Spamhaus ZEN: The Survival Guide for Monetization Agencies

When you're managing high volumes of emails for partners or monetization campaigns, getting blacklisted by Spamhaus can quickly turn into a nightmare. In this article, we simply explain what the infamous ZEN list is, how to avoid it, and what to do if you're affected. This is an operational guide designed for email senders who want to maintain optimal deliverability.

• What is the Spamhaus ZEN list?
• How to check if your IP is listed?
• How to avoid being listed?
• You're blacklisted? What to do?
• In short: ZEN survival checklist for agencies

What is the Spamhaus ZEN list?

ZEN is a mega blacklist that combines several Spamhaus databases: SBL, XBL, PBL, and CSS. It blocks IP addresses considered risky by ISPs. If you send emails from an IP listed here, they'll end up in the spam folder (or be blocked outright).

• SBL: IPs suspected of spam activity
• XBL: IPs from compromised machines (trojans, worms, etc.)
• CSS: Low-reputation IPs sending too much suspicious volume
• PBL: End-user IPs (often dynamic) that should not send directly

How to check if your IP is listed?

You can quickly verify this on the Spamhaus site:

• https://www.spamhaus.org/lookup/
• Enter the IP address or domain you use for sending

You'll immediately know if you're listed, and in which sublist.

How to avoid being listed?

Here are the key best practices to adopt:

• Properly authenticate your emails: SPF, DKIM, and DMARC are essential.
• Use double opt-in: reduce the risk of dubious signups.
• Regularly clean your database: remove invalid or inactive addresses.
• Respect unsubscribe requests: make sure the links work and are processed.
• Monitor complaints: a high spam rate puts you directly at risk of blacklisting.

You're blacklisted? What to do?

Here are the steps to take immediately:

1. Stop sending: there's no point in continuing; messages are blocked.
2. Identify the cause: poorly targeted campaign, corrupted list, infected shared IP?
3. Fix the issue: apply the best practices listed above.
4. Request delisting on Spamhaus: clearly explain the actions you've taken.
5. Monitor your future campaigns: with a reputation testing tool or via Mindbaz.

In short: ZEN survival checklist for agencies

• ZEN = 4 blacklists in one, some very strict
• Listed IP = zero chance of reaching the inbox
• Monitor your reputation and only send with clean IPs
• Fix the problem before requesting delisting
• Train your teams or rely on a partner like Mindbaz

Want to secure your sender reputation? We’re here to support you every step of the way.