First create the message in Notepad and save it as an "All file **" document.
Open "Messages" from your toolbar, select "Create Rule for Message".
In the first box tick and select "all messages".
Then in box 2 select "Reply with message".
In box 3 select "message" (this will be underlined in blue). Navigate to the previously created message and open it, the message will then be attached to all out going emails.