I'd be glad to help share information about customizing the Customer Sales Report in QuickBooks Desktop Point of Sale.
The ability to add the customer email address field on the Customer Sales Report is not yet available as of the moment. However, you may export the report to Excel and manually add the customer's email address from there.
On the other hand, I'll take note of this and pass along the suggestion here on my end. In this way, our product developers will be able to know your preference when running the Customer Sales Report.