Hi,
I have Edge server in DMZ and Hub in LAN.
today all messages (sent from outside) stuck in queue to hub server with message "451 4.4.0 DNS query failed".
I can normally connect hub server using ping or telnet 25 from edge server.
Messages from hub are sent to the outside correctly.
I have hub server address in hosts file entered.
I discover that the Edge server tries to get an IP address of Hub server from my ISP's DNS (I have set this address on network card):
2013-04-24T11:50:58.657Z,08D00EF8A2E5C3B3,SMTP,hub-server,>,DNS server returned ServerFailure reported by 194.204.159.1 2013-04-24T11:50:58.657Z,08D00EF8A2E5C3B3,SMTP,hub-server,-,Messages: 0 Bytes: 0 (The DNS query for 'SmartHostConnectorDelivery':'srv-ex1':'87939096-38c7-4517-8350-8936cf4220c5' failed with error : ServerFailure)
Why the edge server doesn't look for the hub-server IP address into hosts file first?
Temporary I changed the DNS settings on edge's NIC to my AD DNS and all messages was delivered correctly.