Return receipt
An e-mail that is automatically sent back to the sender when the recipient has read or otherwise viewed the e-mail. This allows the user to know that an e-mail has been received and read.
In order for a return receipt to work properly, the e-mail program that the recipient is using must support this feature and must have it enabled. Finally, many programs that have this feature will also prompt the user before sending a return receipt, if the user does not select to return a return receipt you will not get one.