[Exim] Returned mail

I am running EXIM and have just 1 tiny problem. I'm an ISP and some
of my users run a maillist (PHP / PERL). When they are using their
maillist and some emails could't be sent to the emailadress. I get
those emails in my mailbox (root).

Is there a way to avoid this? Because it is quite anoying.

Sincerly N. Elsten