For my own reference, after few hours messing around with shit called mail system.

Packages:

• postfix
• dovecot-imapd (from backports)
• dovecot-managesieved (from backports)
• dovecot-sieve (from backports)
• amavisd-new
• spamassassin

Basic configuration as laid out from my previous post about mail.

And this is the continuation: spam filter and also sieve (which used to automatically filter mails based on rules).

Postfix

In /etc/postfix/master.cf:

127.0.0.1:10025 inet    n       -       y       -       -       smtpd
        -o content_filter=
        -o local_recipient_maps=
        -o relay_recipient_maps=
        -o smtpd_restriction_classes=
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=permit_mynetworks,reject
        -o mynetworks=127.0.0.0/8
        -o strict_rfc821_envelopes=yes
smtp-amavis     unix    -       -       y       -       1       smtp
        -o smtp_data_done_timeout=1200
        -o disable_dns_lookups=yes

And then in /etc/postfix/main.cf:

content_filter=smtp-amavis:[127.0.0.1]:10024

[ Reference ]

SpamAssassin

Nothing to configure here AFAIR.

Amavis side

Uncomment following lines in /etc/amavis/conf.d/15-content_filter_mode:

@bypass_spam_checks_maps = (
%bypass_spam_checks, @bypass_spam_checks_acl, $bypass_spam_checks_re);

And add following line to /etc/amavis/conf.d/50-user:

$sa_spam_subject_tag = '';

(No reference for this one as I figured this out by myself)

Dovecot

Add sieve and autocreate plugin in /etc/dovecot/conf.d/15-lda.conf:

protocol lda {
  mail_plugins = $mail_plugins sieve autocreate
}

Configure the autocreate plugin in /etc/dovecot/conf.d/90-plugin.conf:

plugin {
  autocreate = Junk
  autosubscribe = Junk
}

Create the spam filter in /etc/dovecot/sieve/spam.sieve:

require "fileinto";
if header :contains "X-Spam-Flag" "YES" {
  fileinto "Junk";
}

…and compile it using sievec:

# sievec /etc/dovecot/sieve/spam.sieve

…and finally add it as global filter in /etc/dovecot/conf.d/90-sieve.conf:

plugin {
  ...
  sieve_global_dir = /etc/dovecot/sieve
  sieve_before = /etc/dovecot/sieve

[ Reference ]

And done (I think).