Help with open DNS resolver

Pietro Leone

• February 16, 2026 13:56
• Edited

Hello,

i got some false positives from spamcop. Looking in cpanel documentation i found:

Important:

If you use a open DNS resolver (such as Google®, CloudFlare® or OpenDNS®), Spamhaus and other public DNSBL servers may return a "not listed" (NXDOMAIN) message. Your system will fail to properly mark the site as a source of spam. If you use any blacklist in WHM’s Exim Configuration Manager interface, we recommend that you use your hosting provider’s or network provider’s resolvers. If you must use an open DNS resolver, be aware that this issue may occur.

i am using powedns , it does not provide a recursive (caching) nameserver. (requires external nameservers in resolv.conf) 

what is the best option ? go back to bind? install recursive powerdns and start use 127.0.0.1 ? what does cpanel recommend?

currently i am using provider resorver and google for backups

thanks

 

• 

  cPRex Jurassic Moderator

  • February 17, 2026 14:37

  Hey there!  What IP addresses do you have configured in /etc/resolv.conf on your system?  That is likely the root cause of this issue so let's starts by checking that file.

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• 

  Pietro Leone

  • March 04, 2026 18:00

  8.8.8.8 and 8.8.4.4 It Is Google DNS

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• 

  cPRex Jurassic Moderator

  • March 05, 2026 04:29

  That's going to be the issue right there - you'll want to speak with your host to see if they can provide you with resolvers you can use in that file.

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  Pietro Leone

  • March 09, 2026 15:10
  • Edited

  [root@virgo ~]# cat /etc/resolv.conf
  ; generated by /usr/sbin/dhclient-script
  nameserver 213.186.33.99 (myprovider)
  nameserver 8.8.8.8 (google)
  nameserver 8.8.4.4 (google)

  using "Whitelist: IP addresses that should not be checked against RBLs [?]" wih major provider IPs in list i have mitigated the problem, but it still persist.

  also i got warning from csf RBL check:

  cbl.abuseat.org

  Error: open resolver; https://check.spamhaus.org/returnc/pub/51.38.xxx.xxx/

   

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• 

  cPRex Jurassic Moderator

  • March 09, 2026 13:34

  Does everything work as expected if you comment out the two Google lines?

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  Pietro Leone

  • March 09, 2026 15:11
  • Edited

  removing google i still got warning in CSF:

  cbl.abuseat.org

  Error: open resolver; https://check.spamhaus.org/returnc/pub/51.38.xxx.xxx/

   

  spamcop is not triggered because i have whitelist major provider IPs

   

  maybe also OVH dns resolver is considered open DNS  ?!? 

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  cPRex Jurassic Moderator

  • March 10, 2026 14:56

  I'm honestly not sure, but if they are specifically flagging that 51.38.x.x IP address then that could be the case that is experiencing an issue somehow.

  It would be best to reach out to your host to see if they are aware of any issues with that DNS resolver.

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