The air mail service from London to India commenced in 1929. The first stage to Genoa, Italy, used an Armstrong Whitworth Argosy, the second to Alexandria, Egypt, was completed with a Short Calcutta Flying Boat and the final stage to Karachi, which was then in India, was covered by a De Havilland Hercules.
This rather excellent image shows us the rear compartment used to carry mail.
Here we see the front baggage area being unloaded. Also, this is the best shot of the pilot on the flight deck that we have seen so far.
The transfer of Royal Mail bags from van to the rear compartment. Air mail was a very important component of the Empire routes and as the following image shows it was available to all with simple procedures.
By the early nineteen thirties the route had been extended to Australia with a further route being added from Alexandria to South Africa.