[Exim] Disabling Mail delivery failed errors

Hi,

Is there an option I can set which will disable Mail delivery failed:
returning message to sender messages; I use Exim on my webserver with a
bulletin board running, and users with Hotmail addresses that are over quota
being sent mail about replies to their postings get bounced back to me, to
the point where I'm receiving 30 of them an hour.

Failing an option, how would I go about routing the messages to /dev/null?

Cheers,

Scott Pettit