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- URIBL http://www.uribl.com/ (rule URIBL_BLOCKED)
- DNSWL http://www.dnswl.org/ (rule RCVD_IN_DNSWL_BLOCKED). Note: Currently purposely sometimes returns wrong answers instead of a Block Notification
- Spamhaus http://www.spamhaus.org/ (various BLOCKED rules for different services)
- SURBL http://www.surbl.org/ (rule SURBL_BLOCKED)
- Validity http://www.validity.com (rule VALIDITY_BLOCKED)
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