Thanks for tagging me in this. Due to various older theories and unsubstantiated claims flying around the internet, the whole 'oldest train of India' discussion has become very muddled.
Based on our search for the past few years, as of now, the oldest known services running on IR as below -
1) MAS - MAQ mail - Started as the Madras-Beypore...
more... 'South-West' mail on 5th May, 1862. Overtime, it was extended to Calicut and later to Mangalore. In 1929, the MAQ mail and the Mettupalayam mail were sped up and renamed as 'Malabar express' and 'Blue Mountain express' respectively.
However, after Independence, due to local demands, the name Malabar express was given to the MAQ-SRR/ERS express (which still has the same name today). The Malabar express of today and the MAS-MAQ mail are completely unrelated.
2) Gujarat mail - The Bombay-Ahmedabad Gujarat mail commenced running from December 26th, 1864. This train's history is well documented.
3) Bombay-Calcutta mail (via Itarsi) - While the exact details are a bit complicated, for all practical purposes, the Bombay-Howrah mail service via Itarsi started from 1st April, 1870. This train is NOT the Imperial mail. The Imperial mail was a completely different train that ran for a short time between 1926 and 1940.
I've updated the Wikipedia page for the Imperial mail -
click here but somebody seems to have created a new page for the Howrah mail and added some wrong information there. I'll correct it.
4) Bombay-Madras mail - The through service between Bombay and Madras via Raichur started from 1st January, 1872. It has remained relatively unchanged over the years.
More in the next post.