I am trying to implement a custom Tracking Pixel for Emails sent out from wordpress.
Thanks to these post:
Tracking email with PHP and image
Tracking email opens with a real image
and especially
http://www.phpdevtips.com/2013/06/email-open-tracking-with-php-and-mysql/
I was able to implement the core idea.
The email loads the tracking pixel via
<img src="https://www.example.com/tracking.php?order_id=1" width="100" height="100" />
and in the tracking.php
$graphic_http = 'https://www.example.com/GIF-example.gif';
header('Content-Type: image/gif');
readfile( $graphic_http );
Opening the tracking.php file in a browser opens up the gif image for download.
However the Tracking pixel/Tracking image doesn't show up in the Gmail Email. There is only a broken image logo and when I click to show the image this link is opened
which states a Google 404:
Google 404. That’s an error.
The requested URL /proxy/l2xUKFGnNFKm64zEYmJhOcUmEJm15w9MC1txRRF01tpKlcL3t3O16aMJgbYQkucBySV0xV2T0EsCwikOAC0Z4em6uPzSs38lkHrYBvosRRAk14EfPoEXqC5JdLxRm8ToZmGSQqt_RwHCaBE_3uLgQDVEB05Rdtkq-Xzuw30=s0-d-e1-ft was not found on this server. That’s all we know.
It seems to be a problem that Google's proxy cannot read the php script. Both the tracking.php and the GIF-example.gif files have 775 rights and are accesible publicly.
On Hotmail this does work so it really seems to be a problem with the Google Proxies.
Does anybody know how to let the Google Proxies access this Tracking pixel?
I figured out the answer: The problem was with the Google Proxies and the question mark ? in https://www.example.com/tracking.php?order_id=1
The Google Proxies address got messed up because it already had a question mark and resulted in a 404.
I resolved it using https://www.example.com/tracking.php/order_id=1 instead and then on the tracking.php I didn't use $_GET but $_SERVER['REQUEST_URI'] and parsed the /order_id= String.
The tracking pixel shows up in Gmail and it gets tracked in the tracking.php script.