hi Jon,
I'm not sure whether this could help, but some of the lists I am subscribed to, send periodically an email to all subscriptors, reminding them that they are subscribed and how to unsubscribe.
You could use a simple shell script to do the job. It should send a customized message to each address in your list, and the message should include the subscribed address (ie, the one in your list) and a note instructing the user to bounce back the message in case they cannot unsubscribe by themselves. That way you should know which address to remove.
Miquel
Hi People
I use Smartlist to maintain a large list for newsletters. However because of mail forwarding some recipients cannot get off the list automatically and I cannot figure out how they got the email.