What is a non-read report?

In this article on MSDN the message classes for email are开发者_如何学Python explained. It states that the prefix "REPORT" indicates an automated message and the subtype is defined in the suffix:

• DR: Delivery report
• NDR: Nondelivery report
• IPNRN: Read report
• IPNNRN: Nonread report

Now I ask myself: does this last type even exist because how would you ever get a report of someone not reading an email? E.g. if you dismiss the "send read receipt" dialog in Outlook, nothing happens. It just doesn't send the 'IPNRN'. Right?

If it does exist, how can I trigger one?

IPNNRN stands for The Interpersonal Note Non-Receipt Notification. Non-read receipts are similar to read receipts, only they inform a sender that a recipient deleted a message without opening it. Non-read receipts are generated by the messaging client of the recipient, not a mail server.

I found this explanation from an Exchange 2003 tech manual.

I don't know what e-mail clients can be configured to send these, but you can experience this using Outlook. If you sent an e-mail with a standard read-receipt request to an Outlook client that had automatic read-receipt response turned on, and the client deletes the e-mail without reading it, Outlook will send a IPNNRN back to the sender.