How to refuse mail if there’s no mailbox

Can I tell Exchange that if there’s no mailbox, don’t accept the e-mail? For example, if mail is sent to mailbox1@domain.com, and there is no mailbox1, I don’t want it floating around for 2 more days. I see junk mail in the Q from people who’s accounts were deleted over a year ago.

Thanks.
I’m running EX2k SP1 – single server Ex Organization.