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RESOLVED. In our case, it turned out our ISP had implemented some kind of DNS grey listing policy, in which DNS packets between [client IP, server IP] pairs were blocked unless there was a preceding attempt in the last 60 seconds. (see http://en.wiki...
So I'm on the other end - seems anyone with an Ironport has intermittent MX query failures to our domain Hitchcock.org.We've had a few critical partners set up SMTP routes to our mail servers, or as noted here have the Ironport query their internal D...
