Every DCC server maintains a database of checksums of mail messages. It contains checksums of mail seen locally as well as 30 days of checksums of bulk mail seen by servers in the global network of DCC servers. Each stream of bulk mail generates 1 to 3 checksums. Extra checksums are pruned. Thus, the number of checksums in the database is related to the number of streams of spam in the last 30 days, and the relationship is best when the server receives few client DCC transactions.
See also the other DCC graphs.
These graphs are generated from cdcc stats values collected in RRDTOOL databases. The scripts that collect the data and render the graphs are in the DCC source. The rendering is done with rrdtool graph. All dates and times are in UTC, which is between 3 and 7 hours ahead of time in the U.S.