Gmail provides a unique message ID (X-GM-MSGID) for each email so that a unique message may be identified across multiple folders. The message ID is a 64-bit unsigned integer. This property is set only if server advertises XGMailExtensions1 extension support.

public string GmailMessageId { get; private set; }

Public Property GmailMessageId As String
	Get
	Private Set

public:
property String^ GmailMessageId {
	String^ get ();
	private: void set (String^ value);
}