DCC is the Distributed Checksum Clearinghouse. http://www.rhyolite.com/anti-spam/dcc/ . DCC is a HashSharingSystem.

Installing DCC

See InstallingDCC.

Enabling DCC

To make SpamAssassin use DCC, uncomment the following line in the v310.pre file so the plugin gets loaded:

loadplugin Mail::SpamAssassin::Plugin::DCC

It is recommended to set explicit configuration in your "local.cf", so things are not relying on PATH etc.

use_dcc 1
# When using dccifd, socket will be search from dcc_home
dcc_home /var/dcc
dcc_timeout 8
# If not using dccifd, dccproc is used
dcc_path /usr/local/bin/dccproc

I've installed DCC but I never seem to get DCC hits, even though I should. Why?

If you have installed DCC, and are running spamassassin or spamd without the "-L" switch, you should be seeing hits in spam reports.

Check your firewall setup. 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. Modern firewalls already track connections and replies, so simply having a standard rule like "iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT" is enough. For more information see: https://www.dcc-servers.net/dcc/FAQ.html#firewall-ports

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.

Detailed instructions

Very detailed instructions on configuring DCC for a personal Unix account are in SingleUserUnixInstall.


Using SpamAssassin to submit spam is described in ReportingSpam.

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