How Mail Sorting Uses Postcodes

When you post a letter, the postcode is the part that lets the postal network decide where it goes next, often without a person reading the rest of the address. Each step of the journey uses a different part of the code.

Collection and first sorting

Mail is collected from post boxes, post offices and businesses and taken to a sorting centre. There, automated equipment images each item and tries to read the address, paying particular attention to the postcode. Items that machines cannot read are passed to people, which is slower.

Routing between centres

The first part of a code usually identifies a broad region or sorting area. Using it, the item is sent onwards to the centre that serves the destination. This stage is why a letter to a far-away city can move quickly overnight: the system only needs the broad part of the code to decide the next hop.

Narrowing down to a round

At the destination centre the finer part of the code is used. Items are grouped by the delivery round or walk that covers that small area. Some operators then print a machine-readable barcode that encodes the code, so later sorting can happen without reading the address again.

Final sequencing

In some systems, mail is arranged in the order the carrier will walk or drive. The carrier then uses the street name and house number, not the postcode, to find the exact door. The postcode got the item to the right round; the rest of the address takes it the final steps.

Why accuracy matters

A wrong digit or letter can send an item to the wrong region, where it must be caught and redirected. A missing code forces manual work. Getting it right the first time is simple, and the guide to common postcode mistakes shows what to watch for.

Where it fits

Mail sorting is the original reason postcodes exist, as told in the history of postal codes. The way a code is built, with a broad part followed by a narrower part, is explained in postcode structure explained.