188.8.131.52.7 PidTagChangeKey Property
Data type: PtypBinary ([MS-OXCDATA] section 2.11.1)
If the last change to the messaging object was imported from the client by using the RopSynchronizationImportMessageChangeROP (section 184.108.40.206.4.2), the value of the PidTagChangeKey property that is saved to the message store by the server contains the value for the PidTagChangeKey property that was passed in the PropertyValues field of the RopSynchronizationImportMessageChange ROP request buffer.
If the last change to a messaging object was made by the server, the value of the PidTagChangeKey property that is saved to the message store by the server contains an XID generated from the PidTagChangeNumber property (section 220.127.116.11.3). For more details about generating XIDs based on internal identifiers (2), see section 18.104.22.168.