Minor problem with bounced mail.

I'm bouncing mail from over-quota users. Not a big deal except when I
need to bounce back to someone that gave their username as <> or the
their is an invalid reply address, is there any way to just discard
these mail messages? I have someone who is apparently on someones
binaries mailing list and is also away. His mailbox fills up, then it
starts filling up my queue. I can't complain to the user because it
is an invalid address and looks like a mailing list anyway. I've sent
a message off to the injection point but that is strangely silent.

Roger