How to Set Up DNS Routing in Exchange 2013 or later

This process begins with configuring outbound filtering policy, described in Step 1 below. You must perform Step 1 regardless of whether you have already configured your outbound email to send through the SmartHost. 

The steps in this article address the following situation:

An email addressed to multiple recipients fails for a single recipient, but Exchange generates a Non-Delivery Report (NDR) reporting that the email failed to send to all recipients.

These steps explain how to set up DNS Routing in Exchange 2013+. This will force your Exchange server to break up an email sent to multiple recipients within different domains into separate emails, while still sending it to Email Gateway Defense for outbound filtering.

Step 1. Configure Outbound Filtering Policy

Follow the instructions to configure Email Gateway Defense to accept email from your mail server for outbound filtering. See Step 2 - Configure Email Gateway Defense for Exchange 2013 and Newer for details.

Step 2. Configure Exchange to use Barracuda Networks for External DNS Lookups

1. Log into ECP – https://<webmail.yourdomain.com>/ECP replacing webmail.yourdomain.com with the FQDN of your mail server.
2. From the left navigation panel, click Servers.
3. Make sure Servers is selected at the top, and click the pencil icon to edit the properties. You must to do this for each server listed here.
4. In the left navigation panel of the new window, click DNS Lookups.
5. For External DNS lookups, select Custom Settings, as shown here, and add the IP addresses provided in How to Configure DNS Routing for Improved Performance.
   
6. Click Save.
7. In the left navigation panel, select Mail Flow, then Send Connectors.
8. Click the Plus icon to create a new send connector. Enter the following information:
   1. Name: Outbound to Barracuda
   2. Type: Partner
      
9. Click Next.
   1. Select MX record associated with recipient domain.
   2. Select the Use the external DNS lookup settings on servers with transport roles box.
      
      
10. Click Next.
    1. Click the Plus icon and type an asterisk for the domain.
       
       
11. Click Next.
    1. Click the Plus icon and add your source server(s).
       
       

12. Click Finish.
    
    

    Note: If you previously created a send connector earlier in Step 2 - Configure Email Gateway Defense for Exchange 2013 and Newer, delete it now. Your system will now use the new send connector you created in Step 1 above.

Step 3. Verify Mail is Flowing

1. Log into Email Gateway Defense.

2. In the Dashboard page, verify inbound and outbound messages are being logged for the selected domain.

   You can also click Message Log to view inbound and outbound email traffic. Use the filters to refine your search.