How Does the MTA Know That Lack of a Response Is Not a Temporary DNS Lookup Failure? (Doc ID 2230476.1)

Last updated on APRIL 07, 2022

Applies to:

Goal

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. 

Solution

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