Security Policy Errors

Why Blocked Senders Still Appear in Microsoft 365 Quarantine

Emma Brown Sep 28, 2026 870 views

Question details

Users want to know why emails from blocked addresses or domains are still routed to the Microsoft 365 quarantine instead of being completely rejected by the server.

Why Blocked Senders Still Appear in Microsoft 365 Quarantine

Product: Microsoft 365
Device & OS: not provided
Scenario: A user has blocked specific email senders or domains to prevent spam, but notices these blocked messages continue to accumulate in the daily quarantine list.
Observed behavior: Blocking an address successfully prevents the email from reaching the inbox, but the message is still accepted by the server and placed into quarantine instead of being bounced or rejected outright.

Before you start

Verify that you have administrative access to the Microsoft 365 Defender portal, as changing organization-wide quarantine and rejection behaviors requires appropriate admin roles.

Solution 1Recommended

Modify Anti-Spam Policies in Microsoft 365 Defender

Configure your organization's anti-spam policies to change how Microsoft 365 handles blocked senders, allowing you to reject messages rather than quarantining them.

By default, the personal blocked-sender list only prevents emails from reaching the inbox. To stop messages from reaching the quarantine, an administrator must update the tenant's threat policies or create mail flow rules to reject the emails at the server level.

Access Microsoft 365 Defender

Log in to the Microsoft 365 Defender portal using your administrator credentials and navigate to 'Email & collaboration' in the left menu.

Navigate to Threat Policies

Go to 'Policies & rules', then select 'Threat policies', and click on 'Anti-spam' under the Policies section.

Edit the Anti-Spam Inbound Policy

Select the 'Anti-spam inbound policy (Default)' or your custom policy, scroll to the 'Actions' section, and click 'Edit actions'. Change the action for spam or high-confidence spam to 'Reject message' instead of 'Quarantine message'.

Modify Anti-Spam Policies in Microsoft 365 Defender

Admin Privileges Required: You must be a Global Administrator or Security Administrator in your Microsoft 365 tenant to access and modify these anti-spam policies.

Solution 2

Configure Exchange Mail Flow Rules to Drop Messages

Create a specific transport rule in the Exchange Admin Center to silently drop or bounce emails from specific persistent spam domains before they hit the quarantine.

Solution 3

Update Personal Junk Email Options in Outlook

Ensure your local Outlook client is properly configured to filter junk email and report persistent spam to Microsoft.

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Frequently Asked Questions

Why does the blocked sender list not stop emails from going to quarantine?

The personal blocked sender list is designed exclusively to prevent unwanted emails from reaching your primary inbox. It does not dictate server-level rejection, meaning the Microsoft 365 server still receives the email and routes it to quarantine according to your organization's overarching security policies.

Can I permanently reject emails instead of quarantining them?

Yes, but this requires an IT administrator. A Microsoft 365 admin can modify the organization's Anti-spam inbound policies in the Defender portal to 'Reject message' instead of 'Quarantine message', or they can create Exchange mail flow rules to silently drop emails from specific domains.

How do I review the emails currently in my Microsoft 365 quarantine?

You can access your personal quarantined messages by logging into the Microsoft 365 Defender portal at security.microsoft.com. Navigate to 'Email & collaboration', select 'Review', and click on 'Quarantine' to view, release, or delete trapped messages.

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