[Exim] Blocking an a broken server

If you wanted to block all email from a broken exchange server that kept
sending out the same emails over and over again, but only a temporary
measure until it was fixed, what would be the quickest way to do it. I
have the helo name and the ip address.

/Ron
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Ron McKeating
Senior IT Services Specialist
Internet Services and Software Solutions
Loughborough University
01509 222329