Every day, millions of items are posted and delivered by the Royal Mail. With businesses and people nationwide dependent upon the postal service to correctly sort, distribute, and deliver every item, the logistics involved are incredible. Over hundreds of years, the systems involved have evolved to meet the challenge of increasing delivery numbers, using modern technology to increase efficiency and send deliveries their destinations on time.

My aim here is to give you an insight into that process and answer the question, “what actually happens when you post a letter?”


Some important milestones in the history of the postal system:

  • The first semiautomatic sorting machine entered full operation in Rotterdam in 1930, and allowed 15,000 letters to be sorted per hour. This is much higher than was possible with manual sorting. The machine, the Transorma, arrived in the UK in 1935.
  • The United States Postal Service employed the first high speed optical character reader in 1965, which could read addresses reliably enough to handle a preliminary source.
  • The first computer-driven single-line optical character reader was installed, again by the US Postal Service, in 1982. This allowed for a fully automated sort by applying barcodes to letters based on their destination.

As may be expected, the technology involved in the letter delivery process has become increasingly sophisticated over the years. In its infancy the whole process was manual, but the lower amount of letters being sent meant this was manageable.

Though automation is theoretically possible, it depends on no problems arising from the poster’s side. Human intervention in the process is now mostly limited to moving the letters around, and to intervening when the machines are unable to complete their task (when addresses are incompletely written, for example). The vast majority of letters are automatically processed in the UK now – 79% in 2012/13.

The process from the post box

If you were to follow a letter on its journey, the first step would be fairly obvious: the letter is posted. The next step, is being collected by a postal worker (at the collection time advertised on the post box: two collections per day morning and evening, 6 days a week), is probably quite familiar too. Beyond that though, things get interesting.

Your letter is one of hundreds of thousands that are posted each day (in 2012-13, 13,869 million letters were posted, as well as 994 million parcels). That’s a lot to process!

The first step involves separating letters and packages, and is done with the help of a device called the culler (luckily, this isn’t as ominous as it sounds!). The culler is a rotating drum with gaps around the edge that allow small letters to fall through. The letters are taken to the next stage of the process by conveyor belt, while the large packages that don’t fall through the gaps are taken to be manually sorted.

Once the letters are checked for size, the next step of the process can begin. This involves reading the address on the letter, and preparing them for delivery based on their ultimate destination. An ingenious machine detects whether the letter is facing the right way by checking for the ‘scent’ of the phosphor in the stamp – if the stamp side is facing forward, it continues its journey. If the stamp is facing the wrong way, it is flipped to the correct orientation by the machine before continuing.

A high-resolution camera then takes a photo of the address on the letter so that character reading technology can attempt to decipher the address. This software has a high success rate, and can read human handwriting as well as printed text: characters in human handwriting are broken down into their constituent pixels and analysed logically to see which character they are.

At this step in the process, if the address is written particularly messily, or is missing a postcode or other address information, human intervention is required. For messily written addresses a member of staff will read it and skip the letter to the next stage of the process, but if too little of the address is given (sometimes letters only have a name on them!) the letter may be opened by specially trained members of staff who will look for clues to find the identity of the intended recipient.

A sorting code is then applied to the letter based on its address, and it is sorted into a pigeonhole based on its location.

If it is to an address within the delivery radius of the sorting centre, it will be put in a postman’s trolley, but if it is destined for another part of the country, it will be sorted for transport to another sorting centre (the one closest to its destination).

If the letter is bound for another sorting centre before delivery, it will be transported either by van or by plane to the according delivery centre. The next stage is for the letter to be delivered by the trusty local postie. To save them walking backwards and forwards between houses, the letters are sequenced so that they’re in the right order for delivery according to the postal worker’s route.

Next time a letter lands on your door mat or in your post box, take a moment to consider the journey it’s taken to get to you! It’s not unusual for a letter to have travelled a lot of miles, in numerous vehicles, along many conveyor belts, and through any number of machines.

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