Twilio automatically stores all media files to your project that are sent or received with our long codes and shortcodes. These files are saved to your project with a unique Media Instance Resource. Users looking to enhance their media file security can enable HTTP Authentication for Media URLs from the General SMS Settings page in Console.
Twilio will continue to store these media files until you make an HTTP DELETE request to the media file's resource. For more information on deleting media resources, including code samples, see Delete a Media resource (Twilio docs).