Posts tagged Exchange

Exchange: Email error 451 4.4.0 DNS query failed

After an upgrade of DC to 2012R2 and removing the old 2003 DC I found that Exchange had problems sending mail to a small amount of different domains. When I looked in the message queue I found that all these domains had the same error: 451 4.4.0 DNS Query Failed

Since I just had installed two new DC 2012R2 that now acted as the only DNS servers in the domain and that I recently read about extension mechanisms for DNS (EDNS) I figured this must be the issue. When EDNS is activated the DNS package can exceed 512 bytes and some firewalls don’t like this hence the DNS query failed problem.

But there is a quick fix for this and that is to just disable the EDNS on the DC:

  • At a command prompt, type the following command, and then press Enter:

    Note Type a 0 (zero) and not the letter “O” after “enableednsprobes” in this command.

    The following information appears:



Microsoft Exchange 2010 – EWS and big attachments


If you need to send big attachments with your MAC clients you need to change the default value for Microsoft Exchange 2010 which is set to 10MB/35MB (First release / SP1)

There are a few steps on how to get this to work, you need to change the file for your entire IIS environment, allowing the RequestFiltering to be changed and then change the actual value for  maxReceivedMessageSize and maxAllowedContentLength.



1. Change your file in “C:WindowsSystem32Inetsrvconfigapplicationhost.config” to allow requestFiltering override to Allow

2. Change your web.config located in “C:Program FilesMicrosoftExchange ServerV14ClientAccessexchwebews” to your new value. If you want to be able to send about 50MB attachments you should change the value to about 85MB as converting to MIME plays a part in this aswell. This value need to be changed on all your bindings that you are going to use, or just change them all to make it easy.

3. And then change your maxAllowedContentLength to the same value as above

4. Run the following command to make it stick after updates (Not sure if this really is needed but It wont hurt)

Start a cmd promt as admin and go to “%windir%system32inetsrv” and then run the following command:


5. Make a restart of your IIS and you should be up and running sending big attachments.


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