Emulate form submission with PHP - php

Question

I am trying to create a link in a PHP generated e-mail to the UPS tracking page. The form on their page for submitting the tracking numbers works like this:
<form action="http://wwwapps.ups.com/WebTracking/track" method="post">
<input type="hidden" name="trackNums" value="'.$returnIn->getOutgoingTrackingNumber().'"/>
<input type="submit" name="track.x" value="'.$returnIn->getOutgoingTrackingNumber().'" class="linkButton"/>
</form>
And if I replicate this on my own site it works fine :)
The problem is if I want to put this in an e-mail... Outlook won't handle forms so I created a link to a redirect page hosted on our webserver like this:
TRACKINGNUMBER
Now on the email_tracking_link page I need to submit this form AND FORWARD THE USER to the page. I can submit the form using cURL or file_get_contents, but this then renders the page within my own site, without any of the CSS styling etc on the UPS page. My code currently looks like this:
if (isset($_GET['ups']))
{
$url = 'http://wwwapps.ups.com/WebTracking/track';
$data = array('trackNums' => $_GET['ups'], 'track.x' => $_GET['ups']);
// use key 'http' even if you send the request to https://...
$options = array(
'http' => array(
'header' => "Content-type: application/x-www-form-urlencoded\r\n",
'method' => 'POST',
'content' => http_build_query($data),
),
);
$context = stream_context_create($options);
$result = file_get_contents($url, false, $context);
}
If I render the form and have the user click the button, then they are forwarded to the UPS page, complete with it's CSS etc. I want this to happen without the user having to click the button...
How can I replicate this behaviour programmatically?