The post office handles most of the city's inbound and outbound mail and parcels.

An alley beside the post office was the site of the guardhouse that housed the infamous 1756 Black Hole of Calcutta (1756).

The General Post Office was designed in 1864 by Walter B. Grenville (1819-1874), who acted as consulting architect to the government of India from 1863 to 1868.

Recently a marble plaque has been installed on the Eastern walls of GPO, which highlight the Brass Plate.

The GPO is notable for its imposing high domed roof (rising over 220 feet) and tall Ionic-Corinthian pillars.