Microsoft Teams: File attachment control now enabled by default in external 1:1 and group chats [MC1181772]

Message ID: MC1181772

[Introduction]

We’re improving external collaboration in Microsoft Teams by enabling file attachments and Loop sharing in 1:1, group and meeting chats with external users. This update improves the collaboration experience for Files and Loop and add a new control for IT admins. Specifically, Files and Loop components will be shared automatically with external participants in the chat and won’t require any action by the sender by default. Additionally, Entra B2B Guests in your organization will be able to attach and share files from their home tenant’s OneDrive or SharePoint. 

This change applies to Teams for Windows desktop, Mac desktop, and web and is associated with Roadmap ID 492625.

Screenshot 1: Files are automatically provisioned.

Screenshot 2: Files shared have an external label and always open on Web.

[When this will happen:]

• Targeted Release: Rollout begins late October 2025; expected to complete by mid-November 2025
• General Availability (Worldwide): Rollout begins mid-January 2026

[How this affects your organization:]

Who is affected:

All Microsoft Teams users in your organization who participate in 1:1, group, or meeting chats with external users, including guest and Teams for Free users.

What will happen:

With this update:

• Unless the user chooses to share File and Loop by pasting links, external users in chat will be automatically provisioned to allow frictionless collaboration.
• You can disable automatic provisioning and have the user change permissions manually by using policy controls.
• If disabled, users will have to manually provision the file to users in the chat.
• Guest users will be able to upload files from their home tenant’s OneDrive and SharePoint.
• Files shared by external users will continue to display an External tag for clarity.
• Loop components will now be rendered inside external chats in Teams.
• Recipients will access File and Loop components as B2B guests within the resource tenant. If they are not already added as guests, they will need to give consent and might need to complete MFA, depending on your company’s B2B policy, before viewing the chat content.

What you can do to prepare:

• No action is required to enable the feature—it will be automatically available as the rollout progresses.
• To disable the automatic provisioning behavior for files and loops set the AutoShareFilesInExternalChats attribute of TeamsMessagingPolicy to Disabled. Learn more: Set-CsTeamsMessagingPolicy documentation.
• To provide seamless Loop access experience for external users, we recommend turning on Entra B2B Guest Access. Refer to: Microsoft Entra B2B integration for SharePoint & OneDrive – SharePoint in Microsoft 365 | Microsoft Learn.
• For configuration guidance, refer to: Set-CsTeamsFilesPolicy documentation (documentation will be updated before rollout).

Compliance considerations

Compliance Area	Impact
New communication method between tenants	Enables file sharing in external chats, expanding cross-tenant collaboration
Admin control available	Admins can disable the feature via PowerShell
Can be controlled through Entra ID group membership	Policy can be scoped using Entra ID groups
Data processing changes	Files shared in external chats are tagged and stored per existing Teams file sharing protocols

Source: Microsoft

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