law: Indian Post Office Act, 1898 
  20. Transmission by post of anything indecent, etc.,
  
  prohibited
  No person shall send
  
  by post- 
  (a) any indecent or
  
  obscene printing, painting, photograph, lithograph, engraving, book or card, or
  
  any other indecent or obscene article, or
  (b) any postal
  
  article, having thereon, or on the cover thereof, any words, marks or designs
  
  of an indecent, obscene, seditious, scurrilous, threatening or grossly
  
  offensive character.