DNS server can find A records but not MX?

Posted on 2006-07-19
Last Modified: 2011-09-20
I have 12 DCs all running DNS.  My mail gateway is using one in particular for DNS and lately we've been getting a few of these

The following message to <> was undeliverable.
The reason for the problem:
5.4.7 - Delivery expired (message too old) 'DNS Soft Error looking up (MX) while asking 192.168.75.x. Error was: ServFail'

so i tested looking up that MX record from that DC and it times out.  When I look it up from all the other DCs in the domain it finds it fine.  Also when I look up just the A record for it finds it fine.  The only difference in configuration is that this DC has forwarders on (pointed to our ISPs DNS servers).  I took them off to see if that would make a difference but it still fails.  I've run dcdiag and netdiag and both come back clean.

any ideas what else could be going on?
Question by:shanna1017
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Expert Comment

ID: 17139358
I would check to make sure the DNS forwarders are still correct.  Your DNS server shouldn't know about so it will have to go to the ISP's DNS servers to get an answer.

You mentioned that your other DNS servers don't have forwarders setup, are you hosting the "." zone?  If so I suggest deleting it and handling all of those requests from your ISPs DNS.

Author Comment

ID: 17139380
thanks for the quick reply.

i've used nslookup to lookup that address using those ISP DNS servers and it finds the MX record fine.  The other DNS servers are simply using root hints to find domains other than ours.  Is that what you're asking?
LVL 22

Expert Comment

ID: 17139398
OK, you are just using root hints.  I wanted to make sure you didn't have a forward lookup zone called "."  If you are you should delete it.

I know this seems silly, but have you tried restarting DNS services on the server or restarting the whole server?

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Author Comment

ID: 17139405
i've tried restarting the DNS service on that server but not the whole server since it's our main file/print server.  I will try that tonight

Author Comment

ID: 17139722
actually i found a time when nobody had open files and quickly rebooted it.  still can't find the MX record.  

i don't get it?  what could be stopping it?  it's not in our domain so it should just use the forwarders to query the ISPs DNS servers right?  and those have already proven that they know about that record.  


Expert Comment

ID: 17140608
did this only start happening this afternoon?

Author Comment

ID: 17140928
i think i actually fixed it by disabling Extension Mechanisms for DNS.  After I did that and restarted the service I was able to retrieve the MX record from that box.  either that or it was just coincidence.  Anybody have any explanation for why that would fix it?  The only reason I'm suspicious is because we only have 1 internet connection that all traffic from our WAN goes through so if that fixed the issue why would the other servers have been able to do it successfully with that feature turned on?

Accepted Solution

ee_ai_construct earned 0 total points
ID: 17545632
PAQ / Refund
ee ai construct, community support moderator

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