Any Samsung Knox 2.0+ mobile device using the default native email client
Knox email notifications do not show any content, even if device notifications are enabled to show content on the lock screen. However, Outlook and Gmail notifications will still show content.
By default, content is hidden for Knox Workspace notifications. This is to make sure no one can read, record, or otherwise access the content of email notifications coming from your secure Workspace container.
You can allow or disallow users to change the "Show notification content" setting through your EMM/MDM. Note that not all EMMs/MDMs will allow you to do this.