Scenario: Conditional mail routing in Exchange Online

There might be times you need to route mail differently depending on who the mail is sent to or from, where it's being sent, the contents of the message, and so on. For example, if you have multiple sites around the world, you might want to route mail to a specific site. You can do this using connectors and mail flow rules (also known as transport rules).

When the steps below are completed, a mail flow rule will redirect messages addressed to users whose City property is set to New Orleans to the IP address specified by the Outbound connector.

Step 1: Use the Exchange admin center to create the connector

The first thing we need to do is create an Outbound connector. This connector will be used by the mail flow rule that we'll set up in Step 2. In this connector, you'll select where messages it receives originate (such as a mailbox in your Microsoft 365 or Office 365 organization), the type of organization where the messages will be sent (such as your on-premises servers), the security that should be applied to the connection, and name or IP address of the target server. If you want to learn more about how to create connectors, check out Configure mail flow using connectors.

  1. In the EAC, go to Mail flow > Connectors. click New Add Icon to create a new connector.

  2. In the From: drop-down box, choose Office 365.

  3. In the To: drop-down box, choose either Your organization's email server or Partner organization if you want to connect to a server other than your organizations.

    route to and from options

  4. Name the connector and add a description. If you want to turn the connector on immediately, check Turn it on. Click Next.

    name connector

  5. Choose Only when I have a transport rule... and click Next.

    transport rule option

  6. Specify one or more smart hosts to which Microsoft 365 or Office 365 will deliver email messages.

    add host

  7. Define your Transport Layer Security (TLS) settings depending on your security needs.

    define TLS settings

  8. Review your new connector configurations and click Next to validate the connector.

Step 2: Use the EAC to create a mail flow rule

Now that we've created a connector, we need to create a mail flow rule that'll send mail to it based on the criteria you define. There are many conditions you can select from to control when messages should be sent to the connector.

  1. In the EAC, navigate to Mail flow > Rules. Click New Add Icon and choose Create a new rule....

  2. In the New rule window, name the rule. To see all the options available for the rule, click More options... at the bottom of the page.

    click more options

  3. For *Apply this rule if..., select The recipient... and has specific properties including any of these words. The select user properties box appears. Click Add Icon, and under User properties:, choose City. City is an Active Directory attribute made available for use by the rule. Specify the name of the city, such as New Orleans. Click OK, and then click OK again to close the select user properties box.

    apply rule if


    Check the accuracy of user attributes in Active Directory to ensure that the mail flow rule works as intended. > Note that outbound connector changes may take time to replicate.

  4. For *Do the following..., choose Redirect the message to... and then specify the following connector. The select connector box appears. Choose the Outbound connector you created previously.

    You can choose additional properties for the rule, such as the test mode and when to activate the rule.

  5. To save the connector, click Save.