ReceiptRecipient is a TIdEMailAddressItem property used to identify the address where a return receipt for the message should be delivered. The values in ReceiptRecipient are used in the RFC 2822 message header "Disposition-Notification-To:". A blank value in ReceiptRecipient indicates that a return receipt is not desired. 

Use the following properties to get or set the values for the TIdEMailAddressItem: 

Including an email address in ReceiptRecipient does not guarantee that a receipt notice will be generated when the message is received; the recipient can always cancel the request.

TIdMessage.Sender 

TIdMessage.From 

TIdEMailAddressItem