1.2 Organization of SpamAssassin

At heart, SpamAssassin is a set of modules written in the Perl programming language, along with a Perl script that accepts a message on standard input and checks it using the modules. For higher-performance applications, SpamAssassin also includes a daemonized version of the spam-checker and a client program in C that can accept a message on standard input and check it with the daemon.

Most of SpamAssassin's behavior is controlled through a systemwide configuration file and a set of per-user configuration files. The per- user configuration can also be stored in an SQL database.

For a great deal more about Perl, check out Learning Perl , by Randal L. Schwartz and Tom Phoenix, or Programming Perl , by Larry Wall, Tom Christiansen, and Jon Orwant, both from O'Reilly.