I have a client who's been getting these bounce-backs to his email. I've tried to use the exchange message tracker, but the bounced messsages don't show up. I'm guessing that someone who associates with him has a spammer virus that is using the addresses in their mailbox as return addresses for spam. I have a copy of one of the bounces, and I see some interesting data, but I don't know what to do with it. Can someone tell me if there is anything in this that I could use to track down this spammer? The user and company name have been changed for privacy.