A postal code is the alternity of letters or numbers that are added to the postal address with a specific purpose of sorting and facilitating the distribution of correspondence. This can happen and automatically. To date, most national postal services use certain postal indices. Based on the Law of the Russian Federation, the postal digital designation of the mailing address is called the postal index, which is assigned to the postal object. To date, the index is used to sort letters. The scanner reads the city index, after which he lies where he needs. Therefore, the index is written by special lines that most of the numbers were similar. Many handwriting are different, and the computer will not be able to recognize everything. The index is a city code to be able to fly away to where it should. You can give an example, you have an index of the Vladimir region – 600,000, and you need to smash a thousand envelopes in alphabetical order simply unrealistic. But if you have this number, then you will without much effort determine how you need the area. According to these numbers, you can build the area in the desired chain, after which after analyzing and rationalizing the bypass of all addresses. A postcode is simply necessary in our time, because every day millions of letters go from one corner of the world to another. Without such a system, not a single person in the world received his mail in time, because an automatic set is the best that they could come up with. By the way, and the discoverers of this phenomenon are our compatriots back in 1932. In Europe, the index is written differently than in Russia. But the most important thing is that in the end everyone receives their mail on time, and all this thanks to the modern automatic mail index.