Email as proof of expense

I recently purchased a gift voucher via a business website (a restaurant in this case) and did not receive an invoice from it. I did receive an email containing all the details. It states that it concerns an order for a gift voucher, the cost price, that it was paid for by Bancontact and my details, including my address and vAT number. Is this email sufficient proof of the expense if I print it out as a pDF and upload it, or do I actually need an invoice?