What happens if a DNSBL Server does not respond?

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Question

What happens if my server can’t do a lookup on the DNSBL server either due to DNS being unavailable or the DNSBL Server being offline?

Answer

If the DNSBL Server is unavailable for whatever reason, SMTP continues working and continues to transfer mail as if no RBL had been set.

However, if the DNSBL server first accepts a connection from your server and then fails to respond, the DNSBL Server time out will apply. The timeout is not configurable and is set to 30 seconds.

If you are affected by this then you should do one of the following:

  • Contact the owner of the DNSBL service and find out why it is not responding correctly;
  • Remove the offending DNSBL Server from your list; or
  • Continue with the timeout delays.

The performance of remote DNSBL servers is completely outside of the control of GMS software.

See Also:

Keywords:respond response hang DNSBL

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