$xmlapi = new xmlapi('MY IP Address');
$xmlapi->password_auth("root",'My Cpanel password');
$xmlapi->set_output("json");

$xmlapi->set_debug(1);
print $xmlapi->api2_query($account, "Email", "listpopswithdisk" );

{"cpanelresult":{"apiversion":"2","error":"Access denied","data":{"reason":"Access denied","result":"0"},"type":"text"}}