Exchange 2007 - Messages stuck in queue - 451 4.4.0

Posted on 2008-10-22
Last Modified: 2013-11-15
I've been configuring a Microsoft Exchange 2007 server and can currently send e-mail to most external domains. However, certain domains are rejecting e-mail with an error of:

 "451 4.4.0 Primary Target IP address responded with: "." Attempted failover to alternate host, but that did not succeed.  Either there are no alternate hosts, or delivery failed to alternate host".


 421-:  (DNS:NR)

I ran a DNS report and the "mail server greeting" section failed:

Failed Mailserver greeting - The server should have an A record which points to the mailserver for the hostname which is presented in the greeting:
   220 ****************************************************************************************

How can I change the A record so it points to the mail server for the hostname? Is that what is causing the messages to be stuck in the queue? I figured setting up an SPF record would remedy the problem but apparently it did not. Is there anything else I can try? I have a feeling reverse DNS may also have something to do with it. Help is appreciated!
Question by:qualityip
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Expert Comment

ID: 22778608
Is your outgoing mail server, or an example of a mail server you're trying to send mail to?  I'm guessing it's your outbound mail server; you may just need an A record that connects "" with an IP address.

Author Comment

ID: 22778841 is the outgoing mail server. What's the best way to go about getting/setting that host A record?

Expert Comment

ID: 22779130
I think I mis-spoke above, the record you will need is a reverse DNS record.  Normal DNS starts with a server name and provides an IP address; reverse DNS starts with an IP address and provides a name.  The record you need will be created by your Internet service provider, you may have to jump through some hoops to find support reps who know about reverse DNS.  The IP address for this record will be the external IP of your mail server.
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Author Comment

ID: 22779226
I called the ISP and they said Network Solutions is handling the primary DNS and Network Solutions said they do not offer PTR records with their DNS services. Is there anything else I can try besides switching the primary DNS to the ISP?

Accepted Solution

Scott1201 earned 500 total points
ID: 22780767
The primary DNS and reverse DNS would not be handled by the same company.  I've fought this battle before - the reverse DNS has to initiate with the ISP, because the resolution process starts from the IP address (owned by the ISP) rather than the name.  You should not need to move the primary DNS away from Network Solutions in order to get a reverse DNS record set up, but you might need to move up from first-level tech support at your ISP, or find a business support telephone number, before you run into someone who can help.

I do have clients who have reverse DNS through their ISP and primary DNS through Network Solutions or GoDaddy, so I know this can be done.

Author Comment

ID: 22787399
But of course, happens to be against AT&T policy to set up reverse DNS if they do not have the primary DNS. I really appreciate the help, any more suggestions?

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