Allow emailed invoices to be customized. If we are belatedly charging for an appointment, they receive a receipt that TWICE (once in the subject line, once in the text of the message) contains the date of the processing, NOT the date of the appointment. If people want this, fine, but in an insurance-based clinic people are often charged after the fact for various reasons, and it is very confusing to receive invoices with the wrong date, especially if they need them for reimbursement purposes.