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How do I configure Microsoft 365 to route outbound mail through SecurityGateway?

Follow the steps below to configure Microsoft 365 (formerly Office 365) to route outbound mail through SecurityGateway.

  1. Log in to the Microsoft 365 admin center
  2. Click Admin/Exchange/Exchange Admin Center
  3. Select Mail Flow > Connectors
    • All currently existing connectors for your organization appear
  4. Click on the plus symbol (+) to add a new connector
  5. Under Select your mail flow scenario, select the following:
    • From: Microsoft 365
    • To: Partner organization
  6. Click Next
  7. Type a name and description for the new connector
  8. Check Turn it on and click Next
  9. Ensure Only when email messages are sent to these domains is checked, and then click the plus (+) icon
  10. In the add domain dialog box, type a single asterisk (*) to use as a wildcard, and then click OK
    • This forwards your outbound email to SecurityGateway.
  11. Select Route email through these smart hosts, and then click on the plus (+) icon
    • The add smart host dialog box appears
  12. Type the fully-qualified domain name (FQDN) of your SecurityGateway server. The FQDN is typically in the format hostname.domain.com.
  13. Click Save, and then click Next
  14. Choose if you want to have all emails use TLS when sending to SecurityGateway, and then click Next.
  15. To validate the connector, type a recipient email address on a domain outside of your organization.
  16. Once the connector is successfully validated, click Save.