MC1133508 – (Updated) Microsoft Teams Integration with Microsoft Defender for Office Tenant Allow/Block List for blocking domains

Product:

Defender, Defender for Office 365, Defender XDR, Entra, Microsoft 365 admin center, Purview, Purview Communication Compliance, Teams

Platform:

Online, Web, World tenant

Status:

Launched

Change type:

Admin impact, New feature, Updated message, User impact

Links:

492985

Details:

Summary:
Microsoft Teams now integrates with Microsoft Defender for Office 365 Tenant Allow/Block List, enabling security admins to centrally manage blocked external domains in Teams. This feature, available with Defender Plan 1 or 2, blocks communications from specified domains, supports audit logging, and requires Teams admin enabling.

Details:
Updated December 16, 2025: We have updated the timeline. Thank you for your patience.
Introduction
We're introducing a new integration between Microsoft Teams and Microsoft Defender for Office 365 that enables security admins to manage blocked external domains in Teams using the Tenant Allow/Block List (TABL) in the Microsoft Defender portal. This feature enhances security by allowing organizations to centrally manage domain blocks across Microsoft 365 services.
This capability is available to customers with Microsoft Defender for Office 365 Plan 1 or Plan 2 and Microsoft Teams.
This message is associated with Microsoft 365 Roadmap ID 492985.
When this will happen

Targeted Release: We will begin rolling out late August 2025 and expect to complete by early September 2025.
General Availability (Worldwide): This is now generally available.

Change Category:
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Scope:
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Release Phase:
General Availability, Targeted Release

Created:
2025-08-12

updated:
2025-12-18

Task Type

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Docu to Check

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MS How does it affect me

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MS Preperations

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MS Urgency

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summary for non-techies**

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Direct effects for Operations**

Blocked Communications
If the change is implemented without preparation, users may experience unexpected blocks on communications from external domains, leading to disruptions in collaboration and communication.
   - roles: Security Admin, Teams Admin
   - references: https://learn.microsoft.com/defender-office-365/tenant-allow-block-list-teams-domains-configure, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=492985

User Experience Degradation
Users may face confusion and frustration due to sudden inability to communicate with external partners or clients, impacting productivity and user satisfaction.
   - roles: End User, Teams Admin
   - references: https://learn.microsoft.com/defender-office-365/tenant-allow-block-list-teams-domains-configure, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=492985

Compliance Monitoring Issues
Without proper preparation, the audit logs may not be correctly configured, leading to potential compliance issues and difficulties in tracking domain block actions.
   - roles: Compliance Officer, Security Admin
   - references: https://learn.microsoft.com/defender-office-365/tenant-allow-block-list-teams-domains-configure, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=492985

Configutation Options**

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Opportunities**

Enhanced Security Management
The integration allows security admins to centrally manage blocked domains, enhancing overall security posture. This means less risk of phishing and other malicious activities from external domains, improving user trust and safety in communications.
   - next-steps: Conduct a training session for security admins on how to effectively use the Tenant Allow/Block List feature. Set up a review process for blocked domains to ensure it aligns with organizational security policies.
   - roles: Security Admins, IT Admins, Compliance Officers
   - references: https://learn.microsoft.com/defender-office-365/tenant-allow-block-list-teams-domains-configure, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=492985

Audit and Compliance Improvements
With audit logging capabilities for actions taken on blocked domains, organizations can enhance compliance monitoring and reporting, ensuring that all actions are documented and traceable.
   - next-steps: Integrate audit logs with existing compliance tools and processes. Review compliance reporting procedures to incorporate data from the new logging features.
   - roles: Compliance Officers, IT Admins, Security Admins
   - references: https://learn.microsoft.com/defender-office-365/tenant-allow-block-list-teams-domains-configure, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=492985

Streamlined Communication Control
By allowing security teams to manage domain blocks directly through the Defender portal, the organization can reduce the administrative burden on Teams admins, leading to faster response times to security threats.
   - next-steps: Update administrative workflows to delegate domain management responsibilities to security teams. Establish clear communication channels between security and Teams admins for effective domain management.
   - roles: Security Admins, Teams Admins, IT Managers
   - references: https://learn.microsoft.com/defender-office-365/tenant-allow-block-list-teams-domains-configure, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=492985

Potentional Risks**

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Data Protection**

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IT Security**

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Hypothetical Work Council Statement**

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explanation for non-techies**

Imagine you're managing a guest list for a big event. You have a master list of people who are allowed to attend and a list of those who are not. Now, think of Microsoft Teams as your event, and the new integration with Microsoft Defender for Office 365 as your guest list manager. This integration allows security administrators to manage which external domains (like companies or organizations) can communicate with your team, much like deciding who can enter your event.

Previously, managing who could interact with your team was a bit scattered, like having multiple people with different lists for the same event. With this new feature, you can now centrally manage this list through the Microsoft Defender portal, making it easier to keep track of who’s allowed and who’s not. This is especially useful for security reasons, as it helps prevent unwanted or potentially harmful communications from unknown or suspicious domains.

For those with Microsoft Defender for Office 365 Plan 1 or 2, this integration is available and works across all Microsoft 365 services. It allows security admins to block or allow specific domains, much like a bouncer at your event checking names against the list. If a domain is blocked, any communication attempts from that domain are automatically stopped, ensuring that only trusted parties can interact with your team.

This feature also supports audit logging, which is like having a record of everyone who tried to get into your event, whether they were allowed in or not. This is useful for compliance and reporting, ensuring that your organization can demonstrate it is following security protocols.

To use this feature, Teams administrators need to enable a setting that allows the security team to manage these blocked domains. Think of it as giving the bouncer the authority to update the guest list as needed. This setting is off by default, so it needs to be turned on to start using the feature.

In summary, this integration simplifies the process of managing external communications in Microsoft Teams, providing a centralized, secure way to control who can interact with your organization, much like efficiently managing an event guest list.