Removes the flags specified by MessageFlags from the messages specified by MessageSet .
Examples of possible flag values are server dependent, but can include:
|\Deleted||Mark a message as deleted (for removal by later ExpungeMailbox).|
|\Seen||Mark a message as read.|
|\Answered||Mark a message as answered.|
|\Flagged||Mark a message as flagged.|
|\Draft||Mark a message as being incomplete (under composition).|
This method returns a result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message. (Note: This method's result code can also be obtained by calling the GetLastErrorCode() method after it returns.)