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Tried this here but no luck<br />
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<a href="http://exchangeserverpro.com/messages-queuing-error-451-4-4-0-dns-query-failed/" rel="ugc">http://exchangeserverpro.com/messages-queuing-error-451-4-4-0-dns-query-failed/</a>
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Tried this here but no luck

http://exchangeserverpro.com/messages-queuing-error-451-4-4-0-dns-query-failed/ [http://exchangeserverpro.com/messages-queuing-error-451-4-4-0-dns-query-failed/]

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I have an SBS 2011 not sending emails. I had other issues this morning with an open question here <a href="https://www.experts-exchange.com/questions/28654833/URGENT-SBS-2011-in-reboot-loop-from-Windows-Updates.html" rel="ugc nofollow">https://www.experts-exchange.com/questions/28654833/URGENT-SBS-2011-in-reboot-loop-from-Windows-Updates.html</a><br />
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Now none of the emails are going out. In the Exchange Management Console queue viewer I have this error &quot;451 4.4.0 DNS query failed&quot;. It keeps on retrying but no luck.<br />
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I use the ISP SMTP server for sending emails. I can telnet the SMTP server no problem. It does not appear to be an DNS issue.
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I have an SBS 2011 not sending emails. I had other issues this morning with an open question here http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/SBS_Small_Business_Server/Q_28654833.html

Now none of the emails are going out. In the Exchange Management Console queue viewer I have this error "451 4.4.0 DNS query failed". It keeps on retrying but no luck.

I use the ISP SMTP server for sending emails. I can telnet the SMTP server no problem. It does not appear to be an DNS issue.

SBS 2011 not sending emails

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Small Business Server (SBS) is a line of server operating systems targeted at small businesses by bundling the operating system with a number of other Microsoft products that would normally need to be purchased or licensed separately. The most notable inclusions are Exchange, SQL Server, SharePoint and ISA/TMG (Microsoft's firewall and proxy server).

The Domain Name System (DNS) is a hierarchical, globally distributed system responsible for associating the name of a computer, service or other resource into an IP address for connecting to the Internet or a private network. Most prominently, it translates domain names to the numerical IP addresses needed for the purpose of computer services and devices worldwide.