Ben Kennedy writes:
mintier ben # host -t mx clients.sevenl.net Host clients.sevenl.net not found: 2(SERVFAIL) mintier ben # host -t a clients.sevenl.net clients.sevenl.net has address 208.92.235.137However when I do the same lookup from my office computer, I get reasonable results:Palladeon:~ ben$ host -t mx clients.sevenl.net clients.sevenl.net has no MX record Palladeon:~ ben$ host -t a clients.sevenl.net clients.sevenl.net has address 208.92.235.137 Presumably courier is rejecting messages because of the SERVFAIL.
Correct.
Does this demonstrate a problem with their DNS, or might I have some kind of problem on my machine? I feel I don't have a solid enough grasp of DNS (and courier's behaviour) to be sure.
This indicates a DNS resolution problem somewhere. DNS is distributed, and a failure anywhere in the resolution chain generally winds up as a SERVFAIL.
Generally, it may be a configuration problem; or it may indicate a transient network issue somewhere. If a forwarder has a referral, but cannot get a response from the authoritative server, it may respond back with a SERVFAIL until it does.
Trying this domain myself, I did get a SERVFAIL on the first query for the MX record, but a good NXDOMAIN for all subsequent queries. This does suggest a sporadic networking issue.
The only other thing that I see is that this domain has different NSes registered with the .net GTLD, then what the zone itself contains, but the IP addresses are the same. Still, it doesn't hurt to change the zone or the domain registration to have a consistent NS list for the domain, and this would be a cheap and quick way to see if that makes this glitch go away.
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