Who operates the major blocklists?

Major blocklist operators include: Spamhaus (most influential globally), Barracuda Networks (BRBL), Invaluement (URI-focused), SURBL (link-based), Spamcop (complaint-driven), and various regional operators. Each maintains independent databases with different listing criteria.

Spamhaus operates multiple lists: SBL (known spam sources), XBL (exploited systems), PBL (policy block list for dynamic IPs), and DBL (domain blocklist). Being listed on Spamhaus affects delivery broadly due to widespread use.

Other significant operators: URIBL (link checking), Composite Blocking List (CBL, part of Spamhaus XBL), and MBP-specific lists maintained internally by Gmail, Microsoft, etc. Different blocklists serve different filtering systems; comprehensive monitoring checks multiple sources.