I have a mailflow-issue that is giving me trouble.
We have an SBS2008 which we are trying to migrate to Exchange 2010 running on Windows 2008 R2. The new machine is set up, I migrated one test-user over.
Mail flows from 2010 to 2007, but not the other way.
I've had this often with 2003 <-> 2010, but never in this constellation.
All receive connectors have Exchange Server authentication active. Additional send connectors have been removed. All looks well.
Mail is stuck in the queue of 2007 with the error message "451 4.4.0 DNS query failed. The error was: SMTPSEND.DNS.NonExistentDomain; nonexistent domain"
Both receiving and sending user are in the same mail domain. Their addresses are correct. It works the other way.
The "next hop domain" in queue sais "hub version 14" - something I have never seen.
What is wrong?