Microsoft Defender for Office 365 provides robust email security by filtering out spam, phishing attempts, and malicious content. However, sometimes legitimate emails from trusted domains get flagged as spam. To ensure critical emails are not mistakenly blocked, you can whitelist a domain by modifying your Inbound Spam Policy in Microsoft Defender.
What is Domain Whitelisting in Microsoft Defender?
Whitelisting a domain means allowing emails from a specific domain to bypass spam filters, ensuring they are delivered directly to recipients' inboxes. This is useful when:
✅ Emails from trusted partners,
vendors, or clients are incorrectly marked as spam.
✅ Important notifications from
business-critical services are not reaching users.
✅ Internal company emails are getting filtered by Defender’s security policies.
By modifying your Inbound Spam Policy, you can prevent unnecessary email disruptions.
How to Whitelist a Domain in Microsoft Defender for Office
365
Step 1: Access Microsoft Defender Security Center
- Sign in to Microsoft Defender Security Center.
- In the left-hand menu, click on Email & Collaboration → Policies & Rules → Threat policies.
- Under Policies, select Anti-spam policies.
Step 2: Modify the Inbound Spam Policy
- Under the Anti-spam policies section, click Inbound policy (Default).
- Select Edit policy to modify the settings.
Step 3: Add a Trusted Domain to the Allow List
- Scroll down to the Allow & Block Lists section.
- Click on Edit allowed and blocked senders and domains.
- Under Allowed domains, click Add a domain.
- Enter the domain name (e.g., example.com).
Click Save to apply the changes.
💡 Tip: If you need to whitelist multiple domains, you can add each one separately.
Step 4: Adjust Spam Filtering Settings (Optional)
- To further refine your spam filter settings:
- In the Inbound Spam Policy, navigate to Advanced Spam Filtering (ASF) settings.
- Adjust the Bulk email threshold and Phishing thresholds based on your organization’s requirements.
- Click Save to update the settings.
Step 5: Validate and Test the Whitelisted Domain
- Send a test email from the whitelisted domain to ensure it reaches the inbox.
- Check the Microsoft Defender Email Trace Report to confirm successful email delivery:
- Go to Microsoft 365 Security & Compliance Center → Reports → Message Trace.
- Enter the sender’s domain and check the email status.
Best Practices for Whitelisting Domains in Microsoft
Defender
✔ Whitelist only trusted domains
to prevent potential security risks.
✔ Regularly review and update
the allow list to keep it up to date.
✔ Use Transport Rules (Exchange
Admin Center) if you need more granular control over email filtering.
✔ Monitor email logs to detect any unusual activity from whitelisted domains.
Whitelisting a domain in Microsoft Defender for Office 365
ensures that important emails are not mistakenly blocked or marked as spam. By
modifying your Inbound Spam Policy, you can maintain a secure yet efficient
email environment for your organization.
💡 How do I remove a domain from the whitelist?
Go to Microsoft Defender → Anti-spam policies → Edit Allow
List → Remove the domain and save changes.
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