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Grunt’s Send feature relies on the Windows mail handoff used by Outlook. The legacy support guidance notes a specific limitation in Outlook (new) on Windows.

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What the problem looks like

When you use Send in Grunt:
  • An email draft appears to be generated
  • The attachment may be present
  • The recipient never receives the email
  • The email does not appear in Sent Items
  • No clear error message is shown

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Why it happens

According to the legacy support article, Outlook (new) does not support the same attachment-based email generation flow that Grunt depends on. Windows therefore needs the fallback path through Outlook (classic) for attachment-based sends.

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Fix on Windows 10

  1. Open Outlook (classic) once.
  2. Close it again.
  3. Open Settings > Apps > Default apps > Choose default apps by protocol.
  4. Find MAILTO.
  5. If it currently points to Outlook (new), switch it to Outlook (classic).
  6. Then switch it back to Outlook (new).
This repair step helps Windows restore the correct fallback behavior.

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Fix on Windows 11

  1. Open Outlook (classic) once.
  2. Close it again.
  3. Open Settings > Apps > Default apps.
  4. Search for MAILTO.
  5. Open the URL:MailTo Protocol entry.
  6. If it currently points to Outlook (new), switch it to Outlook (classic).
  7. Then switch it back to Outlook (new).

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Expected result

After this change:
  • Emails with attachments created by Grunt should open through Outlook (classic)
  • Regular mail links without attachments can still open in Outlook (new)
If email handoff is still blocked in your environment, export the file manually and attach it yourself from Outlook.