law: Indian Post Office Act, 1898 
  42. Allowance of gratuities for conveyance of postal 
  
  articles by ships other than mail ships
  The Central Government
  
  may, by notification in the Official Gazette, declare what gratuities shall be
  
  allowed to masters of ships, not being mail ships, in respect of postal
  
  articles received by them for conveyance on behalf of the Post Office; and the
  
  master of a ship, not being a mail ship, about to leave any port in 5[India]
  
  as aforesaid shall, if he receives on board a mail bag for conveyance, be
  
  entitled to demand and obtain immediately the amount of the gratuity payable
  
  under this section in respect of the mail bag and its contents.