Based on the diagram, it is clear that such a file will follow a simple path of email/save. It will allow the user to save the email for future reference. Other paths use the email in different means. Some paths can be used to send it forwards. Others can be used to transfer it to the inbox. Still other paths can be used to work upon.
Simply modifying the route by a deflection of the command can help you direct the email to different purposes. This is a convenient means of manipulating the system and is a primary set of commands that every Linux user must know.