The problem isn't that the enroute computer has been labeled as a spammer... it's that it's been labeled as "having an open relay." This means that there's a security hole on that computer that hackers can exploit -- and MAY have exploited before.

The complaint MAY not have come from Spancop, since manually doing complaints (as many of the oldstyle gripers do) would have forwarded the note about the open relay to RBLS (the Black Hole list, which is NOT maintained by Spamcop). It can also come via other routes (since hackers spider for open relays, some of the big spam blocking companies ALSO spider for open relays.) Our mail system where I work got into the RBLS because we did, indeed, have an open relay.

We weren't spamcopped. It was caught by a spider and reported.

...trying to explain it to the folks who set up the internet connections ...took quite a bit of time. Many ISPs are actually unaware of this security issue and are unaware that they have problems until someone reports it.

So yes, ISPs do get blocked. They need to know about it so they can patch the security hole and then reappy to the RBLS folks to be taken off the list (this is what we did.) RBLS will then spider you and if your security drops, you can end up on their RBLS list again.

But this isn't Spamcop's doing. It's the keepers of the RBLS list which many firewalls use to block spammers.