Hello,
The problem is the browser can’t return the correct mime type for msg files.
and this https://stackblitz.com/edit/mime-type-checker?file=index.js
If you are not strict on file extensions for this upload, just leave the “Restrictions” empty and it should work.
Huy
Check it out here https://www.outsystems.com/forums/discussion/69389/how-to-get-right-mime-type-for-msg-file-while-uploading-file/
you can import MSG Files into Outlook 365 easily.