How are SURBLs different from SpamHaus SBL?
SpamHaus’ SBL contains IP addresses of blacklisted web servers, name servers, and mail senders. SBL can be used to check message senders and message bodies, but using SBL to check message bodies requires resolving the domain names found there into IP addresses. However the act of resolving the domain can confirm for senders of unsolicited messages that your specific address was reachable, that you’ve opened their message, etc. And the name resolution can significantly delay the amount of time it takes for your provider’s servers to process each message. (The delay is on the order of a few seconds to a few minutes; not a big deal to an end user, but a major bottleneck to the provider’s servers which typically need to handle thousands of messages much more quickly.) In contrast, SURBLs contain mostly domain names that have appeared in message body URIs. Typically those are the web sites that are being advertised. Using SURBLs doesn’t require resolving the domains that appear in messages.
