As applied to email, the term return receipt is somewhat ambiguous or misleading. In particular, when delivering a message to a recipient's computer system, which is controlled by that recipient or someone acting on his behalf, there is no way to prevent that computer system from making the message available to the recipient without issuing an acknowledgment to the sender.
This is in contrast with a physical delivery medium in which a courier acting on behalf of the sender can honor the sender's requirements for delivery - up to and including hand-delivery of the message to the recipient and requiring that recipient to authenticate himself to the courier before receiving the message. This difference in capability between physical delivery systems and electronic mail causes confusion and misunderstanding. For this reason, many experts eschew the term return receipt in connection with email, in favor of less ambiguous terms.
Two notification services exist in Internet mail that are similar to return receipts in the physical world. One is called Delivery Status Notifications or DSNs, and the other is termed Message Disposition Notifications or MDNs.
Read more about this topic: Return Receipt