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As a guest I cannot attach files

In a foreign organization file uploads do not work for you. Guest permission limit that only the tenant admin of that org can loosen.

Last verified:

Affected systems

windows macos web ios android

Quick fixes

  • Send a OneDrive sharing link instead of attaching directly
  • Use channel files instead of 1:1 chat files (often allowed for guests)
  • Ask the guest tenant admin to enable external sharing

Why this happens

Microsoft restricts guests in foreign tenants by default. A typical default config:

  • Channel posts in a team: guests can write and upload files, because that lives in the team’s SharePoint library
  • 1:1 chats between guest and members: file upload often disabled because it would require the OneDrive of the guest or the member
  • Group chats with guests: similarly limited

As a guest you see an error on the attach button or no button at all.

Instead of attaching directly:

  1. Upload the file to your own OneDrive (in your home org)
  2. Right-click the file in OneDrive, “Copy share link”
  3. Ensure the link works for external people (check permissions)
  4. Paste the link into the Teams chat

Always works, because your home OneDrive belongs to you.

Workaround 2: channel instead of chat

If the guest tenant set up a team with channels for you:

  1. Go to the matching channel of the foreign team
  2. Upload files directly in the channel - this lands in the channel’s own SharePoint library

Channel files are usually allowed for guests because they do not touch individual OneDrives.

Fix 3: ask the guest tenant admin

The tenant admin of the foreign organization can enable external sharing:

  • Microsoft 365 Admin Center → SharePoint → Sharing → External Sharing: “Anyone” or “New and existing guests”
  • Teams Admin Center → External Access / Guest Access → enable file sharing

This is an org-wide IT decision and often deliberately off in compliance-strict orgs.

If you host guests yourself

Symmetrically: if a guest in your org cannot share files, you as IT can either loosen the sharing policy or offer a channel with a shared files area.