law: Indian Contract Act, 1872 
  4. Communication when complete
  The communication of a proposal is complete when it becomes to
  
  the knowledge of the person to whom it is made.
  The communication of an acceptance is complete-
  as against the proposer, when it is put in a course of
  
  transmission to him so at to be out of the power of the acceptor;
  as against the acceptor, when it comes to the knowledge of the
  
  proposer.
  The communication of a revocation is complete-
  as against the person who makes it, when it is put into a course
  
  of transmission to the person to whom it is made, so as to be out of the power
  
  of the person who makes it;
  as against the person to whom it is made, when it comes to his
  
  knowledge.
   Illustrations 
  (a) A proposes, by letter, to sell a house to B at a certain
  
  price.
  The communication of the proposal is complete when B receives
  
  the letter.
  (b) B accepts A' s proposal by a letter sent by post.
  The communication of the acceptance is complete.
  as against A when the letter is posted;
  as against B, when the letter is received by A.
  (c) A revokes his proposal by telegram
  The revocation is complete as against A when the telegram is
  
  dispatched. It is complete as against B when B receives it.
  B revokes his acceptance by telegram. B's revocation is complete
  
  as against B when the telegram is dispatched, and as against A when it reaches
  
  him.