I have my own domain, and a few email addresses on it, including a catch all address, with Google Apps. Recently, my catchall address has been receiving "delivery failure" emails from many different domains that are saying an email I tried to send to them was rejected or couldn't be delivered. But I didn't send any emails to these addresses. The original sender address is never a real email address I have set up. I have looked through my access logs, and no out-going emails were found from my address, and no emails to them in any outbox.
So I'm guessing someone is sending emails pretending to be me. So, can someone advise me as to what the implications are, and (if possible) what i can do to prevent it?