As we all know too well, many mails we receive are undesired for various reasons. Sometimes, we just do not want to be part of a scam, sometimes we really prefer no to have this latest joke mail sent by our beloved friends -- even though we are happy to exchange serious messages with them. Sisyphus analyzes each mail in the inbox and the junk folder and uses its subject and text to improve the learning algorithm. Whenever a new mail arrives in the Maildir/new directory, Sisyphus classifies this mail based on its content. Junk mails are then moved automatically to the Maildir/.Junk directory, while good mails are left untouched. See the following blog post on a rather non-technical explanation.