The Spamhaus Project

ZEN Blocklist

About the Data

ZEN is the combination of all Spamhaus' free IP-based DNSBLs into one single powerful and comprehensive blocklist to make querying faster and simpler. It contains the SBL, CSS, XBL, and PBL blocklists. Please see the pages (also listed below) dedicated to each component list for individual policy descriptors.

Benefits of this data

For efficient, fast querying, users can utilize the ZEN dataset. Please note, if you are using ZEN, in most configurations there is no need, or additional benefit, to also query other Spamhaus IP blocklists. This will result in extra queries, already covered by ZEN, and unnecessary infrastructure usage.

Email administrators can apply this DNSBL to reduce the overflow of inbound email traffic associated with spam and other malicious emails. This will reduce risk of security incidents, reduce email infrastructure costs, and reduce human resource requirements.

Fun fact: this blocklist was named after Spamhaus' founder, Steve Linford's German Shepherd, Zen. For many years, Zen faithfully guarded the Spamhaus base in England. From the great kennel in the sky, Zen lives on to help guard your networks, customers and the Internet at large.

What’s included in ZEN?

Each blocklist targets a specific type of behavior. Using one blocklist independently limits the effectiveness of the data - using ZEN as a comprehensive dataset helps to secure the best email protection available. The blocklists covered through ZEN are:

Due to its IP nature, ZEN does not provide any protection against malicious or suspicious domains. So to gain the best catch rates, domain and hash blocklists should also be used to filter email, once the email has been accepted. Spamhaus provides the Domain Blocklist (DBL) for free. Find more on why you should use domain and hash blocklists here.

Technical information

A DNS query to the ZEN DNSBL generally results in several distinct answers within the same DNS response packet, one for each dataset where the IP is listed. The answers have a different return code for each dataset, and therefore the information obtained from ZEN is the same that would be obtained from separate queries to the SBL, CSS, XBL and PBL DNSBLs, but using less resources.

You can utilize the data via the SMTP server configuration for connection and SMTP transaction checks, and via open source tools, such as SpamAssassin and Rspamd, for content analysis.

Plugins for both are readily available to minimize configuration time, for users of Spamhaus Technology's free Data Query Service.

Alternatively, integrate with your existing anti-spam platforms with technical information to support here. Set up takes minutes and you instantly gain real time protection.

Accessing the data for free

Use of the Spamhaus DNSBLs is free of charge for low-volume, non-commercial users. If you’re unsure, please check our DNSBL usage criteria. Free accounts are made available through our partner, Spamhaus Technology - sign up to access the data via Data Query Service.

Where data is being used for commercial purposes, an annual subscription-based service is required. Sign up for a free 30-day trial.

Best practices to maintain a positive IP reputation

Spamhaus’ data protects billions of mailboxes globally. To avoid getting listed and your email service being impacted, some important best practices are:

  1. Restrict outbound SMTP traffic - configure your firewall to allow outbound SMTP traffic (destination port 25) only if originated from your mail server internal IP (if you have one).
  2. Infrastructure - check your internet infrastructure providers, e.g. ISPs. See reputation statistics on ISPs/networks.
  3. Use double opt-in – to avoid spam traps and ensure only real and interested recipients are sent your emails.
  4. Configuration – ensure that your hostname and your HELO match, and that your reverse DNS (PTR record) is defined and pointing to the same hostname.

For more specifics, see visit the individual blocklist pages as above.

N.B. We recognize these are not all managed by email administrators; where applicable, communicating with other functions, like network administrators and deliverability specialists, is critical.


If your IP is listed on the ZEN blocklist, you’ll also see a corresponding listing to one of the following blocklists: SBL, CSS, XBL or PBL. Visit which will take you to our IP and Domain Reputation Checker, to understand more detail, with steps on how to remediate.

Other Blocklists Available From Spamhaus


Combined Spam Sources

Learn more


Domain Blocklist

Learn more


Exploits Blocklist

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Policy Blocklist

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Spamhaus Blocklist

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PBL, SBL & XBL combines

Learn more