Sounds interesting, but I thought DCC, like pyzor/razor simply checks message content against known spam databases? How would one use it to detect duplicate messages? Any idea?
Technicaly, DCC does not detect the "spamminess" of a message, it's just how common a message is, with no consideration if it's common because it is spam vs common nonspam. Whitelists are used to reduce some obvious nonspam hits, but in general DCC does occasionally fire off on high-volume nonspam mailings, such as vendor announcements from Intel... (Then again, despite it's claims of being spam only, razor seems to FP much more often in the past couple years that I've been using both)
Every non-whitelisted message that goes into the DCC client for check is also is reported to the DCC server by default. You actually need to pass a parameter to dccproc in order for it to NOT report the message.
The server provides a count of messages with the same hash.
All you need to do is run a local DCC server and configure the DCC client to have a pretty low count threshold and you'll be detecting duplicate messages.
