DCC Distributed Checksum Clearinghouse
So what is the meaning of DCC. DCC stands for Distributed Checksum Clearinghouse and is a function thar can be used to make a mathematical checksum of the e-mail. This checksum is sent to participants in DCC. If a e-mail/checksum has been seen enough times on the network then it can be classified as a spam e-mail.
A checksum is a mathematical formula that can take a text and make it to for example a 128 bits string. So for example the Moby Dick book will be calculated down to a 128 bit string. If one character in Moby Dick is changed then the checksum will not be the same checksum as before.