Hi,

We are having trouble to send to this one particular external domain. 

We received Delivery is delayed to these recipients or groups

Please advise what should i do?

Knizam,

send connector properties->Network->Check 'Use the external DNS Lookup settings on the Transport Server' if it is not checked already. Restart the transport service and see how it works

Hi, 

the 'Use the external DNS lookup' is checked. 

Also, i restarted the services and test send again, still DNS query failed.

What else can i check

Can you check with ISP? As all other domains are working fine, it can be on their end too..That's what I suggested in my last post to check ISP is fine

This is not a development question. I will move this to the mail flow forum on TechNet.

All other domain is working fine, except for this particular domain.

Then, i should contact both my DNS hosting company & the external domain about this issue.

At my side, is there anything can i double confirm the problem is not from my side?

thanks

Hi Knizam,

Any update?

Best regards,

DNS hosting company said there is no problem at their end.

The external domain still investigating and still haven't reply my query.

From my side, i perform SMTP test, does it affected the error ??

Hi Knizam,

Please refer to the following article :

451 4.4.0 DNS query failed Exchange Server error in message queue

To resolve this issue, fix the issues in your local DNS server, or configure the external DNS server for remote mail routing. To configure the external DNS server for remote mail routing, follow these steps:

1.Open the Proprieties page of the Exchange server that hosts the send connector, and then add the IP address of public DNS servers in the External DNS Lookups setting

2.Select the Use the external DNS lookup settings on servers with the transport roles option in the send connector that is responsible for remote mail routing.

Hope this helps,

Best regards,

Hi Niko Cheng,

TQVM.

The link resolved my problem.

451 4.4.0 DNS query failed Exchange Server error in message queue