How to Allowlist a Domain in Microsoft 365

Allowlisting a domain in Microsoft 365 is a crucial process for businesses to ensure that emails from trusted sources are reliably delivered, without being marked as spam. This is especially important for maintaining communication integrity and security. In this guide, we’ll walk you through the process of allowlisting a domain in Microsoft 365 to ensure smooth email communication.

What is Domain Allowlisting?

Domain allowlisting, also known as domain whitelisting, is the practice of ensuring that emails from trusted domains bypass spam filters and other security checks within Microsoft 365. By allowlisting a domain, you ensure that legitimate emails from specific sources are always delivered to the recipients’ inboxes. This minimizes the risk of critical communications being incorrectly flagged as spam.

Steps to Allowlist a Domain in Microsoft 365

Follow these simple steps to allowlist a domain within your Microsoft 365 environment:

1. Access the Microsoft 365 Admin Center

Log into your Microsoft 365 Admin Center with your admin credentials. From the Microsoft 365 home page, navigate to the Admin app.

2. Navigate to the Exchange Admin Center

Once logged in, go to the Admin Centers section, then click on Exchange to access the Exchange Admin Center, where email-related settings are managed.

3. Go to Mail Flow Settings

In the Exchange Admin Center, click on Mail Flow in the left-hand menu. Then, under the Mail Flow section, click on Rules to manage transport rules for processing emails.

4. Create a New Transport Rule

Click on the + button to create a new transport rule. Give the rule a clear name, such as “Allowlist Domain: [Your Domain Name]”, so you can easily identify it later.

5. Define the Conditions

In the New Rule window, under the Apply this rule if… section, select The sender > domain is and then enter the domain you wish to allowlist. For example, to allowlist emails from example.com, input @example.com.

6. Set the Actions

Under Do the following…, choose Modify the message properties > Set the spam confidence level (SCL) and set it to Bypass spam filtering. This ensures that emails from the allowlisted domain will not be flagged as spam. You can also add other actions, like applying a message header to identify allowlisted emails.

7. Configure Exceptions (Optional)

If necessary, you can add exceptions to the rule to refine when it should apply. This is useful if you need to fine-tune which emails should be allowlisted under specific conditions.

8. Review and Save the Rule

Review the rule to ensure it matches your allowlisting needs. Once confirmed, click Save to activate the transport rule.

9. Verify and Monitor the Rule

After setting up the allowlist rule, it’s important to test its effectiveness. Send test emails from the allowlisted domain to check if they are delivered successfully and not marked as spam. Regularly monitor the Mail Flow Reports and Message Trace Logs in the Admin Center to verify that the rule is working as expected.

Best Practices for Domain Allowlisting

To maximize the effectiveness of domain allowlisting in Microsoft 365, consider the following best practices:

• Regularly Review the Allowlist: Continually update your allowlist to reflect new trusted domains or any changes in your organization’s needs.

• Educate Users: Encourage users to report suspicious emails, even from allowlisted domains. This helps maintain a high level of security.

• Integrate with Other Security Measures: Combine domain allowlisting with other Microsoft 365 security tools, such as Advanced Threat Protection (ATP), to enhance protection against evolving threats.

Additional Considerations

• Tenant Allowlist vs. Transport Rule: Microsoft 365 offers a tenant allowlist feature that allows administrators to specify entire domains or IP addresses as trusted. However, transport rules provide more detailed control and customization over allowlisting criteria.

• Third-Party Services: If your organization uses third-party email filtering services alongside Microsoft 365, ensure that the allowlist configurations are synchronized across all platforms to maintain consistency.

Conclusion

Allowlisting domains in Microsoft 365 is an essential step to ensure reliable and secure email communication for your organization. By following the steps outlined above, you can prevent legitimate emails from being mistakenly marked as spam. Regular monitoring and adjusting of allowlist configurations are key to adapting to changes in your organization’s needs and maintaining robust email security.