Best Tips to Fix Exchange Server Error 451 4.4.0 DNS Query Failed

Curious in knowing the resolution of 451 4.4.0 DNS query failed error in Exchange? Do you know, just like you, there are numerous users who are encountering the same issue? Yes, this problem associated with Exchange Server getting a huge attention due to the increasing queries of users. All of them have the same question that how to resolve Exchange Server Error “451 4.4.0 DNS query failed?

Consider this query of a user:

“For me working with Exchange is always been a great experience. However, two days back I got an error while accessing the database displaying “451 4.4.0 DNS query failed error.” I have no idea why I was getting the error and then tried every possible method to bring Exchange back to working mode. I have searched for some manual solutions, but none of them proves helpful to me. Now, I am eagerly looking for an application or any other trick to fix this error as soon as possible. Please help me out for the same.”

This Error of Exchange is related with the device failing DNS lookup because of the misconfiguration of the address blocked by recipient domain manually. Users can perform few steps of reconfiguration and check the connection to resolve it. They can use utilities such as NSLOOKUP and TELNET for examining the working of Edge transport layer, which controls outbound or inbound exchange of the email messages. However, sometimes these tools fail to fix the issue. In such situations, the need for a third party tool to fix Exchange Server Error 451 4.4.0 DNS query failed in Exchange 2010, 2013 or 2016. We will come to this, but before that let us discuss some more facts about the error.

Symptoms of Exchange Server Error 451 4.4.0 DNS Query Failed

• Not able to send emails to a certain domain.
• 451 4.4.0 DNS query Failed Error.

Identification

The trouble with inbox/outbox emails getting stuck or not getting delivered. The problem is generally, encountered by Microsoft Exchange 2007 edition with Edge Transport Role installed. This is related to email queues belong to edge transport layer.

Methods to Fix Error 451 4.4.0 DNS Query Failed

Configure the DNS Setting once again on Edge Transport layer

Examining Queue Viewer:

• First, open EMC on Edge Transport Server.
• Now, go to toolbox>>Queue Viewer.
• Find Mail flow tools>> Queue Viewer tool.
• Then, verify the column of last error for any inbound email messages from any accepted domains encountering same problems or not.

Analyzing DNS Configuration on Edge Transport Server

• It is necessary to log in on the Edge Transport server locally. If you are accessing the physical server remotely via RDC 6.0 then it is recommended to run “/console” switch.
• Now, open Exchange Management Console>>Edge Transport Server>>Properties.
• Select Internal DNS lookups, you need to set default configuration as All Available.

Executing Internal & External DNS Lookups

Internal Lookup:

Those users, who have various networks adapters installed, go to the internal network card, then choose that card for DNS Settings of Network Card.

• With this step, all the available IP addresses gets populated and you can change if there is any misconfiguration
• Initialize Transport Service once more and confirm Exchange Management Console>>Edge Transport Server>>Properties to verify the accurate configuration.
• If no IP addresses are detectable, it indicates that NIC might not be configured with the entries of DNS server. Fill the card with appropriate details and examine transport server properties once again to confirm the accurate configuration.

External Lookup:

Those users who have a single network card with public DNS, modifying configuration may affect external name resolution & might limit the flow of email. In this case, you have to choose Use these DNS and select IP of internal DNS. After this, add host file consisting DNS information. In the final step, verify the correctness of configuration.

Analyzing DNS Servers & Name Resolution

Once we check the DNS Servers configuration, now it is required to check that whether they are executing appropriate DNS name resolution or not. 25 ports are used to send SMTP/ outbound emails that in this situation creating the problem of the queue because of inappropriate DNS name resolution. Use NSLOOKUP to test the port.

Using NSLOOKUP Tool

NSLOOKUP is a network administration command line tool, which is used to obtain DNS records holding server & IP address information.

Locating IP Address of the Server

• First, use cmd, type in “nslookup” and hit Enter. It will open NSLOOKUP tool
• Now, type set type=mx and then hit on Enter
• After this, type set timeout=20, because by default we have the limit of 15 seconds to carry out DNS query.
  Then, you need to enter the domain name for which you wish to take out the MX record and then, hit Enter.

Checking SMTP Connection via TELNET

• First, use cmd and type; telnet to begin its services.
• Now, enter set logfile (location:/filename).
• Then, type open mail1.google.com 25 & press Enter.
• You need to type EHLO contoso.com and hit Enter.
• Use parameters like MAIL From, RCPT TO, Notify, Data, & Subject for creating a test message.
• Finally, the report will be generated as per the success of configuration. It could be success report or failure report.

If telnet services indicate failure then verify that if Windows Firewall is turned on or not. If it is not, then configure it on NIC cards for permitting services like SMTP, testing protocols like ICMP, and LDAP ports.

Alternate Solution

If all your efforts fail to rectify Exchange Server 2010 451 4.4.0 DNS query failed error then, you can take the help of third party tool, which ensures a guaranteed solution. The name of the software is Exchange Server Recovery Software. It is designed to repair Exchange database as this may be the cause of this error. The tool is capable enough that users can depend on this utility and fix the error without any trouble.

The Bottom Line

Microsoft Exchange is one of the major platforms that is used to meet the requirements of the business. However, errors like 451 4.4.0 DNS query failed in Exchange 2016, 2013 or 2010 creates hurdles in between the work. Considering this, we have come up with some manual strategies to rectify this issue. If not resolved manually, users can go to a trouble free method as discussed.