Teams will turn on file sharing in external chats, even where admins had switched it off

Teams will turn on file sharing in external chats, even where admins had switched it off

25 September 2026 — Microsoft has told administrators that file sharing in external, or federated, Microsoft Teams chats will be switched on by default. The notice, Message Center post MC1479514, was published on 25 September 2026. External chats are the one-to-one, group and meeting chats with people in other organisations that use Teams.

Not yet independently verified. This rests on Microsoft’s own Message Center post, read through a public archive because the admin centre requires sign-in; the one other write-up found restates it. No independent report of it was found, so every date here comes from the vendor's own page and is only as reliable as that page. We will update this when it can be confirmed, and remove this note.

What changes, and when

• Rollout starts in late October 2026 and is expected to finish by late November 2026, across commercial tenants and the US government clouds.
• Users will be able to attach files directly in external chats. When a file is uploaded, Teams will automatically grant the chat's external participants permission to open it.
• Microsoft states that "this change applies even if your organization previously configured the setting as Disabled". Organisations that want it off must reapply the setting after the rollout.

That last point is what makes this more than a convenience feature. A tenant that deliberately blocked file sharing with outside parties will find it switched back on, without anyone in the organisation changing anything.

What still limits it

Microsoft says existing OneDrive and SharePoint sharing controls "continue to govern access", and advises reviewing SharePoint, OneDrive and Microsoft Entra external sharing settings. In practice, what an external person can open depends on those settings, so an organisation with tight SharePoint sharing is less exposed than one with loose defaults.

Who is affected

Every Microsoft 365 organisation that uses Teams federation, and especially those that switched external file sharing off for data-protection, confidentiality or regulatory reasons. Law firms, financial and healthcare organisations, and anyone with contractual limits on where client files may go should treat this as a change to their controls.

What to do

• Decide now whether file sharing in external chats should be allowed. If not, plan to reapply the block after the rollout reaches your tenant, not before, since Microsoft says a prior Disabled setting is overridden.
• Microsoft gives the command to turn it off as Set-CsTeamsFilesPolicy -Identity Global -FileSharingInChatsWithExternalUsers Disabled, and to check it with Get-CsTeamsFilesPolicy.
• If you want attachments but not automatic permissions, a separate setting, AutoShareFilesInExternalChats in the Teams messaging policy, can be disabled.
• Review SharePoint, OneDrive and Entra external sharing settings, which remain the real limit on access.
• If a managed provider runs your Microsoft 365 tenant, ask it to confirm the setting after late November, and add it to your regular configuration checks.

Sources

• Microsoft 365 Message Center MC1479514, File sharing enabled by default in external (federated) chats, via the public Message Center archive — 25 September 2026
• PUPUWEB: MC1479514 Microsoft Teams file sharing enabled by default in external (federated) chats — 26 September 2026
• Microsoft Learn: Share files and Loop in external chats (read 26 September 2026) — 26 September 2026