Hi,
You need to run Consoleone or NWAdmin and go to the GWIA and open properities, look for the Tab SMTP/MIME and open Undeliverables. You can remove the check mark from the Move to Problem Directory box there, that will stop the messages. The messages will just be discarded after that??
So I don't think this is a very good option to turn off. If you do, you might want to forward them to the Postmaster so they can be examined first, some of the messages might be to your users but have the names misspelled or something. Then you can forward them to the correct person.
HTH
Ken