try new mailboxcheck

zimbraAddressAvailable.php

@@ -6,7 +6,7 @@ if(substr($host, 0 - strlen($allowed_host)) != $allowed_host) {
 }
 
 define("CLIENTAREA", true);
-require_once(__DIR__ . '/../../init.php');
+require_once(__DIR__ . '/../../../init.php');
 use WHMCS\Database\Capsule;
 
 $whmcs = App::self();