188.8.131.52 PidTagReadReceiptSearchKey Property
The PidTagReadReceiptSearchKey property ([MS-OXPROPS] section 2.875) contains an address book search key, as specified in [MS-OXCDATA] section 184.108.40.206, that represents the user to whom a read receipt is directed. This property is only used and validated if the PidTagReadReceiptRequested property (section 220.127.116.11) is set to 0x01. The property can be absent, in which case the PidTagReportSearchKey property (section 18.104.22.168) is used as an alternative. If neither property is present, the PidTagSenderSearchKey property (section 22.214.171.124) is used to identify the user who receives the read receipt.