Hi,
I had a couple of other posts open for issues with mailflow during AD upgrade, but thought this needed a new post.
Essentially we have a single domain in a single forest. Three sites (main office and two remote offices), the main site containing 2 x 2008R2 AD servers, 2 x MSX2007 servers (Primary and SCR Target) and 2 x MSX2013 servers in a DAG. The remote sites each
contain a 2008R2 DC only.
This has been in place for probably a year (slowly slowly migrating) and seems to work reasonably well. We were decommissioning some old AD servers and at around this time I noticed mail flow issues, mainly from 2013 to everywhere else.
I've made entries in the MSX2013 hosts files for each others IP addresses, and created a new receive connector on one of the MSX2007 servers for Exchange Authentication so that both MSX2007 machines can talk Exchange Auth.
This has fixed most of the problems, but from time to time one of the MSX2013 servers shows the queue with a next hop domain of 'Site:Default-first-site-name' begin retrying with the last error of"451 4.4.0 DNS query failed. The error was: DNS query failed with error InfoNoRecords"
The queue will contain messages from people on MSX2013 mailboxes to people with MSX2007 mailboxes.
Usually after 15 minutes, the queue empties and the messages send.
I see solutions such a using smarthosts for the affected domains (eg. if mail gets like this when sending to gmail.com) but I am not sure what I would do for an AD site.
Does anyone know what might cause this or where I could check for more information?
Thanks