ORB UK Open Relay Block Zone (ORBZ) Inputs
ORBZ is a public blocklist (or blacklist) of IP addresses identified as open SMTP relays often used to send unsolicited bulk email.
Updated on 17 Jun 2026: We updated this ORBZ guide to separate ORBZ from ORBS and add practical DNSBL remediation steps.
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Check if you are listed on ORB UK Open Relay Block Zone (ORBZ) Inputs
And 143 other blocklists.
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abuse.ro
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Team Cymru
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ZapBL
2stepback.dk
Fayntic Services
ORB UK
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TechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftWhat are ORB UK Open Relay Block Zone (ORBZ) Inputs?
The ORB UK Open Relay Block Zone (ORBZ) Inputs list is a legacy DNSBL-style blocklist (blacklist) for IP addresses that have tested as open SMTP relays. An open relay accepts mail from one outside party and forwards it to another outside party without proper authorization, which lets spammers hide the original source and push traffic through someone else's mail server. ORBZ itself does not block email. Receiving mail servers decide how to use the DNSBL result in their own SMTP policy.
When a message arrives at a receiver that still references this blacklist, the receiver checks the connecting IP address against the ORBZ zone. A positive result means the server has been reported or tested as an open relay. Depending on the receiver's policy, that result can lead to a temporary rejection, permanent rejection, quarantine, or extra scoring in a spam filter. The correct fix is to close the relay and then request retesting or delisting.
Who ran ORBZ?
ORBZ is best understood as a historical successor to Alan Brown's Open Relay Behavior-modification System (ORBS), not the same project. Contemporary reporting from 2001 described ORBZ as the Basingstoke, England Open Relay Block Zone operated by Paul Cummins on a voluntary basis after ORBS closed. The current page name uses ORB UK, but old references also appear as ORBZ or Open Relay Block Zone.
Some older ORBZ text described the list as 'Fair Comment in the public interest' and named contributors to the scripts that ran the service. For operational work today, treat a bounce message naming ORBZ as the primary evidence that a receiver still queries this blocklist or a cached copy.
How ORBZ DNSBL checks work
ORBZ works like a DNS-based blacklist. A receiver reverses the octets of the connecting IPv4 address and queries the ORBZ zone. Listed IPs commonly return an A record, and TXT data can provide a reason shown in SMTP logs or bounce messages.
DNSBL lookup patterntext
Sending IP: 192.0.2.10 Query name: 10.2.0.192.<orbz-zone> Positive result: receiver applies its local reject, quarantine, or scoring policy
The rejection code is controlled by the receiving system, not ORBZ. A 451-style temporary SMTP response tells the sender to retry later, while a 550 or 553-style response usually creates an immediate bounce. This distinction matters when you read mail logs during delisting.
How do I get removed and delisted from ORBZ?
Start with the mail server, not the listing request. ORBZ-style open relay blacklists list the IP because the host accepted third-party relay traffic, so a removal request without a configuration fix usually fails or results in relisting.
- Lock down SMTP relay rules so unauthenticated users cannot send to external recipients through the server.
- Require SMTP authentication for submission, keep port 25 restricted to server-to-server mail, and verify trusted IP ranges are narrow.
- Review mail logs for third-party relay attempts, compromised accounts, and unexpected outbound spikes before requesting delisting.
- Email removal@orbz.gst-group.co.uk to request retesting if that mailbox still accepts requests. Include the listed IP, the fix applied, and the date the open relay was closed.
- Wait for retesting. If the service confirms the server is closed, the IP should be removed; if it remains open, the IP stays on the blacklist (blocklist).
If that contact path no longer works, use the bounce message to identify the receiver using ORBZ and ask that receiver which DNSBL zone or cached blacklist result triggered the rejection. The underlying fix is still to close the open relay.
What's the impact of being listed on ORBZ?
The practical impact is low for most modern senders because ORBZ is a legacy open-relay DNSBL with limited visible adoption today. A listing still matters when a recipient's mail server, gateway, or custom SMTP policy queries ORBZ, because that receiver can reject or defer your mail during the SMTP transaction.
Expect issues to be receiver-specific rather than domain-wide. Check SMTP logs and bounce text for the exact blocklist or blacklist name, the rejected IP address, and the SMTP response code. If you use Suped's DMARC reporting, compare the rejected IP against known sending sources for your domain before changing mail flow; the ORBZ delisting action still depends on fixing the server.
