try new mailboxcheck

zimbraAddressAvailable.php

@@ -7,6 +7,8 @@ if(substr($host, 0 - strlen($allowed_host)) != $allowed_host) {
 
 define("CLIENTAREA", true);
 require_once(__DIR__ . '/../../../init.php');
+require_once("api/Zm/Auth.php");
+require_once("api/Zm/Account.php");
 use WHMCS\Database\Capsule;
 
 $whmcs = App::self();