Section 25B(3)(b) in The Delhi Rent Control Act, 1958
(b)When an acknowledgement purporting to be signed by the tenant or his agent is received by the Controller or the registered article containing the summons is received back with an endorsement purporting to have been made by a postal employee to the effect that the tenant or his agent had refused to take delivery of the registered article, the Controller may declare that there has been a valid service of summons.