Security Policy Errors

How to Manage Outbound Email Quarantine in Microsoft 365

WPS Editor Oct 7, 2026 869 views

Question details

The user needs to manage or temporarily disable outbound email quarantine in Microsoft 365 because outgoing organizational emails are being unexpectedly blocked.

How to Manage Outbound Email Quarantine in Microsoft 365

Product: Microsoft 365
Device & OS: not provided
Scenario: Managing outbound spam filter policies to ensure legitimate outgoing organizational emails are successfully delivered.
Observed behavior: Messages sent from the organization's domain are being quarantined and not released, requiring an adjustment to outbound filtering settings.

Before you start

Before modifying outbound filtering policies, ensure that your domain and user accounts have not been compromised by unauthorized senders. Temporarily disabling outbound protection without investigating the root cause can expose your organization to severe security risks and potential domain blacklisting.

Solution 1Recommended

Review and Adjust the Outbound Spam Filter Policy

Use the Microsoft Defender portal to review outbound spam policies, investigate quarantined messages, and release false positives safely.

Disabling outbound filtering permanently is highly risky. Instead, administrators should investigate why the emails are being flagged, release legitimate emails manually, and carefully adjust the default outbound policy.

Access Microsoft Defender

Navigate to Anti-spam policies

Go to 'Policies & Rules' in the left-hand navigation menu, select 'Threat policies', and then click on 'Anti-spam'.

Modify the outbound policy

Locate and click on the 'Anti-spam outbound policy (Default)' or your organization's custom outbound policy to review its configuration and sending limits.

Release legitimate messages

Investigate currently quarantined messages in the portal. Manually release legitimate emails and report them as false positives to train the filter and improve future accuracy.

Review and Adjust the Outbound Spam Filter Policy

Security Warning: Avoid permanently disabling outbound filtering. If you must turn it off for troubleshooting, use a temporary, controlled policy change only after fully understanding the security impact.

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Frequently Asked Questions

Why are my outbound emails being quarantined in Microsoft 365?

Microsoft 365 automatically quarantines outbound emails if they trigger anti-spam policies. This usually happens due to a high volume of bulk emails being sent, suspicious content within the emails, or a potentially compromised account sending unauthorized spam.

Can I permanently disable outbound email filtering in Microsoft Defender?

While technically possible through policy modifications, permanently disabling outbound filtering is strongly discouraged. Doing so creates a severe security risk and increases the likelihood of your domain being blacklisted by external email providers.

How do I release an email that was mistakenly quarantined?

As an administrator, navigate to the Microsoft Defender portal, select the Quarantine page under 'Review', select the mistakenly blocked messages, and click 'Release'. You should also choose to report them as false positives to prevent future occurrences.

How can I tell if an email account has been compromised and restricted?

Check the 'Restricted entities' page in the Microsoft Defender portal under the 'Review' section. If a user exceeds outbound sending limits or exhibits highly unusual sending patterns, Microsoft 365 will automatically restrict the account from sending messages and list them there.

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