What are the major email blocklists (e.g., Spamhaus, Spamcop, Barracuda, SORBS)?

Several blocklists have significant impact on email deliverability. The most influential is Spamhaus, which operates multiple lists: SBL (Spamhaus Block List) for known spam sources, XBL (Exploits Block List) for compromised systems, and PBL (Policy Block List) for IPs that should not send mail directly.

SpamCop focuses on user-reported spam and provides a real-time blocklist that many organizations consult. Barracuda Reputation Block List (BRBL) is widely used by organizations running Barracuda security products.

SORBS (Spam and Open Relay Blocking System) maintains lists based on various criteria including open relays and dynamic IP ranges. URIBL and SURBL specifically list domains found in spam message content rather than sending IPs.

Not all blocklists carry equal weight. A Spamhaus listing has severe impact because major providers consult it. Lesser-known lists may have limited effect.

Know which harbors check which registries. Spamhaus is the one list you cannot afford to ignore.