I receive the download email when testing but not with a live order

There are a number of reasons why the download email will not be sent with live orders even though it works with the test form or manual order form. First of all check for an error message on the return to your site after paying. This should show any problems in the settings. If the download page is working fine then check that you have IPN in your Paypal account pointing to

and not linklokipnret.php which is for auto return only.
Also check that the the item number in your Paypal button matches exactly the product id in linklokipn.php.