Eric, try checking if the actual HTTP POST is happening. If you have some way of intercepting that call, you can see if there is a formatting issue. If you're not seeing any data in the form itself, that would only happen if you have server-side validation enabled (i.e. validation failure page has been set), and your form is set to disregard all submissions if they don't match field requirements (i.e. email address is not in the correct format).
If you don't have a validation failure page, it basically means no data is being sent and you would need to look into connectivity of your application. One quick way to test is to make an equivalent blind form submit link - instructions can be found on this site - and set the POST URL to that from your PHP client.
Regards,
Bojan