> Consequently I disabled the checks. Now, using spamhaus.org and spamcop > the > overload has disappeared.
Be careful with using the Spamcop blacklist to reject messages -- while it is perfectly fine as a blacklist to use in a scoring scheme such as SpamAssassin, I found it to have too many false positives to use it for outright blocking. If you use it for blocking, then you should consider complimenting your setup with a whitelist _on the MTA level_. -- Matthias