Data type: PtypBinary ([MS-OXCDATA] section 2.11.1)

The PidTagSearchKey property ([MS-OXCPRPT] section is formed by concatenating the ASCII string "EX: " followed by the DN for the object converted to all uppercase, followed by a zero-byte value. This value MUST be present for all Address Book objects on an NSPI server and MUST be in the aforementioned format.

The PidTagSearchKey property is not present on objects in an offline address book (OAB).