Security Policy Errors

Fix Microsoft Defender Flagging SendGrid Email Links as Malicious

Phi Hung Vo Sep 30, 2026 869 views

Question details

Users need a way to prevent Microsoft Defender from blocking their safe, opt-in SendGrid email links with a malicious website warning.

How to Fix Microsoft Defender Flagging SendGrid Links as Malicious

Product: Microsoft 365 / SendGrid
Device & OS: not provided
Scenario: Sending informational, opt-in emails via SendGrid to recipients who are using Microsoft 365.
Observed behavior: Microsoft Defender intercepts the HTTPS SendGrid tracking links and displays a malicious website warning to recipients, even though the links work safely outside the affected organization.

Before you start

Ensure you have administrator access to your Microsoft 365 Defender portal to submit false-positive reports, and access to your SendGrid account settings to review click-tracking configurations.

Solution 1Recommended

Submit a False-Positive Report to Microsoft Defender

Use this recommended approach to officially notify Microsoft that the SendGrid URLs are safe, prompting them to adjust their security filters.

Microsoft Defender uses automated systems to detect suspicious redirect chains often associated with phishing. By submitting a false-positive report, you request a manual review of your sending domain and tracking infrastructure.

Access the Microsoft 365 Admin Center

Log in to the Microsoft 365 admin center using your administrator credentials and navigate to the Security or Microsoft Defender portal.

Locate the Blocked URL Alert

Go to the 'Incidents & alerts' section, find the specific alert related to the blocked SendGrid URL, and select the flagged email or link.

Submit for Review

Choose the option to 'Submit to Microsoft for review' or 'Report as clean'. Provide necessary details confirming that the email is an opt-in informational message and that the redirect chain is expected.

Check SSL and Domain Configuration

While waiting for the review, verify that your SendGrid sender authentication (SPF, DKIM, DMARC) is correctly set up and that SSL for your custom tracking domain is properly configured.

Submit a False-Positive Report to Microsoft Defender

Review Processing Time: Microsoft typically processes false-positive submissions within 24 to 48 hours. You may need to coordinate with Microsoft Support if the issue persists.

Solution 2

Modify the URL Path Architecture

Use this workaround if Defender continues to block specific URLs despite false-positive submissions.

Solution 3

Disable Click Tracking in SendGrid

Use this quick fix if you urgently need emails to be delivered without warnings and do not require link engagement metrics.

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Frequently Asked Questions

Why is Microsoft Defender suddenly blocking my SendGrid links?

Microsoft Defender continuously updates its threat intelligence algorithms. It frequently flags third-party redirect trackers (like those used by SendGrid) as potentially malicious because attackers often use similar redirect techniques to hide phishing URLs. A recent policy update or a drop in your custom domain's reputation can trigger these blocks.

How long does a Microsoft Defender false-positive report take to process?

Once submitted through the Microsoft 365 admin center, false-positive reports are typically reviewed within 24 to 48 hours. However, complex cases involving third-party redirect chains may require further correspondence with Microsoft Support.

Is there a way to keep click tracking without getting flagged?

Yes. Setting up a Custom SSL configuration for your tracking links (using SendGrid's Custom Domain feature) and ensuring your sender authentication (SPF, DKIM, DMARC) is perfectly aligned can significantly improve your domain's reputation, reducing the likelihood of Microsoft Defender flagging your tracking links.

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