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Uploaded files never reach your agent in Microsoft 365 Copilot Chat

Mitigatedsince 8 July 2026

Last verified

Details & related

Assessment

Confidence
CorroboratedMultiple independent sources describe the same behaviour.
Severity
Blocking
Typical time lost
Hours

Identification

Publish & channelsM365 Copilot Chat

Verification & changes

  1. Verified

    Doc check by human: GitHub issue #15325 and dossier section B4 re-read during seed migration; Microsoft confirmation as a platform shortage stands, no published ETA.

  2. Change

    Provisionally approved by the Product Owner; external LLM quality review pending.

  3. Change

    Initial record created from the seed dossier (migration wave 1).

Related

Are you in the right place?

  • Users open your agent in Microsoft 365 Copilot Chat and attach a file.
  • The upload buttons work, and the file shows as attached.
  • The agent answers as if no file was ever sent.
  • No error or warning appears anywhere — for the user or for you.
  • The same agent handles image uploads in the Teams channel.

If instead the agent ignores images and files in every channel → see the file-processing toggle record (record planned). If files won't pass into a flow → see Files won't pass from the agent into a flow.

What's happening

The Microsoft 365 Copilot Chat channel strips file attachments before they reach your agent. The agent receives the message text with an empty attachment — logged as attachments=None in the GitHub issue. The user sees a successful upload, the agent sees nothing, and nobody gets a warning. It's like a mail room that removes every parcel and delivers only the envelope, telling no one. A Microsoft team member confirmed the behavior as a platform shortage, without a fix date (documented as of 2026-07-08). Teams supports image uploads; Microsoft 365 Copilot Chat does not — a parity gap between channels.

For technicians

GitHub issue #15325 (microsoft-365-agents-toolkit) traces the payload: the client renders the attachment, the agent receives attachments=None. The attachment data is stripped platform-side before delivery. No agent-side code, setting, or toggle can recover it. Microsoft classified this as a "Copilot platform shortage", not an Agents Toolkit bug. Because no error event is raised, telemetry stays empty as well.

How to fix it

Solution 1

Community workaround

Share a OneDrive or SharePoint link instead of uploading

  1. Upload the file to OneDrive or SharePoint.
  2. Select "Share" on the file.
  3. Select "Copy link".
  4. Confirm that the people using the agent can open that link.
  5. Paste the link into the chat message instead of attaching the file.

✅ You should now see: the agent's answer referring to the linked file — the content now reaches it.

Solution 2

Community workaround

Tell users up front not to upload

  1. In Copilot Studio, open "Topics".
  2. Open the "Conversation Start" system topic.
  3. Add one line to the greeting message.
  4. Use wording like:
Share files as OneDrive or SharePoint links — direct uploads do not reach me in this chat.
  1. Publish the change.

✅ You should now see: the greeting warning users before they attach anything.

Check that it worked

Open your agent in Microsoft 365 Copilot Chat as a normal user. Paste a link to a test document and ask a question about its content. Expected: the answer uses the document. A direct upload of the same file still fails silently — that part is Microsoft's to fix.

If it didn't work

  • Your greeting change has not propagated yet. Publishing reaches channels asynchronously — suspect number one. See Teams answers with an old version of your agent.
  • The agent cannot open the link. Check the sharing settings on the file. The people and connections behind the agent need access too.
  • Users keep attaching files anyway. The upload buttons stay visible; the platform does not hide them. Repeat the guidance wherever users start the chat.
  • You expected a setting to deliver the file. There is none. Microsoft confirmed the gap without a fix date (documented as of 2026-07-08).

Prevent it next time

  • Never design a workflow around direct file uploads in the Microsoft 365 Copilot Chat channel.
  • Put the link-instead-of-upload instruction into the greeting topic before rollout.
  • Retest upload behavior after platform updates — Microsoft may close the gap without an announcement.

Evidence

  • Community threadgithub.com

    The issue shows the agent receiving attachments=None because the platform strips attachment data before delivery, and a Microsoft team member confirms it as a Copilot platform shortage with no ETA.

  • MVP blogteam400.ai

    An independent 2026 limitations review documents that Copilot Studio agent capabilities differ by channel.