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Wednesday, August 07, 2013, 14:59

Why am I seeing the error "Deferred: Name server: host name lookup failure"?

Category: Troubleshooting

Solution ID: 00000214

Summary:

Why am I seeing the error "Deferred: Name server: host name lookup failure" on messages stuck in the mail queue?

Answer:

This error message occurs when PerfectMail is unable to resolve the domain name of the sending e-mail address in DNS. Most often this occurs when spammers make up ficticious domain names when sending spam.

However, in rare circumstances this can also signal a problem with your local DNS resolution. DNS resolution is required for e-mail analysis and delivery, so there may be a problem affecting your e-mail flow. To see the validation error report go to the "Reports > Server Status" page and look at all of the validation results. There will be lines for each DNS server saying "Querying DNS server" with the results.

Try the following:
1) Reboot your local DNS Server
2) Restart your MTA using the PerfectMail Dashboard

After restarting these services go to the web administrator interface "Tools > DNS Lookup" page. Enter the IP address of the questionable DNS server and lookup names for domains that you would not normally see. The idea is to try and find domain names that would nor normally be cached on your DNS server.

Sometimes we see DNS servers misbehave when performing new lookups. When this happens DNS lookups for cached entries appear to work fine, but new lookups appear to fail. Restarting DNS services appears to fix this problem in the short term.


Tags: DNS, warning, resolution, server, failure, configuration

Link to this article: http://perfectmail.com/kb/deferred_host_name_lookup_failure

Updated: Wednesday, August 07, 2013, 14:59

-- David Rutherford

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Last modified: 2017-11-29, 10:04

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