The file sharing permission is limited to the following configuration in the File Sharing and Downloads:
Allow File Sharing: When false, disables file sharing on the server. All file and image uploads on messages are forbidden across clients and devices, including mobile.
Allow File Uploads on Mobile (E20 only): When false, disables file uploads on mobile apps. All file and image uploads on messages are forbidden across clients and devices, including mobile.
Allow File Downloads on Mobile (E20 only): When false, disables file downloads on mobile apps. Users can still download files from a mobile web browser.
To answer the question that you have here:
Only allow upload or download via app - Limited to mobile app on E20
Restrict via web browser from uploading and or downloading - Limited to mobile app on E20
Restrict by user - Not available
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