Security Policy Errors

How to Fix Microsoft Quarantining Domain Emails as High-Confidence Phishing

Aamir Naveed Akram Oct 12, 2026 869 views

Question details

Transactional emails containing custom domain URLs are incorrectly classified and quarantined by Microsoft as high-confidence phishing.

How to Fix Microsoft Quarantining Domain Emails as High-Confidence Phishing

Product: Microsoft Defender / Exchange Online
Device & OS: not provided
Scenario: Sending outbound transactional emails containing links to customer projects.
Observed behavior: Emails are blocked or quarantined by Microsoft as high-confidence phishing whenever the sender domain or URL appears in the message body or signature, ignoring local allow lists.

Before you start

Verify that your domain's email authentication records (SPF, DKIM, and DMARC) are fully properly configured and propagating, as Microsoft requires these to be valid before reviewing blocklist removal requests.

Solution 1Recommended

Contact Microsoft Professional Support for Domain Reputation Investigation

This is the most effective solution for high-confidence phishing classifications, as it requires Microsoft to manually remove your domain from their internal backend blocklists.

Adding your domain to local Safe Links or tenant-level allow policies usually will not override a 'high-confidence phishing' classification. This flag is applied globally by Microsoft's backend algorithms.

You must escalate the issue directly to Microsoft Support to have the domain's reputation investigated and cleared from filtering lists.

Open the Microsoft 365 Admin Center

Create a New Support Request

Navigate to the Support section, click on 'Help & support', and describe that outbound emails are being blocked as high-confidence phishing.

Request Blocklist Removal

Explicitly ask the Microsoft Professional Direct Support team to investigate your domain and website reputation, and request the domain be removed from any internal Microsoft blocklists.

Monitor Email Deliverability

Once support confirms the removal, continue monitoring your outbound emails for 48 to 72 hours, as the false-positive classification can sometimes return and require a follow-up.

Contact Microsoft Professional Support for Domain Reputation Investigation

Persistence may be required: It can sometimes take multiple follow-ups over several weeks to get a domain permanently whitelisted by Microsoft.

Solution 2

Submit False-Positive Reports via Microsoft Defender Explorer

Reporting incorrectly classified emails helps train Microsoft's automated filtering algorithms, even though it may not provide an immediate fix.

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Frequently Asked Questions

Why is Microsoft suddenly classifying my domain as high-confidence phishing?

Microsoft's automated filters may flag your domain due to recent changes in email volume, newly registered domains, shared hosting IPs, or links pointing to sites with a poor reputation score. This can occur even if your SPF, DKIM, and DMARC records are configured perfectly.

Will adding my domain to Safe Links fix the high-confidence phishing issue?

Generally, no. Tenant-level policies like Safe Links or local Exchange mail flow rules are usually bypassed when Microsoft's backend algorithms flag an email as 'high-confidence phishing'. You must contact Microsoft Support directly to address the root cause on their internal blocklist.

How long does it take for Microsoft Support to remove my domain from their blocklist?

Resolution times vary widely. While some blocks are lifted within 48 to 72 hours after initial contact, others may require persistent follow-up tickets over several weeks or even months before the false-positive block is permanently removed.

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