Hi Guys,
I was facing a problem in sending mails using Exchange 2007. In queue viewer I could see the 451 4.4.0 DNS Query failed error. After spending some time on google to solve this problem; I have followed the steps mentioned below;
Setup: behind firewall, windows 2003 standard edition server and Exchange 2007.
I am not using any smart host to send the mail.
1. Check that the Send Connector (Organization Configuration -> Hub Transport -> Send Connectors) created as "Internet" in Intended type of usage.
2. In Organization Configuration -> Hub Transport -> Send Connectors, right click on the created send connector;
=> Go To the "Network" tab.
=> 1. There "Use domain name system (DNS) "MX" record to route mail automatically" should be selected;
2. Keep "Enable Domain Security (Mutual Auth TLS)" unchecked.
3. Check "Use the External DNS lookup settings on transport server"
3. Go to the Server Configuration -> Hub Transport
=> Right click on exchange server -> properties
=> click on "External DNS Lookups"
=> click on "Use these DNS Servers"
=> Here, add internal as well as your ISPs DNS.
=> If "Use these DNS Server" is already clicked; check the added DNS IPs and confirm that added DNSs are reachable. (PING those DNS IPs)
4. Also make sure if you are behind the firewall; 53 port is opened for DNS Lookups.
5. I have also executed command "dnscmd /Config /EnableEDnsProbes 0" on command prompt.
Many Thanks to
This may solve your problem.
Have a nice Time..
