap the corner to stick it on. Thump! Ready to go.
  3. Your friend puts the letter in the mailbox. Here comes the mail truck! Zoom! It drove right by. It did not know a letter was waiting. Lift the red flag. Flag up! That means: a letter is waiting. Here comes the truck again. It stops! The mail carrier takes the letter. Off it goes!
  4. The truck takes the letter to a big, big building. So many letters! Too many to sort by hand. Tap the machine. Click! The machine looks at the address and reads it. Psst! It prints little lines at the bottom. They say where to go. Now tap it again, and sort them all! Whoosh! Each letter goes into the box for its town. All over the country, machines like this sort thousands of letters every second.
  5. Your house is far, far away. So the letter rides in a plane! Drag the plane across the sky. Wheee! It lands near your town, and a truck takes it the rest of the way.
  6. Then a machine puts the letters in a line: the same line as the houses on your street. Drive the mail truck! One, two, three... your house! The letter is home. Look at the bottom of the letter. Little lines! The machine printed them on the way.
  7. Now send a letter back to your friend. Draw a road from your house to your friend's house! You did it! Next time you see a mail truck, wave to the mail carrier.

What did your kid ask this week?

Send it in their own words. We read every one, and the ones we can answer truthfully become the next questions here.

Send their question