How does PenaltyBox reduce spam?

PenaltyBox checks mail sent from outside the University to uniqname@umich.edu and groupname@umich.edu addresses for two characteristics:

Compliance with Internet and e-mail system best practices and protocols.
Whether the connecting IP address (the address from which the mail is sent) is included on the Do Not Spam List and other such lists of known spammers.

PenaltyBox then causes a temporary delivery failure to be generated for mail that it considers questionable. PenaltyBox stores information about the mail, and, if delivery is retried, the mail is accepted. (See diagram showing what PenaltyBox does.)

PenaltyBox takes advantage of the fact that spambots and compromised spam-sending machines seldom queue and resend mail that doesn't get through the first time. Legitimate Internet Service Providers, however, routinely queue and resend mail messages that encounter temporary delivery failures.

For technical details about PenaltyBox, see the PenaltyBox web page. Please note that PenaltyBox only works on mail that enters the University through the mail gateway.

PenaltyBox works in concert with the other anti-spam services provided by ITS to provide a comprehensive approach to fighting spam. A diagram showing where in the e-mail delivery process each of these services works is on the ITS website. (Comprehensive Anti-Spam Services diagram)

Return to the Spam FAQ