Body is a TStrings property that contains the textual values that make up the body of the message. Body normally contains values when the ContentType for the message is a member of the "text/*" MIME family. 

When ContentType contains a value in the "multipart/*" MIME family, use MessageParts to access one or more TIdText instances that represent the message content. 

When IsEncoded is True, Body contains values that are encoded using the encoding scheme identified in ContentTransferEncoding. 

When IsEncoded is False, Body contains ASCII text that represents the entire contents of the message.

TIdMessage.IsEncoded 

TIdMessage.MessageParts 

TIdMessage.ContentType