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Help with 451 4.4.0 Primary target IP address responded with: "421 4.2.1 Unable to connect.

Posted on 2009-12-17
Medium Priority
Last Modified: 2012-05-08

451 4.4.0 Primary target IP address responded with: "421 4.2.1 Unable to connect.  I have a scenario that I have old exchange 2003 server which is still using to send the email and the new exchange server 2007which has all the mail boxes.  I could not change it until I sorted out with Symantec mail security.

Mails are going to 99% domains but not going to very few domains and for these domains the above message coming.  If someone could help in this regard.

Could it be due to some SPAM black listing on these sites.  I have also check www.mxtoolbox for blacklisting and it does not mention any site which blocks our domain.
Question by:elaw
  • 4
LVL 83

Expert Comment

ID: 26076981
Hello elaw,

Try to resolve their MX from you Exchnage server.

Open command prompt and type :

nslookup -type=mx domainname.com

(where domainname.com is a domain for which you receive 421 4.2.1)

Compare the mx record (with mxtoolbox) and what you get from ping mx.domainname.com returned by you mail server nslookup to see if records match

LVL 13

Expert Comment

ID: 26077425
Hey ican help u but i am not at my desk so please wait r go to my profile and see answerd quetions thanks
LVL 13

Accepted Solution

NarendraG earned 1500 total points
ID: 26077532
Sending email to certian domains does not work when you run Exchange Server 2007 on a Windows Server 2008-based computer

You may have trouble sending mail to certain domains while using Exchange Server 2007 on Windows Server 2008. The Queue Viewer displays the following status error for the domain in question:

451 4.4.0 primary target IP address responded with 421.4.4.2 unable to connect.attempted failover to alternate host, but that did not succeed.Either there are no alternate hosts, or delivery failed to all alternate hosts.

This problem occurs because routers do not support the TCP autotuning settings in Windows Server 2008.

To disable autotuning, follow these steps:

Run CMD as Administrator

At the command prompt, type the following command, and then press ENTER:

netsh interface tcp set global autotuninglevel=disabled

This command disables the Receive Window Auto-Tuning feature.

Exit the Command Prompt window.

Restart the computer.
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LVL 13

Assisted Solution

NarendraG earned 1500 total points
ID: 26077537
try this also either one can you you

Can you run though this FAQ: http://www.it-eye.co.uk/faqs/readQuestion.php?qid=2

Thanks you
LVL 13

Expert Comment

ID: 26077541
r u using cisco pix router?

Author Closing Comment

ID: 31667611
Resolved the issue

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