Key takeaways
- The Spamhaus Project’s fair use policy prohibits DNS queries from resolvers or servers without attributable reverse DNS - this includes Korea Telecom’s infrastructure.
- To signal that the free Public Mirrors are no longer providing protection, queries from Korea Telecom will return the error code 127.255.255.254.
- If your mail server does not handle this error code correctly, it may reject all emails.
- To maintain seamless email filtering, migrate to the free Data Query Service. Sign up here.
- Configuration changes are simple and quick - see our technical documentation for details.
Why are Korea Telecom users affected?
The free Public Mirrors are designed for small-scale, non-commercial use. The Spamhaus Project monitors usage according to its fair use policy to ensure fair access and a high-quality service. However, Korea Telecom’s default reverse DNS setup prevents The Spamhaus Project from attributing queries to individual organizations. This makes it impossible to determine whether usage falls within acceptable limits, necessitating a block on queries originating from Korea Telecom.
Why move to the FREE Data Query Service?
DQS offers several advantages over the free Public Mirrors:
- Transparent usage – Register for FREE and receive a key that tracks query volume.
- Improved performance – Blocklists are updated in real-time, ensuring the latest threat intelligence.
- Expanded protection – Access additional blocklists, including: Zero Reputation Domain Blocklist, Domain Blocklist with Hostnames, and Auth Blocklist.
Steps to access the free DQS
- Remove all legacy Spamhaus Project DNSBL configurations before signing up to ensure you receive your verification email.
- Sign up for a DQS account.
- Verify your email address.
- Log in to your account and retrieve your DQS key.
- Update your email configuration using our guides for mainstream MTAs.
When will Korea Telecom queries be blocked?
The block will be introduced gradually, from Wednesday, September 17th, 2025.
What if I don’t want to use the free DQS?
Alternatively, you can use a DNS resolver with an attributable reverse DNS to continue to be protected for free by The Spamhaus Project’s DNSBLs. If you choose not to continue using The Spamhaus Project’s DNSBLs, you’ll need to remove all related configurations from your email infrastructure
Need more information?
Learn more about Spamhaus Project’s DNSBL return codes.
- Read previous announcements from The Spamhaus Project: Using our public mirrors? Check your return codes now.
- For more help: Contact us via Twitter @spamhaustech, LinkedIn @Spamhaus-Technology-ltd, or our contact form.