451 4.4.0 DNS query failed after P2V, Exchange 2010
So, the P2V conversion completed successfully on our Exchange 2010 server. I brought the virtual machine into full production Friday night and everything looked great. First thing Monday morning I get a call from our CLO that mail is being delayed and not reaching external mail recipients. I did a quick Google search and discovered that this would happen in Exchange 2007 and it was a bug, but we’re running 2010. I finally figured out what the issue was and I kicked myself.
My solution was to open EMC and go to Server Configuration -> Hub Transport. Right-click on your server’s name and open Properties. Make sure that External DNS Lookups and Internal DNS Lookups both have valid entries. Our entries were blank since the network hardware changed. As soon as I corrected these and clicked OK, mail started flowing outbound again!