SpamCop FAQ : SpamCop Mail Service : FAQ about Filtering and Held Mail :
Sometimes people are wondering why a particular email gets held. Here, I will try and teach you how to discover that on your own.

Look at the full headers of the message

At the bottom of the headers, Spamcop adds it's own stuff. The headers we care about here are X-SpamCop-Checked and X-SpamCop-Disposition

• The LAST IP in the X-SpamCop-Checked list is the one that resulted in the message being held
• If the X-SpamCop-Disposition says "Blocked bl.spamcop.net" then proceed, otherwise you will need to refer to the website for the blocklist (see the bottom of this page for some multi-search pages)
• go to http://spamcop.net/bl.shtml and enter the LAST IP from the list into the lookup box
• from there, you will see information about why that server is blacklisted.

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Here are a few URLs where you can look an IP up in many lists at once, which is sometimes more indiciative of a server's real behaviour than just testing one blocklist.

• http://www.dnsstuff.com/
• http://www.openrbl.org/ (seems busy and uses javascript and etc, but it does have a few things such as google searches of news.admin.net-abuse.* )