XEP-0184: Message Delivery Receipts

http://xmpp.org/extensions/xep-0184.html

"While Advanced Message Processing [1] provides message acknowledgements at the server level, it does not extend that model all the way to the client. [2] However, sometimes client-level acknowledgements are needed, for example to provide "receipts". This document defines a mechanism for XMPP message delivery receipts, which are functionally equivalent to the "delivered" or "displayed" event in Message Events [3], which this specification in part obsoletes."