Since 1969, October 9th has been celebrated as World Post Day. This day was chosen as it coincides with the establishment of the Universal Postal Union or UPU in 1874. The UPU is an agency of the United Nations and one of the first created. Its job is to help improve the quality of the postal service of the member countries as well as co-ordinating postal policies.
World Post Day is marked by at least 150 countries around the world, with an essay contest for young people, new stamps, commemorative postmarks and philatelic exhibitions among other events. Read more about the holiday
These are a few examples of the stamps issued commemorating World Post Day this year from Malaysia, Thailand and Hong Kong. Hong Kong also has special postmarks for the day, have a look:
How are you going to celebrate World Post Day? I'm writing up a storm today, enjoying a cup of tea and the beautiful Autumn view out my window as I compose my letters.