Spamhaus Project
Spamhaus ZEN
Aggregate of Spamhaus SBL, XBL, and PBL — the single most consulted IP blocklist in email.
- DNS zone
zen.spamhaus.org- Target
- IP addresses
- Severity
- high
What it lists
ZEN combines Spamhaus's SBL (verified spam sources), XBL (exploited hosts and proxies), and PBL (end-user IP ranges that should not deliver mail directly). A ZEN listing is the most consequential blacklist hit in email — most major mailbox providers and many filtering appliances query it for every inbound message.
Who gets listed
Spamhaus lists IPs with confirmed spam emission, snowshoe behaviour, hijacked netblocks (DROP/EDROP), open proxies, and dynamic ranges that should be sending via an authenticated relay.
Reputation impact
Severe. Major providers (Gmail, Microsoft 365, Yahoo, Apple) treat a Spamhaus ZEN listing as strong evidence to reject or quarantine. Plan for partial-to-total delivery loss while listed.
How to delist
Look up the IP at check.spamhaus.org, identify which sub-list (SBL, XBL, PBL) is matching, fix the root cause (compromised host, missing rDNS, dynamic IP, etc.), and request delisting through the form linked next to the listing.
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