Mike,
If the user signed up with your real email address, why did it bounce - shouldn't you have received the confirmation?
ListMail's bounce processing looks for the second "To: " line the the returned email. The first one is of course the bounce target address, ie: bounce@example.com and the second one, since the bouncing message is returned in full, should be the bouncing user.
This detection is being expanded to pass a special header for more accuracy with servers that can return them (60% or so).
If a message to your email address did indeed bounce it would make sense for it to be removed. You should probably just delete such emails instead of bouncing them (I bounce email with MailWasher - you might do the same).
The problem is that I've seen this same email like 5 times, so apparently during the bounce the email address isn't being removed properly, i'd guess bounce isn't setup to handle unconfirmed emails?
Bounce processing should handle any email sent to the bounce address based on the To-line parsing I noted above.
Do you have bounce notification enabled? If so, and you want to look into this further, could you forward the notification you received? You can email it to me at dean@...
Regards