Someone is submitting fraudulent abuse complaints to SPAMCOP with our server's details. Everything checks out first to match with our server, but there are are some notable discrepancies which show that it is not indeed us. There's no match also in exim logs to these SPAM emails. For the record, our server only sends a handful emails per day.
We got a very good reason to believe that a competitor is behing this and is trying to get us out of business. There is one who has made open threats.
How do we stop these complaints from being submitted and find who is doing it?