How Does the MTA Know That Lack of an A Response Is Not a Temporary DNS Lookup Failure?
Last updated on NOVEMBER 15, 2017
Applies to:Oracle Communications Messaging Server - Version 6.0.0 and later
Information in this document applies to any platform.
In one deployment, administrators had placed the NOMX keyword on channels, which tells the MTA not to use MX DNS records. At a later time, they then removed related A records from DNS, leaving the MTA with no DNS records it could then rely on for routing.
While this was clearly a configuration misstep that was easily rectified, this may lead us to question how the MTA knows whether the lack of a DNS A record response is a temporary lookup failure or not.
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