The property gets or sets the property tag without the type part of the tag.
Assembly: EWS (in EWS.dll)
The property can be represented as either a hexadecimal or a short integer.
The range between 0x8000 and 0xFFFE represents the custom range of properties. When a mailbox database encounters a custom property for the first time, it assigns that custom property a property tag within the custom property range of 0x8000-0xFFFE. A given custom property tag will most likely differ across databases. Therefore, a custom property request by property tag can return different properties on different databases. The use of the property is prohibited for custom properties. Instead, use the PropertySetId property and the PropertyName or PropertyId property.
Access any custom property between 0x8000 and 0xFFFE by using the GUID + name/ID.
You cannot use a property tag for properties within the custom range 0x8000-0xFFFE. You must use a named property in this case.