Can someone confirm this? - On a Customer Payment, I have the option to Save & Email... but there is no field on the form with "to be emailed" checkbox/a place to enter an email address?

What I did is to check the USE POPUP FOR MAIN TRANSACTION EMAIL BUTTON in the Email Preferences so I can edit the entire email before sending. Then, customize the customer payment form to display the Email Action as Button instead of Menu (to enforce the preference).