2.2.2.2.1.11 PidTagMessageSizeExtended Property
Type: PtypInteger64 ([MS-OXCDATA] section 2.11.1)
The PidTagMessageSizeExtended property ([MS-OXPROPS] section 2.798) specifies the 64-bit version of the PidTagMessageSize property (section 2.2.2.2.1.10).