New Outlook for Windows fails to attach shared files — "The following files weren't attached because they're empty"

Paul Xu 20 Reputation points
2026-06-17T09:44:09.9866667+00:00

When sharing a PDF file from a web application via the Windows native Share Sheet (invoked through the browser's Web Share API), selecting New Outlook (desktop app) as the share target results in the error: "The following files weren't attached because they're empty: [Moderator Note: Personal Info Removed]". The temporary file created by the Windows Share Contract is 0 bytes despite the original file containing valid data.

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But this issue is specific to the New Outlook desktop app — sharing to Outlook web version works correctly

Outlook | Web | Outlook.com | Email
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Chloe-V 13,360 Reputation points Microsoft External Staff Moderator
2026-06-18T02:54:33+00:00

Hi Paul Xu,

Welcome to Microsoft Q&A forum. 

Based on your test, the PDF file itself seems to be valid, as it can be shared successfully through Outlook on the web. The incident appears to happen only when the file is passed to the New Outlook desktop app through the Windows Share Sheet/Web Share flow.

At the moment, New Outlook for Windows may not handle this type of app-to-mail sharing flow in the same way as classic Outlook. Because of that, the temporary file created during the share process can be detected as empty, even though the original PDF has content.

For now, please try one of these workarounds:

  • Use Outlook on the web when sharing the file directly from the web application.
  • Save the PDF to your device first, then open New Outlook and attach it manually using Attach file.
  • If this sharing workflow is important for your daily work, you may need to use classic Outlook for this specific action for now.

I also suggest sending feedback from New Outlook by going to Help > Feedback and including the screenshots and reproduction steps.

Please note that this is a user-to-user support forum. Moderators, contributors including external Microsoft employees cannot directly intervene in Microsoft product features or access back-end systems. Our role is limited to providing technical guidance on reported issues, requests, or ideas only.

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  1. AI answer

    2026-06-17T09:44:28.63+00:00

    New Outlook for Windows does not fully support all legacy integration paths that classic Outlook supports. In particular, it is not MAPI‑compliant and cannot reliably act as a target for some “share to email” workflows from other apps.

    In this scenario, the Windows Share Sheet creates a temporary file for New Outlook to attach, but because the integration path is not supported, the temp file remains 0 bytes and New Outlook reports it as an empty attachment. This is why the same operation works when targeting Outlook on the web but fails when targeting the New Outlook desktop app.

    There is no configuration change in New Outlook that will fix this behavior today. Practical workarounds are:

    1. Use Outlook on the web as the share target, where the attachment is created correctly.
    2. Save the PDF locally from the web application, then attach it from within New Outlook using the standard Attach flow.
    3. Use classic Outlook for Windows as the default mail client when relying on “share to email” features from other applications, since classic Outlook remains the supported MAPI‑compliant target.

    If this workflow is critical, using classic Outlook instead of New Outlook for now avoids the empty‑file issue until New Outlook adds broader integration support.

    References:

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