Gmail read receipts feature notifies the sender with automatic acknowledgement when the receiver read the mail. Presently this feature is available only in google apps for Business and Government editions.
This feature is very useful for Business and Government users as they need to know whether the information (mail or attachment) has received to the correct person in time or not.
To enable this feature login to administrator control panel. Then you can see the option Email read receipts there. For more steps wise help visit help center.