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Copy file name to clipboardExpand all lines: defender-office-365/tenant-allow-block-list-teams-domains-configure.md
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- tier1
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description: Admins can learn how to block domains in Microsoft Teams using the Tenant Allow/Block List.
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ms.service: defender-office-365
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ms.date: 10/06/2025
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ms.date: 10/15/2025
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appliesto:
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- ✅ <a href="https://learn.microsoft.com/defender-office-365/eop-about" target="_blank">Default email protections for cloud mailboxes</a>
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- ✅ <a href="https://learn.microsoft.com/defender-office-365/mdo-about#defender-for-office-365-plan-1-vs-plan-2-cheat-sheet" target="_blank">Microsoft Defender for Office 365 Plan 1 and Plan 2</a>
> The feature described in this article is currently in Preview, isn't available in all organizations, and is subject to change.
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In all organizations with Microsoft Teams and cloud mailboxes, admins can create and manage block entries for domains in Microsoft Teams using the Tenant Allow/Block List. These blocked domain entries also appear on the **Organization settings** tab of the **External access** page in the Microsoft Teams admin center at <https://admin.teams.microsoft.com/company-wide-settings/external-communications> in the **Teams and Skype for Business users in external organizations** section:
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:::image type="content" source="media/tenant-allow-block-list-teams-domains.png" alt-text="Screenshot of the External access page in the Microsoft Teams admin center showing blocked domains." lightbox="media/tenant-allow-block-list-teams-domains.png":::
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- After you add the block entry for the domain in Teams, all new Teams communication from that organization is blocked. Block communication includes new Teams meetings, chats, channels, and calls. Existing Teams meetings, chats, channels, and calls are deleted.
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- On the **Organization settings** tab of the **External access** page in the Microsoft Teams admin center at <https://admin.teams.microsoft.com/company-wide-settings/external-communications>, the following settings are required to create and manage block entries for domains in Teams using the Tenant Allow/Block List:
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-**Teams and Skype for Business users in external organizations** must be one of the following values:
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-**Allow all external domains**
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-**Block only specific external domains**
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-**Allow my security team to manage blocked domains** must be :::image type="icon" source="media/scc-toggle-on.png" border="false"::: **On**.
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-**Teams and Skype for Business users in external organizations** must be **Allow all external domains** or **Block only specific external domains**.
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-**Allow my security team to manage blocked domains** must be :::image type="icon" source="media/scc-toggle-on.png" border="false"::: **On**.
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- The maximum number of domain block entries for Microsoft Teams is 4,000.
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