How to Set Up a Connector to Reroute Mail to an Internal Domain in Office 365

How to Set Up a Connector to Reroute Mail to an Internal Domain in Office 365


 

Managing email routing efficiently is crucial for organizations that use Office 365 (Microsoft 365). If you need to reroute emails to an internal mail server (such as on-premises Exchange or a third-party system), setting up a mail flow connector is essential.

In this guide, we will walk you through the step-by-step process of creating a connector in Office 365 to reroute emails to an internal domain.

Prerequisites

Before setting up the connector, ensure you have:

  • Administrator Access: You must have the necessary admin privileges in Exchange Online.
  • Internal Mail Server Details: The IP address or FQDN of your internal mail server.
  • TLS Certificate (Optional but Recommended): If using a secure connection, ensure your mail server has a valid TLS certificate.

Step 1: Access the Exchange Admin Center (EAC)

  1. Sign in to Microsoft 365 Admin Center.
  2. Navigate to Exchange Admin Center (EAC) by going to Admin centers > Exchange.
  3. Click on Mail Flow from the left panel.
  4. Select Connectors.

Step 2: Create a New Connector

  1. Click on the + Add a Connector button.
  2. In the wizard that opens, select:
    • Connection Type: Choose From Office 365.
    • To: Select Your organization's email server.
  3. Click Next.

Step 3: Configure Connector Settings

Name and Description

  1. Give your connector a meaningful name (e.g., "Reroute Mail to Internal Domain").
  2. Add a description for future reference.
  3. Click Next.

Routing Options

  1. Choose how you want to route emails:
    • Use the domain name system (DNS) to route mail (if your mail server has a public MX record).
    • Route email through a smart host (enter the IP address or FQDN of your internal mail server).
  2. Click Next.

Security Settings

  1. TLS Settings:
    • If your internal mail server supports TLS, select Always use TLS.
    • Choose whether to validate the certificate.
  2. Domain Restrictions:
    • Enter the specific domains for which this connector should apply (e.g., internaldomain.com).
  3. Click Next.

Step 4: Validate and Save the Connector

  1. Validation Test:
    • Enter a test email address that belongs to your internal domain.
    • Click Validate to ensure mail flow is working.
  2. If the validation passes, click Save.

Step 5: Verify Mail Flow

After setting up the connector, send test emails to verify that mail is rerouting as expected. You can:

  • Check message headers in Outlook to confirm the routing.
  • Review the mail flow logs in Exchange Admin Center.
  • Use the Message Trace tool to track email movement.

Troubleshooting Tips

  • Ensure the internal mail server is reachable from Office 365.
  • Check firewall rules to allow SMTP traffic.
  • Verify TLS certificate validity if using secure routing.
  • Review the Exchange Online Protection (EOP) settings to prevent filtering issues.


Conclusion

Setting up a mail flow connector in Office 365 helps reroute emails efficiently to an internal domain. By following these steps, you can ensure a seamless email flow between Office 365 and your internal mail server.

If you have any questions or face issues, drop a comment below!

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