A device for blocking unsolicited junk email, known as spam. Spam filters can be set up at the network level, so that junk email is blocked from entering a local network, or else at the individual computer level, so that junk emails are sorted out into a separate junk email folder. Spam filters involve a security level trade-off; the goal is to block all unsolicited email without accidentally filtering out email from legitimate senders. Internet service providers and spam filter software vendors have devised clever algorithms to do this sorting for you, or else allow you to tweak and customize the filters to your individual preferences.