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.
Explains 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.
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You know the rule. See where you sit against it.
Reference pages tell you the benchmark. Outsolvi tells you whether your team is above or below it — per-rep, per-deal, per-week — and which behavior changes move the number. From $7/user/mo yearly.
See your numberNate built Outsolvi after watching every email-tracking tool he had ever used lie to him about opens. Outsolvi runs Tier 1 to 5 confidence scoring on every open, native 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.