I have child domain DC/GC/Exchange server which does not seem to be replicating with my root domain server. Users on this site cannot send emails to users on a new child domain exchange server which was installed a month ago. One of the errors I get when doing replication tests from the server in question: ******* 70 CONSECUTIVE FAILURES since 2012-03-22 15:16:20 Last error: 8524 (0x214c): The DSA operation is unable to proceed because of a DNS lookup failure. Please help...

So you have the root domain in one site and the child domain in another site? And users in the root (parent) domain cannot send email to recipients in the child domain? What about users in the child domain? Can they send email to the parent domain? Are you familiar with the dcdiag and repadmin tools? If so, I would run those (dcdiag is easy enough, in its most basic use, you just type "dcdiag" at the command line - without quotes - and press enter). Can you tell if the domain controller(s) in the parent domain can resolve the names of the domain controllers in the child domain? Are there any other errors in the Event Logs concerning DNS?Please mark as helpful if you find my contribution useful or as an answer if it does answer your question. That will encourage me - and others - to take time out to help you.

Hi, Please try to perform a DCdiag command to narrow down the issue. dcdiag /test:dns /s:DCname /DnsBasic After that, I recommend you to post the issue in forum for Windows Server to solve the DC related problem. http://social.technet.microsoft.com/Forums/hu/winserverDS/threads More related information to share with you: Event ID 2087: DNS lookup failure caused replication to fail http://technet.microsoft.com/en-us/library/cc785014(v=ws.10).aspxXiu Zhang TechNet Community Support