property DataString: string;

DataString is a string property that represents the contents of the in-memory message part. 

Reading or writing values in DataString causes DataStream to be accessed for the corresponding operation. 

When reading values in DataString, the entire contents of the stream are returned, but the position in DataStream prior to reading values is maintained. 

When writing values to DataString, the contents in DataStream are discarded and set to the new value for the property. 

Use DataStream to access the contents for the in-memory message part as a TStream instance.