How do spam filters know which messages are spam?
Users tell them. With many email systems, such as AOL and Comcast.Net, the recipient of an unwanted message can just click a “Report As Spam” button indicating they do not want the message or others like it. Future messages with similar characteristics will be filtered out. The result is that the more you send email to people who do not want it, the more messages like yours get filtered out by everyone’s spam filters. Also, Internet addresses that are the source of large amounts of email that users consider to be spam are often categorically blacklisted by email services.
