A Message Converter is invoked for every message or each message part going through the server. The Message Converter may leave the message part intact or modify or remove the message part. The text parts are processed as Java String Objects. The Message Converter processes other attachment as a stream of bytes and returns a potentially different stream of bytes, or nothing at all if the attachment is to be removed.
The applications that uses Message Conversion API include the following:
Virus checking and removal
Translation engine integration
Message content filtering