DCC (from http://www.rhyolite.com/anti-spam/dcc/)
DCC (Distributed Checksum Clearinghouse) is a system similar to Razor. It supports fuzzy checksums and therefore detects some more spams than Razor does at the moment.
To install it, perform the following steps:
wget http://www.dcc-servers.net/dcc/source/dcc-dccproc.tar.Z
tar xfvz dcc-dccproc.tar.Z
cd dcc-dccproc-*
./configure && make && make install
You might want to replace the configure call with something like this to get an FHS compliant install:
./configure \
--bindir=$(PREFIX)/bin \
--libexecdir=$(PREFIX)/lib/dcc \
--mandir=$(PREFIX)/man \
--homedir=/var/lib/dcc
Finally call cdcc:
cdcc info
The last command will give some output. The output should contain lines like this:
dcc1.dcc-servers.net,- RTT+0 ms anon
dcc2.dcc-servers.net,- RTT+0 ms anon
...
There should be *at least one*, preferably more than half a dozen, of the public DCC servers listed. If this is not the case, a likely cause is an interfering firewall (see below).
Note that MIMEDefang users may need to set the 'dcc_path' configuration setting, since MIMEDefang does not set a PATH by default. See also 'perldoc Mail::SpamAssassin::Conf'.
Also note that DCC requires that you open your firewall for DCC reply packets on UDP port 6277. DCC uses UDP packets when replying, which are blocked by most firewalls by default. As a result, it requires that you open your firewall for DCC reply packets on UDP port 6277. Here's sample firewall rules required:
allow udp local gt 1023 to remote 6277 allow udp remote 6277 to local gt 1023
If you're running a large site, processing upwards of tens of thousands of messages a day, the DCC maintainers have requested that you consider setting up your own DCC server as described in dccd(8), and arrange to peer with the rest of the public servers, to reduce their load.
More info is at UsingDcc.