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DNS Query Failed on single record

Joseph_Barron
on
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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?

Joe
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