Microsoft Teams – Drag and Drop File Sharing Fails in External Chats

Ahmed 0 Reputation points
2026-08-21T06:57:33.2766667+00:00

Dear Microsoft Support,

We are experiencing an issue with file sharing in Microsoft Teams external (federated) chats.

File sharing with external users is enabled and works correctly when using the Attach File button. However, when users drag and drop a file or image directly into the external chat, Teams displays the following error:

“External sharing is not allowed.”

We tested multiple methods with the following results:

  • Attach File – Teams Windows/Desktop: Works
  • Attach File – Teams Web: Works
  • File sharing – Teams iOS: Works
  • Copy/paste screenshot into external chat: Works
  • Drag & drop JPG: Fails
  • Drag & drop PDF: Fails
  • Drag & drop TXT: Fails
  • Drag & drop in Teams Desktop: Fails
  • Drag & drop in Teams Web: Fails

We have verified the Teams Files Policy:

Get-CsTeamsFilesPolicy -Identity Global | Format-List *

Identity                            : Global
NativeFileEntryPoints               : Enabled
SPChannelFilesTab                   : Enabled
DefaultFileUploadAppId              :
FileSharingInChatswithExternalUsers : Enabled

We have also verified the Teams Messaging Policy:

Get-CsTeamsMessagingPolicy -Identity Global |
Select-Object Identity,AutoShareFilesInExternalChats

Identity AutoShareFilesInExternalChats
-------- -----------------------------
Global   Enabled

Additionally:

  • SharePoint external sharing is allowed.
  • OneDrive external sharing is allowed.
  • No third-party file upload application is configured (DefaultFileUploadAppId is blank).
  • The issue occurs in both the Teams Desktop application and Teams Web.
  • Normal file attachment to the same external chats works successfully.

According to Microsoft documentation, when external chat file sharing is enabled, users should be able to share files by both uploading a file and dragging and dropping a file into the message box.

Could you please investigate whether there is a backend/service-side issue or additional tenant-level configuration affecting drag-and-drop file sharing in external chats?

Please let us know if you require any additional logs, tenant information, diagnostic data, or reproduction details.

Microsoft Teams | Microsoft Teams for business | Chats | Share photos, files, and video

1 answer

Sort by: Newest
Most helpful Newest Oldest
  1. Ana Le 2,345 Reputation points Independent Advisor
    2026-08-21T07:24:14.1733333+00:00

    Hi @Ahmed,

    Thank you for providing the detailed testing results.

    Based on the information provided, your understanding aligns with the Microsoft documentation. When external chat file sharing is enabled, users are expected to be able to share files both by uploading a file and by dragging and dropping a file into the message compose area. Microsoft also identifies FileSharingInChatsWithExternalUsers as the required Teams Files policy setting for this capability.

    The key detail in your testing is that file sharing itself is already working. Files can be successfully shared using the Attach File button in the same federated conversations, which indicates that external file sharing is not being blocked entirely.

    Since:

    • Attach File works successfully
    • Drag-and-drop fails for multiple file types
    • The issue reproduces in both Teams Desktop and Teams Web
    • SharePoint and OneDrive external sharing are enabled

    the behavior appears to be isolated to the drag-and-drop upload workflow rather than the overall external file-sharing configuration.

    One remaining check would be to confirm the effective Teams policies applied to an affected user, since the PowerShell output provided shows the Global policy settings. Microsoft documents that a policy assigned directly to a user or through a group can take precedence over the Global policy.

    You can review the policy assignments for an affected user with:

    *Get-CsUserPolicyAssignment -Identity *****@domain.com

    If the affected user is receiving the expected Teams Files and Messaging policies, then based on the currently published documentation, I am not aware of a separate Teams policy that controls drag-and-drop uploads independently from standard file attachments in external chats.

    As this is a user-to-user community forum, I do not have access to tenant-level diagnostics, backend telemetry, or service-side configuration. Given the evidence provided, the next appropriate step would be open a Microsoft 365 support request so that Microsoft can review the service logs and determine whether this is a backend issue, product regression, or another tenant-specific condition.

    References:

    Was this answer helpful?

Your answer

Answers can be marked as 'Accepted' by the question author and 'Recommended' by moderators, which helps users know the answer solved the author's problem.