SpamSieve works with your e-mail program to filter out spam messages. First, the mail program downloads new messages from the mail server. It then passes the messages to a plug-in or AppleScript, which in turn passes them to the SpamSieve application. SpamSieve analyzes the messages to see whether they are spam. It returns the verdict to the plug-in or script, which then directs the mail program to move the messages to another folder.