Do you have any other emailing pages on your site that are working correctly like a registration page or a contact form? Have you ever had a email script on the site that worked correctly? I'm trying to see if there is a potential problem with the settings that are being used or if the issue is specific to the receipt email. Also, if you could post a copy of your confirm page minus the sensitive details for your gateway I can take a look at the code to see if there is something that is just not allowing the email to run.