I recently became aware that PayPal's website payments pro doesn't automatically send receipts. I contacted them about how to enable this, and their response was the following.
"Payment receipts are not E-mailed to the buyers using Direct Payment API as the PayPal system does not request an E-mail address from the buyer. This is something that you would need to have your cart or application set up to do so that the E-mail can be triggered by the API response."
Is this something you plan to add to the e-junkie cart?