ORB UK Open Relay Block Zone (ORBZ) Manual
The ORBZ is a manually generated blocklist (or blacklist) of IP addresses identified as open SMTP relays used to distribute unsolicited email.
Updated on 17 Jun 2026: We updated this guide to correct ORBZ history and add clearer steps for open-relay delisting and repeat-listing prevention.
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Check if you are listed on ORB UK Open Relay Block Zone (ORBZ) Manual
And 143 other blocklists.
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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 is ORB UK Open Relay Block Zone (ORBZ) Manual?
The ORB UK Open Relay Block Zone (ORBZ) Manual is a manually generated blocklist (or blacklist) of IP addresses associated with servers believed to be open SMTP relays. An open relay accepts email from an unauthenticated sender and forwards it to third-party recipients, which lets spammers route unsolicited mail through someone else's mail server.
ORB UK's policy is to publicize these open servers as one cause of unsolicited commercial email (UCE). ORB UK does not directly block email. It publishes a DNS-based blocklist (DNSBL), and receiving mail systems query that DNSBL during connection or message handling. If the sending IP address is listed, the recipient's mail server can reject the message or apply a local filtering rule.
The list is narrow in purpose. It is about open relay behavior, not sender reputation, content quality, DMARC alignment, or whether a domain is legitimate. Treat a listing as a mail server configuration problem first.
Who runs ORB UK Open Relay Block Zone (ORBZ) Manual?
ORB UK is the organization associated with the Open Relay Block Zone (ORBZ) manual blacklist. ORBZ was operated as a Basingstoke, England, volunteer-run open-relay DNSBL, with Paul Cummins identified at the time as the person running ORBZ. Alan Brown is tied to the earlier open-relay project that preceded ORBZ, so ORBZ is better described as a successor to that work rather than Brown's original project.
How to prevent relisting
Removal is only durable when the mail server no longer relays third-party mail for unauthenticated users. After the relay is closed, keep the server under normal outbound controls so the same IP address is not listed again.
- Disable unauthenticated relaying for external senders and external recipients unless the connection is explicitly trusted.
- Require SMTP AUTH for remote users and limit relay rights to known networks and authenticated users.
- Review mail logs for relay attempts, rejected relay traffic, sudden outbound volume, and old application hosts after changing the MTA configuration.
- Keep SPF, DKIM, and DMARC records accurate so authentication troubleshooting does not hide a relay problem.
- Use Suped's DMARC reporting to separate domain authentication failures from blocklist or blacklist symptoms, while treating ORBZ removal as a mail server configuration task.
How to get removed from ORB UK Open Relay Block Zone (ORBZ) Manual
If you are the postmaster or system administrator for a listed server, request removal only after the server is closed as an open relay. Delisting requests fail when the server still accepts unauthenticated third-party relay traffic. Threats or legal pressure do not fix the underlying test result.
- Close the open relay first. Check your MTA relay rules, trusted networks, application credentials, and any legacy host exemptions.
- Send the delisting request to removal@orbz.gst-group.co.uk after remediation, and include the listed IP address plus the changes made to stop relay abuse.
- Expect ORB UK to retest the server. If the server no longer relays unauthenticated mail, the listing is removed. If it still relays, it stays listed.
If the server becomes an open relay again, it is relisted quickly. Keep the fix documented so future mail server changes do not reopen relay access.
What's the impact of being listed on ORB UK Open Relay Block Zone (ORBZ) Manual?
The impact of being listed on ORB UK Open Relay Block Zone (ORBZ) Manual is generally low because this historical, narrow open-relay DNSBL is not a common default dependency for major mailbox providers. That does not make the listing harmless. Any receiving mail server that still uses this blocklist can reject mail from the listed IP address or route it into stricter filtering.
For troubleshooting, separate two issues: the IP-level listing and the domain's authentication. Fix the open relay for ORBZ delisting, then review SPF, DKIM, and DMARC alignment for the domain so legitimate mail is easier to identify. Suped's DMARC reporting can help with the authentication side of that workflow, but it does not replace closing the relay.
