law: Indian Post Office Act, 1898 
  8. Power to make rules as to payment of postage and fees
  
  in certain cases
  The Central Government
  
  may, by rule,-
  (a) require the
  
  prepayment of postage on inland postal articles or any class of inland postal
  
  articles, and prescribe the manner in which prepayment shall be made:
  (b) prescribe the
  
  postage to be charged on inland postal articles when the postage is not prepaid
  
  or is insufficiently prepaid;
  (c) provide for the
  
  redirection of postal articles and the transmission by post of articles so
  
  redirected, either free of charge or subject to such further charge as may be
  
  specified in the rules; and
  (d) prescribe the fees
  
  to be charged for the "express delivery" of postal articles, in
  
  addition to, or instead of, any other postage chargeable thereon under this
  
  Act.
  Explanation.- "Express
  
  delivery" means delivery by a special messenger or conveyance.