SpamAssassin is a neat Email filter that tags incoming mails it thinks are spam. Its aggressiveness can be configured, and it comes with a decent default level. It's written in Perl and is licensed under the same license as Perl itself. You can use procmail(1) to run SpamAssassin, or you might want to use MailScanner to run it on all your incoming mail. You might even want to plug VipulsRazor into it.

(Note, this product will assassinate Spam, but will leave SPAM well alone!)

How to make SpamAssassin run on your local e-mail machine (with Evolution in mind)

• get and install SpamAssassin, test that it works by piping a good email and a spam email through it
• check that fetchmail(1) works, write a .fetchmailrc file
• check that procmail(1) works, write a .procmailrc file
• disable the regular pop mailboxes in Evolution
• add a new "local delivery" mailbox to Evolution
• write a tiny script I called getmail that does fetchmail -m procmail and make sure that it gets your email from the POP3 server correctly
• add getmail to your crontab to run every 5 minutes
• add a filter rule to Evolution: if specific header X-Spam-Flag = YES, drop the email in my Spam folder

.fetchmailrc:

poll mail.myisp.co.nz protocol POP3
      user "pop3user" password "secret" is user "localuser" here mda "/usr/bin/procmail";

.procmailrc:

# correct incoming messages for programs like Evolution and mail
:0 fhw
| formail -I "From " -a "From "

:0fw
| spamassassin

/bin/getmail:

#!/bin/bash
/usr/bin/fetchmail >> ~/log/fetchmail

crontab:

*/5 * * * * /home/localuser/bin/getmail

The ClamAV Plugin

This plugin submits the entire email to a locally running ClamAV server for virus detection. If a virus is found, it returns a positive return code to indicate spam and sets the header X-Spam-Virus: Yes ($virusname). If you'd like to sort virus emails to a separate folder, create a rule looking for this header.

It requires

• ClamAV installed so that scanning a mail with clamscan works
• the File::Scan::ClamAV Perl module

To install, create the files in /etc/mail/spamassassin/. You can adjust the default score of 10 in clamav.cf if you like. Restart the spamd daemon if you're using that, and you should be all set.

clamav.cf:

loadplugin ClamAV clamav.pm
full CLAMAV eval:check_clamav()
describe CLAMAV Clam AntiVirus detected a virus
score CLAMAV 10

clamav.pm:

package ClamAV;
use strict;
use warnings;

use Mail::SpamAssassin;
use Mail::SpamAssassin::Plugin;
use File::Scan::ClamAV;

our @ISA = qw(Mail::SpamAssassin::Plugin);

sub new {
    my ( $class, $mailsa ) = @_;
    my $self = $class->SUPER::new( $mailsa );
    bless( $self, $class );
    $self->register_eval_rule( "check_clamav" );
    return $self;
}

sub _set_header {
    my ( $msgstatus, $header ) = @_;
    $msgstatus->{ main }->{ conf }->{ $_ }->{ "Virus" } = $header
        for qw( headers_spam headers_ham );
}

sub check_clamav {
    my ( $self, $permsgstatus, $fulltext ) = @_;
    my $clamav = File::Scan::ClamAV->new( port => 3310 );
    my ( $code, $virus ) = $clamav->streamscan( ${ $fulltext } );
    if ( !$code ) {
        my $errstr = $clamav->errstr();
        Mail::SpamAssassin::Plugin::dbg( "ClamAV: Error scanning: $errstr" );
        _set_header( $permsgstatus, "Error ($errstr)" );
    }
    elsif ( $code eq 'OK' ) {
        Mail::SpamAssassin::Plugin::dbg( "ClamAV: No virus detected" );
        _set_header( $permsgstatus, "No" );
    }
    elsif ( $code eq 'FOUND' ) {
        Mail::SpamAssassin::Plugin::dbg( "ClamAV: Detected virus: $virus" );
        _set_header( $permsgstatus, "Yes ($virus)" );
        return 1;
    }
    else {
        Mail::SpamAssassin::Plugin::dbg( "ClamAV: Error, unknown return code: $code" );
        _set_header( $permsgstatus, "Error (Unknown return code from ClamAV: $code)" );
    }
    return;
}
1;

GreigMcGill has found that MaiaMailguard? is an excellent meta tool for managing your anti spam solution.