Authorize.net Email sent to Customer

I just got off the phone with Authorize.net and they are saying that the issue I am having is something possibly rather simple within the code of Marketpress. When the customer buys a product, they get a very well versed email from us through Marketpress. Then they get an email from Authorize.net verifying the purchase. I don't want them getting two emails, so the second one from Authorize.net has to go. I went on Authorize.net and unchecked the "send email to customer" box, but it still sends them. Then I called them and they said this is something I need to talk to with the developers, as it is something in the code that is overriding the unchecked box that needs to change. Do you guys know the code that can be changed and where to change it?