How to Configure Office 365 to Scan Only Selected Domains Outbound

Use the steps in this article if you have multiple domains within your Office 365 tenant and you want to scan only certain domains outbound.

Step 1. Create the Connector

1. Log in to the Office 365 admin center, and go to Admin centers > Exchange.
2. In the left pane, click mail flow, and click connectors.
3. Click the + symbol and use the wizard to create a new connector.
4. From the From  drop-down menu, select Office 365, and from the To drop-down menu, select Partner organization.
5. Enter a Name and (optional) Description to identify the connector:
   
6. Click Next. Select Only when I have a transport rule set up that redirects messages to this connector:
   
7. Click Next. Select Route email through these smart host, and click on your outbound hostname:
   
8. Click Next. Use the default setting, Always use Transport Layer Security (TLS) to secure the connection (recommended) > Issues by Trusted certificate authority (CA):
   
9. Click Next. In the confirmation page, verify your settings and click Next. Office 365 runs a test to verify your settings:
   
10. When the verification page displays, enter a test email address, and click Validate. Once the verification is complete, your mail flow settings are added.

Step 2. Create Transport Rule

1. Log in to the Office 365 admin center, and go to Admin centers > Exchange.
2. In the left pane, click  mail flow, and click  rules.
3. Click the + symbol, and click Create new rule.
4. In the new rule page, enter a Name to represent the rule.
5. Click more options towards the bottom of the page.
6. From the Apply this rule drop-down menu, select The sender is located > is external/internal > Inside the organization.
7. From the Do the following drop-down menu, select Redirect the message to…  > the following connector, and select the connector you defined in Step 1. Create the Connector.
8. Click Add Exception.
9. From the drop-down menu, select The Recipient is located > is external/internal > Inside the organization.
10. Click Add Exception.

11. From the drop-down menu, select The sender address matches > address matches any of these text patterns, and enter the domain(s) you want to exclude from outbound scanning.

    You must use regular expressions when entering the domain. For example, if you want to exclude the domain mycompany.com, you would type: '@mycompany\.com$'

    Contact Barracuda Networks Support if you need assistance.

12. Choose Enforce as the mode, and select Stop processing more rules:
     
13. Click Save.