"451 4.4.0 DNS query failed" error in Edge Transport RRS feed

  • 問題

  • We are using Exchange 2007 SP1. The topology is:

    - 2 x mailbox servers running in CCR at internal network.
    - 1 x Hub Transport + CAS at internal network
    - 1 x Edge Transport at DMZ

    Yesterday, we found that emails sending to two domains (say a.com and b.com) were queued up in the Edge Transport with error "451 4.4.0 DNS query failed". I checked the "send connector" and it uses "External DNS" to resolve domain names. I then checked the "External DNS" definition in both Edge and Hub Transport and found that the DNS entries were set correctly (which is pointing to our ISP's DNSs).

    With our AD, we have DNS, too. However, it is for internal use only. Within this internal DNS, we have both a.com and b.com zone records defined but there is no MX record in them.

    Strangely, after removing the zone records in our internal DNS, the pending emails can send out. After all the pending emails were gone, we rebooted the Edge Transport and add back the zone records of a.com and b.com to our internal DNS. After that, emails sent to these two domains could go through without problem.

    This is really a strange case. Does anybody come across this? Any reason for this issue?


    Joseph Liu
    2009年5月8日 上午 02:40


  • Hi Joseph TK Liu,


    I want to confirm the following information with you:


    1.       How did you add DNS zone (a.com and b.com), please send the screenshot of them to v-rocwan@microsoft.com for analyze.

    2.       Did you subscribe your Edge Transport server to internal Active Directory site?

    3.       Open the Exchange Management Console on the EDGE server,

    4.       Select the EDGE server in the TOP, MIDDLE pane, and select properties, click ExternalDNS Lookup, send the screenshot of it to me.

    5.       How many NICs do you have on Edge transport server?


    Exchange 2007 SP1 also includes a parameter in the EdgeTransport.exe.config application configuration file that is named DnsFaultTolerance. This parameter has the following values:


    Lenient (default setting)  



    6.       Send the EdgeTransport.exe.config file to me.


    Related articles:


    Configuring Transport Server Properties



    Send Connector Properties > Network Tab



    Rock Wang

    Rock Wang– MSFT
    2009年5月8日 上午 07:30