Spamhaus ZEN Explainer
ZEN is the combined zone most mailbox providers query. Each sub-list (SBL, XBL, PBL) gets you blocked for different reasons.
What: Manually-listed IPs of known spam sources. Used by ~90% of major MBPs.
Cause: A human Spamhaus volunteer determined your IP is the source of spam.
Removal: Fix the underlying cause (compromised account, list problem) and apply via Spamhaus removal form. Usually delisted within 24-48h if cause is fixed.
What: Automated detection of compromised hosts and known botnet IPs.
Cause: Your IP was seen sending spam from a botnet, or your server is open-relay / proxy-abusable.
Removal: Close the compromise (patch, reset credentials, audit relay config), then auto-delisting starts within hours of clean behavior.
What: IPs that should not be sending mail to begin with. residential, dynamic, dial-up ranges.
Cause: Your IP is in a range your ISP told Spamhaus shouldn't be a mail sender.
Removal: You can self-remove from PBL if you have permission from your ISP to send mail. Or: switch to a static/business IP range.
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See your numberExplains SBL (manually-listed spam sources), XBL (automated detections / botnets), PBL (policy block. IPs that shouldn't send mail), and the removal process for each.
After a Spamhaus listing. Before assuming your deliverability problem is something else.
FAQ
What's the difference between SBL, XBL, and PBL?+
SBL is a manual listing by a Spamhaus analyst who decided your IP is a spam source. XBL is automated detection of compromised or botnet hosts. PBL is a policy listing that says this IP range was never supposed to send mail at all, like residential or dynamic addresses.
Does this page look up my IP on Spamhaus?+
No. It explains what each sub-list means and how removal works for each one. The actual lookup and the removal request both happen on Spamhaus's own site.
How fast does delisting happen?+
It depends on the list and on whether you fixed the cause. XBL tends to clear within hours once the compromise is closed, SBL removals are usually processed within a day or two after you apply, and PBL can be self-removed if your ISP permits you to send mail.
Keep going
Articles, glossary entries, and other tools on the same topic.
Nate built Outsolvi after watching every email-tracking tool he had ever used lie to him about opens. Outsolvi grades every open as a person or a machine, in Outlook and Gmail, so the number on the dashboard is one a rep can actually act on.
We update these pages when the underlying mechanics change. new mailbox-provider rules, new tracker behavior, new measurement gaps. The dates above are real revisions, not auto-touches.