try some access restrictions

zimbraAddressAvailable.php

@@ -1,7 +1,7 @@
 <?php
 define('IS_AJAX', isset($_SERVER['HTTP_X_REQUESTED_WITH']) &&      strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest');
 if(!IS_AJAX) {
-    die('Restricted access');
+    die(print_r($_SERVER));
 }
 $pos = strpos($_SERVER['HTTP_REFERER'],getenv('HTTP_HOST'));
 if($pos===false) {