You're probably right. This module is intended for centralized authentication between Drupal and Postfix. If you just need to send Drupal alerts, it should work out of the box. You may want to monitor the mail log:
sudo tail -f /var/log/mail/mail.log
If the mail is actually being sent, check the anti-spam folder. If the mail is not being sent, check your Drupal site configuration. The Drupal log will help.