World Post Day is celebrated on 9 October every year.

This day is observed to mark the anniversary of the establishment of the Universal Postal Union (UPU) in 1874 in Bern, Switzerland. The UPU was the start of a global communication system that helped different countries send letters and packages more easily across borders. It played a big role in connecting people from around the world.

World Post Day is a reminder of how important postal services are in daily life. Even today, in the age of technology, postal services help deliver mail, documents, and packages. In many rural or remote areas, postal workers are the main link to communication and essential services.

On this day, countries around the world organize different events such as exhibitions, award ceremonies, and awareness campaigns to show the importance of the postal system. The aim is to raise awareness about the role of the postal sector for people and businesses.

The theme of World Post Day changes every year to highlight new goals and challenges. Schools, postal departments, and governments also take part in activities to appreciate the work done by postal employees.

So, the correct answer is 9 October.