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Exchange 2010 error 451 4.4.0 DNS Query Failed

Posted on 2010-09-08
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Last Modified: 2012-10-23
Hello I am having problems sending to a couple domains. We have recently upgraded to an exchange 2010 server and everything was working fine. I was able to send email to example1.com with out any issues and all of a sudden we can not. The messages get stuck in the queue with error 451 4.4.0 DNS Query Failed. Can some help shed some light on this error?

Thanks
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Question by:Holguer
9 Comments
 
LVL 6

Expert Comment

by:Dustin99352
ID: 33632750
Is the server using two NICs or something?  It's possible you could be querying a different DNS server then you suspect.  Make sure that your exchange environment is querying your Domain Controller and not some external DNS or something.

Thanks
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LVL 32

Expert Comment

by:endital1097
ID: 33632755
try your basic nslookup test
nslookup
set type=mx
example2.com

verify that dns is locating the mx record for the domain

do your windows dns servers use your isp dns servers as forwarders?
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Author Comment

by:Holguer
ID: 33632779
It only has one nic card set with the internal dns
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Author Comment

by:Holguer
ID: 33632787
I just reran the nslookup to example2.com see the proper mx records. DNS appears to be working
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Assisted Solution

by:Holguer
Holguer earned 0 total points
ID: 33632802
Yes the ISP dns is set as forwards in the DNS server settings
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LVL 4

Expert Comment

by:milikad
ID: 33634211
Try to create exclusive Send Connectors for the domains to which server is failing to
send mail to and add the MX Records’ IP Addresse as the Smart Host for respective
domains on the Send Connectors and check if you are able to send mails.
MILIKAD

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LVL 4

Expert Comment

by:milikad
ID: 33634229
To support the earlier comment check the below link
http://support.microsoft.com/kb/972744 
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Accepted Solution

by:
Holguer earned 0 total points
ID: 33785419
The issues was resolved by the following:
Under oraganization configuration , hub transport, send connector, properties, networks, check Use the External DNS Lookup on the transport server.
Then under Server Configuration, hub transport, server properties check the radio button Use these DNS servers: Add your external DNS servers
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Expert Comment

by:eweber-UST
ID: 38204342
Thank you,
@Holguer

I added my ISP's external DNS servers and it work. I looked in the Queue viewer and I dont see any emails.

Thank you,

E
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