Settings > Settings Window - Company > Settings Window - Company > Email > Edit Your Default Message for Emailed 
Forms
                                
                                Edit Your Default Message for Emailed Forms
To edit the message that appears on emailed forms:
- In the Home window, on the Setup window, choose Settings.
 - On the left side of the window, click Company and then Email.
 - Select invoice, receipts, statements, or bill confirmation from the Form list, and modify its default message in the Message for area.
 - Click OK.