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.