|Outlook Developer Reference|
Returns a String value that represents a unique global identifier for the AppointmentItem object. Read-only.
Version Added: Outlook 2007
expression An expression that returns an AppointmentItem object.
In Microsoft Office Outlook 2007, there are situations where the entry ID of AppointmentItem objects may change, such as when an item is moved to a different folder or to a different store. Entry IDs can also change when a user performs certain functions in Outlook, such as exporting and then reimporting data.
Therefore, each Outlook appointment item is assigned a Global Object ID, a unique global identifier which does not change during those situations. The Global Object ID is a MAPI property that Outlook uses to correlate meeting updates and responses with a particular meeting on the calendar. The Global Object ID is the same across all copies of the item.