law: Indian Post Office Act, 1898 
  40. Duty of master of ship, departing from any port in
  
  India and not being a mail ship, to convey mail bags 
  The master of ship,
  
  not being a mail ship, about to depart from any port in 5[India] to
  
  any port within, or any port or place beyond, 5[India], shall
  
  receive on board any mail bag tendered to him by any officer of the Post Office
  
  for conveyance, granting a receipt therefor in such form as the Central
  
  Government may, by rule, prescribe, and shall, without delay, deliver the same
  
  at the port or place of destination.