A hosted service like Postini is a great thing. It keeps the unwanted traffic off of your network and keeps it clean for business traffic. Postini provides a self-service interface for the user quarantine so the quarantined messages do not have to be stored on your system. That saves in disk space and backup requirements. Postini can also queue e-mail if your network connection is dropped so it can offer some form of business continuity also for e-mail services.