Add param to drupal mail links for tracking with Google Analytics

mail_customization.module

<?php
function mail_customization_mail_alter(&$message){
   $preg = '/((https?:\/\/)([\da-z\.-]+)\.?([a-z\.]{2,6})?([\/\w \.-]*)*\/?(\?([A-Za-z0-9=&])*)?)/';
   
    foreach($message['body'] as $key=>$body){
      preg_match($preg , $body, $matches);
      
      if (!empty($matches[0])){
        $url = $matches[0];
        
        //If we havent any parameter in the URL
        if (empty($matches[5])){
          $url .= '?'; 
        }else{
          $url .= '&';
        }
        
        $url .= 'source=mail';
        $body = preg_replace($preg, $url, $body);
        $message['body'][$key] = $body;
      }
    }
}