ProcessMessage is an overloaded method in TIdMessageClient that implements receiving and processing of message headers and contents from a file with the contents of the Internet message. 

ProcessMessage ensures that the IOHandler for the message client is assigned and initialized for the operation. 

The default implementation of ProcessMessage uses the IOHandler assigned to the client to receive the header and optional body of the message, and stores data in the message instance specified in AMsg. 

AHeaderOnly indicates that the message client will retrieve only the headers for the message, and will not populate the contents of the message body. The default behavior (when AHeaderOnly is False) is to retrieve the entire message including both header and body contents. 

ProcessMessage does not make any assumptions about the contents of the TIdMessage instance in AMsg. In other words, ProcessMessage does not call TIdMessage.Clear before receiving header or body content. The application must call TIdMessage.Clear when reusing a TIdMessage instance for message retrieval.

TIdMessageClient.ProcessMessage TIdIOHandler TIdIOHandlerSocket TIdIOHandlerStream TIdMessage