2.1 Prerequisites

SpamAssassin is written for a Unix or Unix-like environment that includes Perl Version 5, preferably 5.6.1 or later. Perl is now standard on most Unix systems, but if you don't have it, the source code for Perl can be downloaded at http://www.cpan.org.

SpamAssassin requires several Perl modules to be installed. If you install SpamAssassin using CPAN (the Comprehensive Perl Archive Network), as described in the next section, these modules will be automatically downloaded and installed as well. If you install SpamAssassin manually, you'll need to be sure that you also have up-to-date versions of the Perl modules ExtUtils::MakeMaker , File::Spec , Pod::Usage , HTML::Parser , Sys::Syslog , DB_File , Digest::SHA1 , and Net::DNS . You may also want Net::Ident and IO::Socket::SSL if you plan to use the daemonized checker ( spamd ) and its client ( spamc ) and you will allow remote clients to access your daemon.

SpamAssassin can consult several spam checksum clearinghouses. A spam clearinghouse is a server (or a distributed network of servers) that gathers spam messages reported by thousands of users around the world and provides a mechanism for a client to check a new message to see if it matches a message in the clearinghouse. These clearinghouses are known as checksum -based clearinghouses because rather than transmit and store complete email messages, they work with cryptographic checksums of messages. A cryptographic checksum is a much smaller data string (typically no more than 256 bits) that is, for all practical purposes, unique to the message from which it is computed.

As of version 3.0, SpamAssassin can consult three clearinghouses: Vipul's Razor (http://razor. sourceforge .net), Pyzor (http://pyzor.sourceforge.net), and DCC (http://www.rhyolite.com/anti-spam/dcc/). SpamAssassin can also be used to report spam to the clearinghouses. Each clearinghouse uses its own client software, and you should install these clients before you install SpamAssassin. In most cases, each SpamAssassin user will have to manually run the clearinghouse's client program to initialize it before SpamAssassin can use it.

In many sitewide SpamAssassin configurations, you will create a dedicated special user account to run SpamAssassin. If you do and you intend to use spam clearinghouses, be sure that you follow the client software instructions for initialization and that you do so as the dedicated user , rather than as root .