Return Receipts
If I request a receipt when sending a message, I want

A delivery receipt from the receiving server (DSN)
A read receipt, notifying me when recipients display the message (MDN)
Both types of receipt

When a receipt arrives

Leave it in my Inbox
Move it to my Sent Mail folder

When I receive a message and the sender requested a receipt (MDN)

Never return a receipt
Return receipts for some messages