Read Receipt
Request that a read receipt be returned by the recipients of the message when they view it.
Delivery Success
Request that the destination mail server send back a status message when the message is successfully delivered to each recipient.
Delivery Failure
Request that the destination mail server send back a status message when the message fails to be delivered to any recipient.
Delivery Delay
Request that the destination mail server send back a status message when the message is delayed when being delivered to any recipient.
Return Entire Message
Request that the returned status message should include the entire contents of the original message rather than just the headers.