In version 18.6 (2023) we expanded this functionality in multiple ways. You will now be able to create your own Email Message IDs specific to Cash Receipts and edit the email address and email message per transaction with the added E-mail Detail Entry window.
From the Customers Navigation List, to make it easier to setup, we added the Cash Receipts selection to the Mass Customer E-mail setting window to mass update customers for emailing Cash Receipts.

There is a new Doc. Type option specific to Cash Receipts for creating E-mail Messages that will allow you to customize the subject and body and pull fields from your specific Cash Receipt transaction onto your E-mail to the customer.
The Cash Receipts Entry and Inquiry windows now have the email detail icon next to the Customer ID to add and edit E-mail addresses and Email Message contents.
