Perhaps the Listserv could detect a mail sent by a mailer and see if it was a mail delivery error, then take the apropiate actions to delete the user, inform the list owner, or report it to the listserv manager. We have a local server here and this seems to work well. And why not to have listser to define it's sender tags with: Listserv 1.6 for list "LSTSRV-L", or with the list owner address? After all the sender is the one who sends the mail, or I'm wrong?. Well this is only a comment. -Alejandro Disclaimer: A bunch of characters to fill the bandwith.