When the
Great Indian Peninsular Railway completed the construction of the Bombay - Jabalpur Railway line via
Thull Ghat and
Itarsi in 1870, it provided the earliest direct connection from
Bombay to
Calcutta via
Allahabad. The inaugural service of the Calcutta Mail was started at 7 March 1870, and the inauguration was attended by The Duke of Edinburgh, the
British Viceroy Lord Mayo and the Governor of Bombay, along with the Maharajahs. The train would initially cross the Thull Ghat from Bombay towards Jabalpur and Allahabad, where it would reverse and travel towards Patna to Howrah. After opening of the
Howrah - Gaya - Mughalsarai line, the train was diverted to run via Gaya. The train was initially run by
East Indian Railway as a passenger service with mail coaches attached. From the 1890s, to address the quick movement of mail between Bombay and Calcutta, several postal special trains were run by
GIPR and EIR. The
Imperial Indian Mail was the most famous of these trains, running alongside the Calcutta Mail on a weekly basis. Difference was while the Calcutta Mail would start from
Victoria Terminus, the Imperial Indian Mail would start from
Ballard Pier Mole railway station because it provided a connection to the British tourists arriving by ships towards Calcutta, the then capital of British India. While the Calcutta Mail would travel to and reverse at Allahabad, the Imperial Indian Mail would instead take the Allahabad Chheoki bypass towards Mughalsarai. The Calcutta Mail served all types of passengers along its route, while the Imperial Indian Mail, with its First Class and Restaurant Cars, were catered more to the British tourists and was the pinnacle of luxury at the time. Due to World War II, the Imperial Indian Mail along with Calcutta Mail was shut down for service, for an indefinite period of time. When the war ended in 1945, regular service resumed for the Calcutta Mail, which is the current iteration of the Howrah Mumbai Mail. This train's name was changed to Kolkata Mail to avoid confusion with the
Mumbai Mail via Nagpur, though now it is named as the Mumbai Mail, same as its other counterpart. Maintenance and operation of this train went to
Eastern Railway after its formation in 1952. The train numbers, from its inception in 1870, were kept as 3 UP from Howrah to Allahabad and 4 DN from Allahabad to Howrah; numbers would change in
GIPR as 7 DN from Allahabad to Victoria Terminus and 8 UP from Victoria Terminus to Allahabad. This continued till 1989, when the 4 digit numbering scheme prompted the change of train numbers from 3 UP / 4 DN to 3003/3004 from Howrah to Bombay. After its conversion to
Superfast Express, numbers were changed again to 2321/2322. In 2010, due to the 5 digit numbering scheme directive, train number was again changed to its current numbers, 12321/12322. On 1 April 2016, the Kolkata Mail was diverted permanently to run via
Allahabad Chheoki instead of taking reversal at
Allahabad. This has led many to confuse the Kolkata Mail with the Imperial Indian Mail, which used to do the same. == Timings ==