My company has got a valid email address firstname.lastname@example.org. Somehow it seems like the email address is used by spammers to send out spam emails. Whenever we check the inbox, we'll get tons of "Undeliverable:Your e-mail could not be delivered" to email addresses that we have never seen before, and we never send emails to those email addresses.
I have run a check of our IP on the major blacklists and the results were clean. We are using exchange server 2003, is there anything that I can do to stop people from using our email address to send spam emails?