We have a problem with dns resolution of a mx record that causes mail to backup and eventually lead to a NDR.
From my investigation it is a result of our DNS server not responding with the requested information for a mx query.
today: from mail server to DNS1 server
request timed out.
A DNS request to our secondary dns server (DNS2) give us the requested information.
When i restart DNS on DNS1, the query gives us the same correct information and mail starts to flow. I am not sure what is causing this. Any thoughts?
We do not use forwarders, just root hints. Both DNS1 and DNS2 servers are configured identically as far as i can tell.
DNS1 is the primary server for all DNS for our environment.