SURBL

What it means

SURBL describes itself as specialising in reputation data provided in near real-time feeds, used to secure mail flow, SMS, web access and DNS firewalls. Its publicly provided Multi data set lists domains of malicious or abused websites and can be used to filter or tag messages by the links in their body, regardless of sender IP. It complements lists of bad sending IPs.

SURBL's open letter to redirector operators describes spammers using redirection sites to wash the destination of their links, which is why shared redirect and shortener domains can end up listed.

For senders, the practical risk is a listed domain in the body (a tracking domain, a shortener, an image host or a compromised site) rather than the sending domain itself.