SURBL (Spam URI Realtime Blocklist) evaluates URLs inside email messages rather than sender IP addresses. It operates as five distinct sub-lists targeting phishing, malware, cracked sites, abuse patterns, and a combined multi-list. Legitimate senders can get listed without sending spam — through hacked CMS installs, affiliate links with bad reputation history, insecure contact forms, or linking to newly registered domains. Warning signs include SMTP 554 bounce codes on clean IPs, unexplained click-through rate drops, and complaint spikes tied to specific URLs. Removal requires identifying and fully fixing the root cause before submitting a detailed request to surbl.org. Prevention involves auditing all links in email templates, using dedicated sending domains, and avoiding links to domains registered within 72 hours.
