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DNS Query Failed on single record

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Last Modified: 2012-05-12
We are running Windows 2008 SBS Standard, which has been up for about 3 years. Email is flowing with the occasional hicup. On Monday a customer upgraded to Microsoft Office 365 and now hosts there email at Microsoft. Emails to that address are getting a delayed delivery message back to the user with the Last Error of:

451 4.4.0 DNS query failed.

I have tried:
    - Testing the nslookup and it is returnning the A record fine.
    - Have Flushed the DNS    ipconfig /flushdns
    - Cleared the DNS cache
    - Tested the SMTP server from MXtoolbox and it is working although giving the warning:
         Warning - Reverse DNS does not match SMTP Banner
    - Even added a mx record to my local DNS zone for the domain.

Any thing else to try?

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Top Expert 2011

   - Testing the nslookup and it is returnning the A record fine.
Did you lookup the A records of the MX records?

Can you telnet to the receiving servers MX from your mail server?

Also it might be worth trying the same from another messaging system like gmail for instance as the issue may not be isolated to you.

Do you have any admin control over the recipients DNS or messaging i.e. is it something you support?


This is email coming from an outside company, so I have little or no control. They claim that they are getting all other email and gmail and other accounts seem to work.

Additional tests:
I sent email from two other clients running Microsoft Exchange 2007. Company A has SBS 2008 Standard and Company B has Exchange 2007 Enterprise (much larger company). Company A failed and Company B went through. So it seems that there is an issue with Two small business server installations that I did.

Additional Information
Apparently, when the company we are sending the email switched to Microsoft Office 365, they left some of the DNS stuff from the other provider and have been told to remove that information before additional testing can be done. So that may be the cause. But it will take a bit of time for it to propogate.
Top Expert 2011
What is the MX server you are having trouble resolving so I can check their DNS records in regards to your additional information?




In Queue Viewer for Microosoft Exchange 2007, I am seeing a strange message when trying to send to one domain. It is reporting the Last Error:

"452 4.3.1 Insufficient System Resources".

Other domains are flowing properly. The email is only 17KB in size. I see nothing in my event log.

Is this message coming from my server or the recipiant's server?


When switching to Microsoft Office 360 Email they setup the DNS entries incorrectly.

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