How to track form submission? (2 replies)

I have a form on my website that sends some parameters to a php script which redirects the user to an external website.
Simplified form:

<form action='/php/handleSubmitForm1.php' method='post'>
  <input id='email' name='email' placeholder='Your Email...'/>
  <input id='category' name='category' value='categoryXYZ' type='text' style='display: none;'/>
  <button id='submitForm1' type='submit'></button>
</form>

Simplified php script example:

$email= $_POST['email'];
$category = $_POST['category'];
header('Location: ' . 'http://exampledomain.com/' . $category . '/?email=' . $email, true, 302);

How can I configure piwik to show me that the user exited to '/php/handleSubmitForm1.php' and maybe even the post parameters?