Forum Discussion

MCT

Mar 06, 2024

Solved

Exchange 2016 hybrid queue stuck

Hello I recently run a Hybrid wizard everything good! the only thing that I have is a problem in the communication between on prem accounts and exchange online . when I send a message to a mi...

LeonPavesic
Mar 07, 2024
Hi José Leonardo Ovalles Jimenez,

the error 451 4.4.0 DNS query failed typically occurs when there’s an issue with the DNS servers or the communication between your on-premises accounts and Exchange Online.
Here are a few steps you can try:
Establish Send Connectors for Affected Remote Domains:
This problem may occur if remote DNS servers disregard AAAA queries or provide unexpected responses. To address this, create send connectors for affected remote domains and configure them to utilize the remote domain's email server as a smart host.
Verify DNS Server Functionality:
Ensure the DNS server used by Microsoft Exchange Server is functional. Exchange Server typically utilizes the DNS settings of the network adapter for outgoing remote email routing. Resolve any issues with the local DNS server or configure the external DNS server for remote email routing.

Configure External DNS Server for Remote Email Routing:
Open the properties page of the Exchange Server hosting the send connector and add the IP address of public DNS servers in the "External DNS lookups" setting. Select the option "Use external DNS lookup settings on servers with transport roles" in the send connector responsible for remote email routing.
451 4.4.0 DNS-Abfrage fehlgeschlagen Exchange Server Fehler in der Nachrichtenwarteschlange - Exchange | Microsoft Learn

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Kindest regards,

Leon Pavesic
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LeonPavesic

Silver Contributor

Mar 07, 2024

Hi José Leonardo Ovalles Jimenez,

the error 451 4.4.0 DNS query failed typically occurs when there’s an issue with the DNS servers or the communication between your on-premises accounts and Exchange Online.
Here are a few steps you can try:

Establish Send Connectors for Affected Remote Domains:
This problem may occur if remote DNS servers disregard AAAA queries or provide unexpected responses. To address this, create send connectors for affected remote domains and configure them to utilize the remote domain's email server as a smart host.
Verify DNS Server Functionality:
Ensure the DNS server used by Microsoft Exchange Server is functional. Exchange Server typically utilizes the DNS settings of the network adapter for outgoing remote email routing. Resolve any issues with the local DNS server or configure the external DNS server for remote email routing.
Configure External DNS Server for Remote Email Routing:
Open the properties page of the Exchange Server hosting the send connector and add the IP address of public DNS servers in the "External DNS lookups" setting. Select the option "Use external DNS lookup settings on servers with transport roles" in the send connector responsible for remote email routing.

451 4.4.0 DNS-Abfrage fehlgeschlagen Exchange Server Fehler in der Nachrichtenwarteschlange - Exchange | Microsoft Learn

Please click Mark as Best Response & Like if my post helped you to solve your issue.
This will help others to find the correct solution easily. It also closes the item.

If the post was useful in other ways, please consider giving it Like.

Kindest regards,

Leon Pavesic
(LinkedIn)
(Twitter)

José Leonardo Ovalles Jimenez

MCT

Mar 08, 2024

Thanks LeonPavesic

It was done througth de first option:

Establish Send Connectors for Affected Remote Domains:
This problem may occur if remote DNS servers disregard AAAA queries or provide unexpected responses. To address this, create send connectors for affected remote domains and configure them to utilize the remote domain's email server as a smart host.