London: As a hobby, it is esoteric and rather eccentric: setting puzzles for postmen. For the past few years James Addison, 25, a graphic designer who lives in Poole, Dorset, has been sending letters to friends, family, and often himself.

But instead of simply writing the address on the envelope, he has constructed a conundrum for the sorting office of his local Royal Mail postal service to solve.

One address was written in morse code; one was a pencil sketch of the front of Addison’s office building, with the postcode hidden in a street sign; one was constructed entirely as a sonnet. He estimates that he has sent out about 30 such letters and that only two have failed to arrive at their destination.

One of these was a letter that merely had his name — not even his hometown — written on the envelope, so it is not surprising that it stumped the postie. Addison’s hobby has come to light after a video, shot by a friend, was published online. But while his pastime is eccentric, what is even stranger is that the employees of Royal Mail, grappling with cost cutting, appear not to resent his activities. Indeed, they seem to relish the challenge.

“One envelope had three addresses to various friends’ homes with a little biography about each of them,” says Addison. “It invited the Royal Mail to ‘Choose the person who best deserves to receive this letter’. When it arrived, I was surprised to hear that there was a written conversation on the envelope where postal staff across the country had diverted its destination in a sort of debate. The final address had a giant pink heart drawn over it in crayon.”

Even though the rise of email and Facebook means that we are sending only half as many letters as a decade ago, the Royal Mail still handles 45 million a day. Fewer than one in ten of these is a “social communication” as the Royal Mail prosaically describe them.

The great majority are junk mail or business letters, with most arriving on our doormats with a dull, printed address sticker. But all, be they passionate love letters or gas bills — in the first instance — are sorted electronically.

They are sent at high speed through a machine, where a camera scans the postcode. Most postcodes can be read, allowing the letters to be sent to the delivery office closest to the recipient’s address. The final sorting — into the correct village or street so that the postman can deliver it — is done by hand.

There are 1.7 million postcodes in Britain, which means that if a letter has a correct postcode and nothing more, a postman can narrow down an address to no more than about 15 to 20 houses. Most of Addison’s letters did include a postcode on the envelope, though often hidden either within a picture (one appears on a scarf worn by a pigeon) or as part of a clue.

Around 2.4 million addresses a day cannot be “read” by machine. Pictures of them are taken and sent digitally to special offices, manned by 820 staff, who try to decipher where the post should go. When this fails, letters are sent to the National Return Centre in Belfast, whose job is to try to send undeliverable mail back to the original senders.

This office handles about 60,000 letters a day. Eddie Mackenzie, who is in charge of the Western Isles delivery office for Royal Mail, says: “We get an awful lot at Christmas, when people want to send a card and can’t remember where people live. We’ve once had “Home carer, Lady with the horses” and the name of the village, but we were able to work it out.”

Addison insists that he is a huge admirer of the Royal Mail and has no desire to waste postmen’s time.

“The Royal Mail sometimes get a lot of stick. I think it is a brilliant service,” he says. “I don’t think any other postal service in the world would have the commitment to deliver every item they receive.

“I don’t want to annoy the Royal Mail too much and so I avoid Christmas Day, Mother’s Day and Valentine’s Day because that’d probably be the worst possible time to send something.”

He said his most pleasing result was when an address made up entirely of dingbats or pictograms arrived successfully. His surname, Addison, was rendered as a + sign, an E and an image of the sun. A picture of someone diving into a swimming pool was his hometown, Poole.

“I was really surprised that got through,” he says. Although he enjoys solving puzzles himself, he said his hobby was fuelled by a desire partly to test the Royal Mail’s ingenuity and partly to honour old-fashioned letter-writing, following his mother’s advice that a handwritten thank-you note showed you had made an effort.

“I work with computers on a day-to-day basis. I find it quite refreshing to do a handwritten envelope. I think it gives a letter a much more human element.”

He was also inspired by Harriet Russell, an illustrator, who undertook an almost identical project in 1999 when she was an art student in Glasgow. Her efforts — all 130 letters — were turned into a book in 2008, called Envelopes.

The first letter she sent was addressed in mirror writing, and when it arrived back at her flat — in the same time it takes for a normal letter to arrive — she knew that somewhere at the Glasgow Mail Centre, someone had enjoyed her work.

So she pressed on and the results formed the key part of her degree show.

Russell said yesterday that she was very surprised but flattered that she had inspired a copycat artist. Her own favourite envelope was designed as a crossword.

“The postmen had filled in the crossword. I was quite amazed they did it. They really did have to work it out for themselves, even the postcode was an anagram.”

When her publishers approached Royal Mail, it insisted that a rather po-faced warning was included at the start of the book: “This book highlights how Royal Mail postmen and women often go beyond the call of duty to deliver poorly addressed mail. Each week they successfully deliver 15 million badly addressed letters. To help us deliver your post, can we remind you to correctly and clearly address items being posted.”

Even after the Royal Mail was controversially privatised last year, it is still bound by the so-called universal service that ensures that consumers can send a letter to any location within the United Kingdom for a fixed price, with or without a postcode on the envelope. But it helps to have those crucial letters and numbers — even if it is incorporated in a crossword.