Unlike standard DOX features, Use Mail feature does not focus on the file sharing.
Instead, the main goal is to send the file in one-to-one or one-to-many manners.
Therefore, only the sender or the recipient of the mail can access the file uploaded via Use Mail feature.

Meanwhile, Mail Administrators can view all mails and their file attachments even if they are not the original sender or do not know the URL.

Selecting “Valid Mail for all users” or “Invalid Mail for all users” tab displays the mail list for all users.