External DNS lookups in Exchange Servers

In an Exchange environment (Exchange 2013 or higher), it is recommended to configure the DNS servers that Exchange uses for DNS  name resolution. Generally,
I always recommend configuring DNS servers for external and internal lookups to avoid delays in email delivery due to DNS lookup issues or unresolvable names.

To configure external DNS lookups in Exchange 2013 or higher versions (in Exchange Admin Center), navigate to " Servers ," highlight the server you wish to configure, and then click the Edit button.


Navigate to "DNS lookups " select the network adapter in the External DNS lookups section.

Once you select the correct network adapter, you will see your internal DNS servers listed in the following screenshot. Navigate to " DNS lookups" select the network adapter in the External DNS lookups section.

Click on plus button to add DNS servers



In an Exchange 2013 or higher versions, it is recommended to configure the DNS servers that Exchange uses for internal name resolution. Generally, Exchange server NIC will be configured with internal DNS servers as below. And it is supposed to be like this.



Be careful when configuring Exchange Server 2013 or higher versions in this manner, and make sure you test the changes afterwards to ensure mail flow is still functioning correctly. Misconfigured DNS settings can cause problems with the Exchange server, such as emails stuck in the queue.


Hope it helps.