How to Configure External DNS Servers on an Outbound SMTP Virtual Server
When you configure external DNS servers, you specify a different DNS server than the server that is configured in the TCP/IP properties of the computer running Exchange Server. This DNS server is used by SMTP to resolve external DNS names and deliver mail.
Before You Begin
Before you perform the procedure in this topic, read Verifying DNS Design and Configuration.
How to configure external DNS servers on an outbound SMTP virtual server
Click Start, point to All Programs, point to Microsoft Exchange, and then click System Manager.
In the console tree, expand Servers, expand <Server Name>, expand Protocols, and then expand SMTP.
Right-click <Your Outgoing SMTP Virtual Server>, and then click Properties.
Click the Delivery tab, and then click Advanced. The Advanced Delivery dialog box appears.
The Advanced Delivery dialog box
In Advanced Delivery, click Configure. The Configure dialog box appears.
The Configure dialog box
In Configure, click Add, type the IP address of the external DNS server that you want to use, and then click OK.
In Configure, under External DNS, verify that the IP address is correct, and then click OK twice to apply the settings.