Exchange 2010 - Help 451 4.4.0 DNS query failed


  • Hello.

    I am in the process of replacing our all in one exchange 2007 server with two cas servers and a mailbox server running exchange 2010

    I get this error when trying to send internal mail from exchange 2010 to exchange 2007.
    451 4.4.0 DNS query failed. SMTPSEND.DNS.NonexistentDomain.

    After a while the mails does get trough.

    I have tried disabling ipv6 in the registry as suggested elsewhere on this forum ( ), that made my internal network adapter register our internal network as an unknown (public) network, so i enabled it again.

    When sending the other way there is no problem. I have tried to send to a few external mails as well, and i havent experienced any problems there either, but since i only have a testuser running exchange 2010 i cant be sure the same error wont occur when sending to other external domains.

    Been at this for a few days, help is very much appriciated.
    Thursday, February 11, 2010 9:38 AM


All replies

  • Ok i read a little more, and noticed that adding ip to your host file could resolve this issue. i added the internal host name and ip of my 2007 server - and this does seem to work. i have now restarted the 2010 CAS server 5 times, and successfully send an e-mail after each reboot. I will continue to test, throughout the day to be sure,  and give you an update.

    That said, this seems like a dumb solution. Would be prefered to locate the source of this problem and fix it - now i might need to periodicly add ips to the host file, as i am not sure all external domains work.
    I'm not really sure how to do that... lets say i get the same error when sending to google, how would i go about adding that domain?
    do a mx lookup, notice - ping that, and add "" to my host file?
    Thursday, February 11, 2010 11:13 AM
  • Hi,

    That seems the known issue on the platform of Windows Server 2008 for the Exchange 2010, please refer to the below thread to workaround this issue:


    Tuesday, February 23, 2010 9:04 AM