We have an Exchange server behind an ISA server and it is the address of the ISA box that is blacklisted.
Causes of listing
System has sent mail to SpamCop spam traps in the past week (spam traps are secret, no reports or evidence are provided by SpamCop)
SpamCop users have reported system as a source of spam less than 10 times in the past week
Additional potential problems
(these factors do not directly result in spamcop listing)
DNS error: 188.8.131.52 has no reverse dns
Part of our network is used by computers we have no control over and I suspect one or more of them has a virus. I cannot block SMTP for everything except our mail server because many of these machines mail out directly using SMTP / POP3.
What I am looking for is any help you could offer in tracking down the offending machine(s)