You can't stop it. Just delete the bounces and be done with it.
Possibly if the virus's are also being sent to you, and the 'Received' host is consistent, you could possible know someone who is using that ISP. Mail daemon bounces sometimes reply with the supposed senders header so you can check it out there as well.
-- Simon Males <[EMAIL PROTECTED]> No More AOL CDs Australia - www.anticd.org -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
