The first Post Office was materialized by King Rama V’s brother.
In 1883, the business started by using the old building built in 1871 located by the banks of the Chao Praya River near the future Memorial Bridge. The building once belonged to a ruler of Muang Pracheen Buri (now, Pracheen Buri Province).
The ruler was convicted of a serious crime, killing and torturing a lot of Siamese residing in Krabin Buri District. He was sentenced to be executed in 1879. All of his property including his big house was seized to be the government’s asset. It later was renovated and used as the first Post Office (Not sure of the right English term. I saw various).
In 1927, the part of the business focusing on post office was moved to the former location of the British Embassy on Charoen Krung Road (New Road).
Being merged with the telegraph business, it became the General Post Office.
This was a logical step to have Bangkok’s ‘all in one’ post and telegraph office in this area because the road had served for many decades as a settlement for farung traders, with goods being transported by boats on the river.
The office used this original building until 1939, then it including all other buildings around was demolished and the new building with new space and new name "Post & Telegraph Department", as we see at present, was constructed on the same area.
(A comparison between the British Embassy and the Post and Telegraph Department on the same area)
Today, the building remains functioning as one of Thailand’s post offices which provides postal services to the general public, and a portion of the building now houses the Thailand Creative & Design Center (TCDC).