Email bouncer Program(s) - know any?

Hi, I run PHP and mysql on my site. I allow people to use a PHP page to send me an email that is logged in the mysql for logging reasons. If someone sends me an email to whatever@mydomain.com (fake address, not real) when it is sent it does not bounce, instead it gets sent to the root email account. :( I don't want this as I don't read the root account all the time because emails that go there are mainly spam or from people who do not have the correct email address to send to. I don't reply to any in there. Just delete them, they take up space sitting there. Is there a Program(s) I can download or change a setting on my server to make them bounce back with a message? (like other web server do) Sure I could setup a autoresponder of some kind but I don't want to reveal the root account email. Can anyone help? Also I host other sites and domains, if I install a program on my web server for my emails to bounce will they work for them? Preferrably is there a program I can use to just use for my domain? And others can ask for it to be installed for their accounts. All help mostly appreciated. Thanks! http://search.yahoo.com.au - Yahoo! Search - Looking for more? Try the new Yahoo! Search