Security Policy Errors

How to Fix a Website Blocked as Malicious by Microsoft Defender

Rana Garcia Sep 30, 2026 870 views

Question details

A website is incorrectly flagged as malicious by Microsoft Defender, causing related emails to be sent to the Junk folder with a questionable-domain warning.

How to Fix a Website Blocked as Malicious by Microsoft Defender

Product: Microsoft Defender for Office 365
Device & OS: not provided
Scenario: A site owner discovers their website domain is being blocked or flagged in emails sent to Office 365 users.
Observed behavior: Emails containing the website's domain are automatically routed to the Junk folder, and Microsoft Defender displays a warning that the domain is questionable or malicious.

Before you start

Before submitting a review request, ensure your website is thoroughly scanned for malware and that your email authentication protocols (SPF, DKIM, and DMARC) are correctly configured.

Solution 1Recommended

Submit a False Positive Review to Microsoft SmartScreen

Use the Microsoft Defender SmartScreen feedback system to request a re-evaluation of your blocked website.

Microsoft Defender SmartScreen can block websites that are reported as malicious or contain phishing indicators. If this is a false positive, submitting the site for an official review is the primary way to remove the block.

Access the SmartScreen Feedback Portal

Navigate to the Microsoft Defender SmartScreen feedback portal in your web browser.

Enter Your Website Details

Enter the URL of your blocked website and select the option indicating that you are the site owner.

Provide a Justification

Provide a detailed explanation stating that you believe the classification is a false positive and outline the security checks you have performed.

Submit for Investigation

Submit the form and wait for Microsoft's security team to investigate and remove the malicious flag.

Submit a False Positive Review to Microsoft SmartScreen

Review Time: Microsoft's investigation process may take a few days. Ensure your DNS and email authentication settings remain flawless during this period.

Solution 2

Audit Website Security and Email Authentication

Proactively secure your domain to prevent automated security systems from flagging it as a threat.

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Frequently Asked Questions

Why did Microsoft Defender suddenly flag my website as malicious?

Microsoft Defender relies on automated scanning and user reports. Sudden flagging can occur due to missing email authentication (SPF/DKIM), hosting on a shared server with malicious sites, or undetected malware on your site.

How long does it take for Microsoft to remove the malicious domain warning?

After submitting a false positive report through the SmartScreen feedback process, it typically takes 24 to 72 hours for Microsoft to review and lift the restriction if the site is clean.

Can incorrect DNS settings cause emails to go to the Junk folder?

Yes. If your domain lacks proper SPF, DKIM, or DMARC records, Microsoft Defender for Office 365 cannot verify the sender's identity, often resulting in emails being marked as junk or phishing attempts.

How can I check if my website has been blacklisted by other services?

You can use free online domain reputation tools and blacklist checkers (such as MXToolBox or Google Safe Browsing) to see if your website domain appears on any other security blocklists.

Microsoft Office Security Issues