PayPal IPN Problem

This is really basic but:

If I send an IPN test (via the PayPal IPN test tool) to a script url 开发者_Go百科that simply triggers a generic email to me.

Shouldn't that send me an email?

I just want to make sure that I am not ignorant about something simple here. But If PayPal is really touching that script, it should fire off the email right?

PayPal IPN test tool says it is getting a failure and describing it as a code 500. But my host says ports are open and working fine. I can browse to my script with a browser and it triggers the email.

Any ideas what I am missing?

The code in my listener is simply one line that sends me an email:

<?php
    mail($this->tech_email,'Requested Before POSTBACK',"Here you go");
?>

I am just trying to make sure PayPal is actually calling this url. Doesn't appear to be.