On April 1, 1774, India got its three first postal circles: Bengal, Bombay and Madras. As the date suggests, this was one of first things that the British did once they began to colonise the country.

While Bengal catered to the whole of the eastern and northern regions of British Empire, Madras handled the southern region and Bombay, the rest.

Cut to Independent India. There were now eight Postal Circles: Assam, Bengal, Bihar and Orissa, Bombay, Central, East Punjab, Madras and Uttar Pradesh. But even so, there was confusion over the destination of a letter, given spelling mistakes, places with similar-sounding names, and so on.

It was to streamline the flow of the enormous quantity of mail whizzing around the country that the Postal Index Number – aka PIN Code – system to identify every single post-office in the country with a unique number was introduced on August 15, 1972.

The first digit in the six-digit number indicated the region. The second identifies the sltate or union territory, the third and fourth zoom in on the mail-sorting district within each state, and the fifth and sixth identify the specific post-office whose jurisdiction the address falls under.

The first modern postal codes were introduced in 1932 in Ukraine, which was then under the Soviet Union, only to be abandoned in 1939. It was slowly adopted in the United Kingdom under the name of “postcode” and in the US, as the “zip code”.

While email and other forms of digital communication has cut the number of letters written and posted, e-commerce and home-delivery of purchased products has ensured that the PIN Code remains as important as ever.