That is what I thought was also happing at first. 

We actually have sign-on/sign-off web pages and I thought people were mistyping their email address but when i checked the last 20 messages from last week not one of the bounced addresses have a similar email on the list. I checked against the changelog table just to be sure they didn't exist sometime earlier as well.

The only thing I mentioned to the list owner was to modify the sign-up/ sign-off page to use one of those graphics that a physical person needs to type the phrase into a textbox. but that would only solve if there was some sort of bot or program that is entering dummy info and submitting the form. I guess there is not much we can do if someone is spamming the "listname-signoff or listname-unsubscribe address" as Nathan pointed out. 
  ----- Original Message ----- 
  From: Valdis Kletnieks 
  To: [log in to unmask] 
  Sent: Wednesday, August 29, 2007 1:53 PM
  Subject: Re: Frequent Bounce Backs


  On Wed, 29 Aug 2007 09:54:25 EDT, Mike said:
  > As I said the owner receives 3-4 per day. Is this a spammer who is
  > trying to send sign-off requests for random email addresses?

  I often easily see 3-4 a day of the following:

  1) User subscribes as [log in to unmask]
  2) User gets new account [log in to unmask], forwards cheapmail.com mail there.
  3) user gets [log in to unmask], resets his forwarding on cheapmail,
  and closes down newmail.com

  4) User goes to unsub, remembers they subbed under an old address, and sends
  the now-dead newmail.com address rather than the even older but still working
  cheapmail.com address.

  *usually*, looking at the From: for the unsub and likely near-matches on the
  list will show what's going on.  If that doesn't flush it out, the list owner
  can always post a monthly reminder "Unsub from the address that was actually
  subscribed" and see if that helps...

  Or are the From: addresses totally and obviously bogus or otherwise not
  possibly just user errors?