Gizmo -
I'm not sure exactly what you're asking? I have a MailEnable mail server that runs on the same machine. It handles sorting the incoming and outgoing mail. I also use Katharion as a third party anti-spam system. It blocks 90% of all mail heading towards our server from ever reaching the server. That reduces our server load immensely.
A minor note for you - in your readme instructions you say:
# New Files #
languages/english/unsubscribe.php
scripts/unsubscribe.inc.php
templates/default/unsubscribe.tpl
You also should add the /languages/english/admin/unsubscribe.php in there.
