The Tag Messages by Subject feature in Promodag Reports allows administrators to filter and hide messages from traffic reports based on keywords without deleting them from the database. This is useful for excluding automatic messages, private communications, or confidential content from reports distributed across the organization, particularly for GDPR compliance. Users can add predefined or custom tags (like "private," "birthday," or notification keywords), organize them into categories (e.g., notifications, private messages, automatic messages), and easily process or restore them in the database as needed.