Details from customer suggestion:
Suggested customer email types:
Notification (the one you have and are planning to customize)
30 Day Notice (Freshbooks lets you create 3 payment reminders at your own date intervals - each completely customizable)
45 Day Notice
60 Day Notice
Other suggested enhancements
1) You can't customize the greeting or the person that you are sending the invoice too which is important if you have to email the invoice to different people or multiple people and not necessarily the one person that is listed as the Customer contact.
2) Not sure why invoice total and due date are options if they are already locked into parts of the template which cannot be accessed.
3) It would be nice to end the email with a standard signature, but the link is locked at the end of the email. Would be nice to be able to control where the link is in the email.
4) It would be nice to remove "Message:" from the email.