[Exim] reject recipient at relay host?

Hi!

we are relaying mail for another server.
we are getting lots of mail for a certain email address which doesn't exist
(:blackhole:) on the target server. Is there a way to reject emails for
that address at SMTP time? The emails keep sitting in our mailq, since the
target host is responding with:
451 Cannot check..... at this time - please try later

Thanks!

Philipp