law: 136. Documents exempted from production.-
  (1) Nothing in section 135 shall be deemed to affect the operation of sections 123 and 124 of the Indian Evidence Act, 1872 (1 of 1872) or to apply to any letter, postcard, telegram or other document in the custody of the postal or telegraph authorities.
  (2) If any document in such custody is, in the opinion of any district magistrate, chief presidency magistrate, High Court or Court of Session, wanted for the purpose of any court-martial, such magistrate or Court may require the postal or telegraph authorities, as the case may be, to deliver such document to such person as such magistrate or Court may direct.
  (3) If any such document is, in the opinion of any other magistrate or of any commissioner of police or district superintendent of police, wanted for any such purpose, he may require the postal or telegraph authorities, as the case may be, to cause search to be made for and to detain such document pending the orders of any such district magistrate, chief presidency magistrate or High Court or Court of Session.