Drag and Drop Emails from New Outlook into Custom Web Applications

New Outlook for Windows does not expose a dragged message as a file to an arbitrary browser application; for a supported no-local-save workflow, host the integration in an Outlook web add-in or retrieve the message as MIME through Microsoft Graph.

Current support and roadmap status

• Third-party browser upload areas: Directly dragging a whole message from New Outlook into an independent browser window is not currently supported, so DataTransfer.files will not contain the .msg/.eml file your existing upload control expects. This is a client limitation rather than an HTML5 implementation issue in your application.^1^
• File format: New Outlook does not provide classic-style .msg drag-and-drop. Where message drag-and-drop is supported in a New Outlook add-in task pane, messages are delivered as .eml files. Classic Outlook delivers them as .msg.^2^
• Release date: The public information supplied here does not identify a Microsoft 365 Roadmap item or estimated date specifically for dragging whole messages from New Outlook into arbitrary browser applications.
• Roadmap/release-note entries for dragging files between accounts as attachments address an Outlook cross-account compose workflow, not exporting whole messages to third-party browser drop zones.^3^

Supported no-local-save option: Outlook web add-in

Move the upload interface into an Outlook add-in task pane, while keeping your existing web API as the backend. New Outlook and Outlook on the web support message and attachment drops into that task pane through Office.EventType.DragAndDropEvent; dropped messages arrive as .eml data.^2^

A minimal handler is:

Office.context.mailbox.addHandlerAsync(
  Office.EventType.DragAndDropEvent,
  async (event) => {
    const transfer = event.dragAndDropEventData;
    if (transfer.type !== "drop") return;

    for (const file of transfer.dataTransfer.files) {
      await uploadToApplication(file.name, file.fileContent);
    }
  },
  result => {
    if (result.status === Office.AsyncResultStatus.Failed) {
      console.error(result.error.message);
    }
  }
);

Important constraints include:

• The source item and task pane cannot be from another mailbox.
• Dropping a mixture of messages and attachments together is unsupported.
• Moving to another mail item during processing can interrupt an unpinned task pane, so show upload progress and errors.
• This API applies specifically to an Outlook add-in task pane; it does not enable the same event in your existing standalone browser page.^2^

Alternative: retrieve .eml through Microsoft Graph

If users can select a message in your application instead of dragging it, retrieve its MIME representation through Microsoft Graph:

GET /me/messages/{message-id}/$value
Authorization: Bearer {access-token}
Accept: application/octet-stream

The response is the raw MIME content and can be stored or uploaded as an .eml file. The application must obtain the appropriate permission to access the message.^4^

This avoids writing a temporary file to the user’s computer, but it requires Microsoft Entra authentication, mailbox permissions, and a way to identify the selected message.

Remaining operational choices

If redesigning as an add-in or Graph integration is not currently feasible:

1. Keep affected users on Classic Outlook, which continues to provide the browser drag workflow as .msg.
2. In New Outlook, save or drag the message to a local folder as .eml, then upload it. This is the practical two-step workaround, but it does not satisfy the no-local-save requirement.^5^
3. Submit the precise scenario through Help → Give Feedback in New Outlook. Microsoft’s feature comparison directs feature requests there, but it does not commit to a delivery date.^6^

References

1. In new Outlook, unable to Drag and drop emails to web browser.
2. Drag and drop messages and attachments into the task pane of an Outlook add-in
3. Release notes for Outlook for Windows (new)
4. Get MIME content of a message
5. Drag and Drop Email from New Outlook to Web File Upload Dialog Not Working - Microsoft Q&A
6. Feature comparison between new Outlook and classic Outlook