188.8.131.52.6 Read Receipt
To generate a Disposition-Notification-Toheader (2), clients set the PidTagReadReceiptRequested property ([MS-OXOMSG] section 184.108.40.206) to "TRUE" and also set the values of either the PidTagReadReceipt property group (section 2.6.1) or the PidTagSentRepresenting property group (section 2.6.5).
MIME writers check the PidTagReadReceiptRequested property value first. If the property is not set or the value is "FALSE", MIME writers MUST NOT generate the Disposition-Notification-To header (2).
If the PidTagReadReceiptRequested property is set and its value is "TRUE", MIME writers generate the Disposition-Notification-To header (2) from the PidTagReadReceipt property group, if that property group is set. The order of preference in that property group is as specified in section 220.127.116.11.1. If the PidTagReadReceipt property group is not set, servers SHOULD generate the Disposition-Notification-To header (2) from the PidTagSentRepresenting property group.
MIME writers MUST generate the Disposition-Notification-To header (2) as specified in [RFC3798].
When generating a TNEF message, MIME writers SHOULD<17> also copy the values of the PidTagReadReceiptRequested, the PidTagReadReceipt, and the PidTagSentRepresenting property groups to the attMsgProps attribute, as specified in [MS-OXTNEF] section 18.104.22.168.21, in the TNEFbody part.