542189 – Microsoft Defender for Office 365: Admins can block external users in Microsoft Teams from Defender Portal

Product:

Defender, Defender for Office 365, Teams

Platform:

Web, World tenant

Status:

Rolling out

Change type:

Links:

MC1200058

Details:

Security admins with Defender for Office 365 Plan 1 and above can block external users from sending messages, calls, meetings invitation over Microsoft Teams via the Tenant Allow Block List in Microsoft Defender portal

Change Category:
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Scope:
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Release Phase:
General Availability

Created:
2025-12-18

updated:
2026-01-07

Docu to Check

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MS workload name

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summary for non-techies**

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Direct effects for Operations**

Please, look at the most relevant linked item for details

explanation for non-techies**

Microsoft has introduced a new feature for security administrators using Microsoft Defender for Office 365 Plan 1 and above. This feature allows admins to block external users from sending messages, making calls, or sending meeting invitations over Microsoft Teams. This can be done through the Tenant Allow Block List in the Microsoft Defender portal.

Think of this feature like a bouncer at a club. Just as a bouncer controls who can enter the club, this feature allows admins to control who can communicate with their organization via Microsoft Teams. If an external user is not on the approved list, they won't be able to send messages or invitations, much like how a bouncer would prevent someone not on the guest list from entering the club.

This change is designed to enhance security by giving organizations more control over their communications. It helps prevent unwanted or potentially harmful interactions from external sources, ensuring that only trusted contacts can reach out to team members. This is particularly useful for organizations that need to maintain strict communication policies and want to protect their internal communications from external threats.