DataStream is a TIdStream property that represents the stream used to access the contents of the in-memory message part. 

DataStream is the stream returned by the OpenLoadStream method, and used to access the contents of the in-memory message part during encoding and subsequent transmission. 

DataStream is updated in PrepareTempStream and FinishTempStream when loading or receiving an in-memory message part. 

DataStream is allocated in Create, and freed in Destroy. 

Assigning a new TIdStream instance to DataStream causes the contents of the new stream to be copied to the DataStream property. 

Use DataString to read or write the contents of the in-memory message part as a String value.

TIdAttachmentMemory.DataString 

TIdAttachmentMemory.OpenLoadStream 

TIdAttachmentMemory.CloseLoadStream 

TIdAttachmentMemory.PrepareTempStream 

TIdAttachmentMemory.FinishTempStream 

TIdAttachmentMemory.Create 

TIdAttachmentMemory.Destroy