We have Exchange 2010 Version: 14.03.0294.000 running on Server 2008 R2. Domain controllers are Server 2008 R2.
There are about 10 domain names that we get 451 4.4.0 DNS query failed. We send thousands of emails daily to many domains that go through fine. It started out with about four domain names, but now up to about 10. DNS, forwarders,
blacklists, etc., have all been verified and should not be a factor. I even contacted IT at a couple of these domains and they said we are not blocked in any way.
Using NSLOOKUP, when I set type=mx these domains will time out. If I use change to Server 8.8.8.8 then try again, I see the MX info. We recently upgraded our AV for F-Secure to Server Security 12. I stopped all F-Secure services on the Exchange server but still cannot get beyond DNS query failed for these domains. So I have ruled out the AV.
Servers have been rebooted, cache cleared, etc.
Any suggestions would be greatly appreciated.
Thanks.
DDaleS