Distributed Checksum Clearinghouse (also referred to as DCC) is a method of spam email detection.
The basic logic in DCC is that most spam mails are sent to many recipients.
The same message body appearing many times is therefore bulk email.
According to the official DCC website: The DCC is based on an idea of Paul Vixie and on fuzzy body matching to reject spam on a corporate firewall operated by Vernon Schryver starting in 1997.
The DCC was designed and written at Rhyolite Software starting in 2000.