Problems with tracking pixels and Gmail proxy

Question

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

https://ci5.googleusercontent.com/proxy/l2xUKFGnNFKm64zEYmJhOcUmEJm15w9MC1txRRF01tpKlcL3t3O16aMJgbYQkucBySV0xV2T0EsCwikOAC0Z4em6uPzSs38lkHrYBvosRRAk14EfPoEXqC5JdLxRm8ToZmGSQqt_RwHCaBE_3uLgQDVEB05Rdtkq-Xzuw30=s0-d-e1-ft#https://www.example.com/tracking.php?order_id=1

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?

Answer 1

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.