Multiple order confirmations

Hi,

after hitting the ‘buy now’ button within the checkout, I get a popup to switch to the ratenkauf website.
After confirming the popup, the customer will already receive a order confirmation mail, even if it is not paid yet (or even checked by ratenkauf).

Also, if the user uses the ‘back’ button on the browser, he will be redirected back to the shop checkout (which is the expected behavior). But then, when again using the ‘buy now’ button, the user will receive the very same order confirmation mail like before. Thus, the user can receive multiple order confirmation mails (which may or may not result in spam detection and therefore server ip blocking by some mail providers).