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I have a problem with Outlook 365 add-in we are developing. The add-in should accept files dragged from user desktop. The web page is working fine with Drag&Drop in any browser: IE, Edge, Opera.

Same web page in add-in accepts only files dragged from Office 365 Application and doesn't accept anything from Outlook, user desktop, any other website or app.

So in fact add-in is droppable and working fine, but only for files dragged from Office 365 App.

Is there any special security setting in place?

Alex Z
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  • See https://stackoverflow.com/questions/17184369/upload-fails-when-user-drags-and-drops-attachment-from-email-client/17197224#17197224 – Dmitry Streblechenko Apr 01 '21 at 23:51
  • Does this answer your question? [Upload fails when user drags and drops attachment from email client](https://stackoverflow.com/questions/17184369/upload-fails-when-user-drags-and-drops-attachment-from-email-client) – EricSchaefer Apr 04 '21 at 12:41

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The web browser which hosts your web add-in doesn't recognize and understand the format which is used for dragged items from Outlook. On the page Upload fails when user drags and drops attachment from email client you may find the following explanation:

All browsers are only expecting the actual file drag/drop format (CF_HDROP), but when dragging from Outlook, there is no file on the filesystem. What you get is the CF_FILEDESCRIPTOR and CF_FILECONTENTS formats. No browser that I know of (not even IE), knows how to handle that.

Eugene Astafiev
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  • The problem is that the browser (Edge) which hosts the add-in doesn't accept DROPS from anything (even file explorer) except links dragged from Office365 application. – Alex Z Apr 03 '21 at 08:47