MessageEncoderInfo is a TObject property that represents encoder information for the message parts collection. MessageEncoderInfo is updated to reflect the coder need to represent the
AttachmentEncoding. MessageEncoderInfo is used in
TIdMessage.GenerateHeader to initalize headers for a message based on the encoding schema. MessageEncoderInfo is also used in
TIdAttachment.Encode to instantiate an encoder for writing an attachment to a stream.