What is Spamhaus (ZEN, DBL, etc.)?

If your emails suddenly stop reaching people, one of the first places to check is Spamhaus. They run the most widely used blocklists in the world, and a single listing there can cause widespread blocking across major mailbox providers, enterprise mail gateways, and hosting companies all at once.

Unlike smaller lists that cause scattered delivery failures, a Spamhaus listing hits hard and fast. That's why understanding which list you're on matters before you do anything else.

IP-based blocklists

• SBL (Spamhaus Blocklist) lists IP addresses of verified spam sources, known spam operations, and spam support services. These listings are investigated by humans, not automated.
• XBL (Exploits Blocklist) lists IPs of compromised machines: infected devices, open proxies, and hijacked systems used for spam delivery. If you're listed here, something on your network has likely been taken over.
• PBL (Policy Blocklist) lists IP ranges that aren't supposed to send email directly to the internet (residential IPs, dynamic ranges). This isn't a punishment. It's Spamhaus saying those IPs should route through their ISP's mail servers instead of sending directly.
• CSS (Combined Spam Sources) is an automatically generated list targeting low-reputation IPs, particularly ones used in snowshoe spam (where senders spread sending across many IPs to avoid detection).
• ZEN combines SBL, XBL, PBL, and CSS into one zone. Most organizations query ZEN rather than checking each list individually, so ZEN is the one that matters most day to day.

Domain-based blocklists

• DBL (Domain Blocklist) lists domains used in phishing, malware distribution, and spam. Your domain can land here even if your sending IP is perfectly clean, which catches a lot of senders off guard.

How to check your status

Go to check.spamhaus.org and look up your IP or domain. It takes about 30 seconds. You can also run a quick check with our free blocklist checker if you want to scan across multiple lists at once.

Getting delisted

Each list has a different removal process, so don't treat them all the same.

• SBL requires contacting Spamhaus directly and showing you've identified and resolved the problem that caused the listing.
• XBL removals are largely automated once the security issue (compromised device, open proxy, etc.) is actually fixed.
• PBL removal means either working with your network provider or demonstrating that you legitimately operate a mail server from that IP range.
• DBL requires addressing the underlying domain reputation issue first, then submitting a removal request.

Still if you're dealing with a Spamhaus listing right now and not sure where to start, our SOS hotline is free and we can help you figure out which list you're actually on and what the next move looks like.