Email blocklist · DNSBL · IP addresses MON · 14 SEP 2026

Spamhaus ZEN

Operated by The Spamhaus Project · United Kingdom · Zone zen.spamhaus.org

About

The de facto industry-standard IP blocklist. Used by the vast majority of mail servers worldwide as the first-line check. Free for personal and small commercial use; paid datafeed available for large operators.

Listing criteria

Composite list combining SBL (spam sources), CSS (snowshoe spammers), XBL (exploited hosts), and PBL (dynamic / end-user space). Listings are evidence-based, with removal procedures documented for each constituent list.

How to query

For an IP address 1.2.3.4, query reversed-octets-dot-zone:

dig +short 4.3.2.1.zen.spamhaus.org

A returned IP (such as 127.0.0.2) means listed. Each blocklist has its own set of return codes meaning different things; the operator's documentation explains theirs.

Operator site Delisting / lookup › Return codes ›