OnWorkBeginForPart is a TWorkBeginEvent property that represents the event handler signalled when starting to read or write a message part using the IMAP4 client. 

OnWorkBeginForPart, OnWorkEndForPart, and OnWorkForPart are used internally in the implementation of methods like Retrieve, UIDRetrieve, AppendMsg, AppendMsgNoEncodeFromFile, and AppendMsgNoEncodeFromStream. When assigned, the event handlers are assigned to the TIdTCPStream instance used to read or write the message part for the operation. 

Applications must assign a procedure to the OnWorkBeginForPart, OnWorkEndForPart, and OnWorkForPart event handlers to allow responding to the event notifications.

OnWorkEndForPart OnWorkForPart TIdTCPStream Retrieve UIDRetrieve AppendMsg AppendMsgNoEncodeFromFile AppendMsgNoEncodeFromStream