refactor getting mail auth

src/boxerror.js

@@ -50,6 +50,7 @@ BoxError.INTERNAL_ERROR = 'Internal Error';
 BoxError.INVALID_CREDENTIALS = 'Invalid Credentials';
 BoxError.LICENSE_ERROR = 'License Error';
 BoxError.LOGROTATE_ERROR = 'Logrotate Error';
+BoxError.MAIL_ERROR = 'Mail Error';
 BoxError.NETWORK_ERROR = 'Network Error';
 BoxError.NGINX_ERROR = 'Nginx Error';
 BoxError.NOT_FOUND = 'Not found';