check before: 2026-01-01
Product:
Defender, Defender for Office 365, Defender XDR, Microsoft 365 admin center, Teams
Platform:
Online, Web, World tenant
Status:
In development
Change type:
Admin impact, New feature, Updated message
Links:
Details:
Summary:
Starting mid-February 2026, admins can block external Microsoft Teams users via the Tenant Allow/Block List in the Microsoft Defender portal, controlling access and deleting existing communications. This applies to Teams and Defender XDR, with audit logging and limits of 4,000 domains and 200 emails blocked.
Details:
Updated January 23, 2026: We have updated the timeline. Thank you for your patience.
[Introduction]
We're introducing an integration between Microsoft Teams and Microsoft Defender for Office 365 that allows security admins to manage blocked external users in Teams through the Tenant Allow/Block List (TABL) in the Microsoft Defender portal. This centralized approach enhances security and compliance by enabling organizations to control external user access across Microsoft 365 services.
This message is associated with Roadmap ID 542189.
[When this will happen:]
General Availability (Worldwide): Rollout begins mid-February 2026 (previously early January) and is expected to complete by end of February 2026 (previously mid-January).
Change Category:
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Scope:
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Release Phase:
General Availability
Created:
2025-12-19
updated:
2026-01-24
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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summary for non-techies**
Starting in mid-February 2026, Microsoft Teams and Microsoft Defender for Office 365 will allow admins to block external users and domains from communicating with their organization, manage these lists through the Microsoft Defender portal, and maintain audit logs for security and compliance.
Direct effects for Operations**
Blocking External Users in Teams
If the change is implemented without proper preparation, users may experience disruptions in communication as incoming messages, calls, and meetings from blocked external users will be prevented, leading to potential confusion and frustration.
- roles: Security Admins, End Users
- references: https://learn.microsoft.com/microsoft-365/security/office-365-security/tenant-allow-block-list, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=542189
Deletion of Existing Communications
Existing communications from blocked users will be automatically deleted, which may result in loss of important information and context for ongoing projects or discussions, negatively impacting user experience.
- roles: End Users, Project Managers
- references: https://learn.microsoft.com/microsoft-365/security/office-365-security/tenant-allow-block-list, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=542189
Audit Logging and Compliance
Without preparation, the lack of awareness about audit logging may lead to compliance issues, as actions taken to block users will be tracked, but if users are not informed, they may inadvertently violate internal policies.
- roles: Security Admins, Compliance Officers
- references: https://learn.microsoft.com/microsoft-365/security/office-365-security/tenant-allow-block-list, https://www.microsoft.com/microsoft-365/roadmap?filters=&searchterms=542189
Configutation Options**
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Opportunities**
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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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DPIA Draft**
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explanation for non-techies**
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change history
| Date | Property | old | new |
| 2026-01-24 | MC MessageTagNames | New feature, Admin impact | Updated message, New feature, Admin impact |
| 2026-01-24 | MC Summary | Admins can now block external users in Microsoft Teams via the Tenant Allow/Block List in the Microsoft Defender portal, controlling access and communications. This feature, rolling out January 2026, supports up to 4,000 domains and 200 emails, with audit logging and no impact on existing Teams settings. | Starting mid-February 2026, admins can block external Microsoft Teams users via the Tenant Allow/Block List in the Microsoft Defender portal, controlling access and deleting existing communications. This applies to Teams and Defender XDR, with audit logging and limits of 4,000 domains and 200 emails blocked. |
| 2026-01-24 | MC Last Updated | 12/19/2025 08:08:18 | 2026-01-24T01:51:04Z |
| 2026-01-24 | MC Messages | [Introduction]
We're introducing an integration between Microsoft Teams and Microsoft Defender for Office 365 that allows security admins to manage blocked external users in Teams through the Tenant Allow/Block List (TABL) in the Microsoft Defender portal. This centralized approach enhances security and compliance by enabling organizations to control external user access across Microsoft 365 services. This message is associated with Roadmap ID 542189. [When this will happen:] General Availability (Worldwide): Rollout begins early January 2026 and is expected to complete by mid-January 2026. | Updated January 23, 2026: We have updated the timeline. Thank you for your patience.
[Introduction] We're introducing an integration between Microsoft Teams and Microsoft Defender for Office 365 that allows security admins to manage blocked external users in Teams through the Tenant Allow/Block List (TABL) in the Microsoft Defender portal. This centralized approach enhances security and compliance by enabling organizations to control external user access across Microsoft 365 services. This message is associated with Roadmap ID 542189. [When this will happen:] General Availability (Worldwide): Rollout begins mid-February 2026 (previously early January) and is expected to complete by end of February 2026 (previously mid-January). |
| 2026-01-24 | MC Title | Microsoft Defender for Office 365: Admins can block external users in Microsoft Teams from Defender Portal | (Updated) Microsoft Defender for Office 365: Admins can block external users in Microsoft Teams from Defender Portal |
| 2026-01-24 | MC End Time | 02/13/2026 09:00:00 | 2026-03-30T10:00:00Z |
Last updated 3 weeks ago ago
