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Spam Reporting ​

Note

This page describes the recommended way of implementing spam/ham reporting within Dovecot.

This is not the only possible solution, but matches the behavior of many clients and is entirely self-contained within the server.

Spam/not-spam reporting within Dovecot (IMAP) can be handled by the user action of moving a message into (or out of) a defined Spam mailbox.

Configuration ​

Spam reporting messages are handled via imap-sieve plugin. A global configuration script is used to capture the event of moving messages in/out of the Spam mailbox.

WARNING

You cannot run scripts anywhere you want.

Sieve allows you to only run scripts under sieve_pipe_bin_dir. You can't use /usr/local/bin/my-sieve-filter.sh, you have to put the script under sieve_pipe_bin_dir and use my-sieve-filter.sh in the script instead.

The Spam mailbox is defined and reported to the MUA via a Special-Use flag.

External Reporting ​

In this setup, the sieve scripts the script send the reported message using RFC 5965 compliant spam reporting format to an external reporting e-mail address, using the report extension.

Configuration ​

# Display \Junk special-flag for Spam mailbox
namespace inbox {
  mailbox Spam {
    auto = create
    special_use = \Junk
  }
}

# Setup actions based on message movement
protocol imap {
  mail_plugins = $mail_plugins imap_sieve
}
   
plugin {
  sieve_plugins = sieve_imapsieve
  sieve_implicit_extensions = +vnd.dovecot.report
   
  # From elsewhere to Spam folder
  imapsieve_mailbox1_name = Spam
  imapsieve_mailbox1_causes = COPY
  imapsieve_mailbox1_before = file:/etc/dovecot/report-spam.sieve

  # From Spam folder to elsewhere
  imapsieve_mailbox2_name = *
  imapsieve_mailbox2_from = Spam
  imapsieve_mailbox2_causes = COPY
  imapsieve_mailbox2_before = file:/etc/dovecot/report-ham.sieve
}
   
# Needed to send message to external mail server
submission_host = 127.0.0.1:587
require "vnd.dovecot.report";
   
report "abuse" "User added this message to the Spam folder." "spam-report@example.com";
require "vnd.dovecot.report";
require "environment";
require "imapsieve";
   
if environment "imap.mailbox" "Trash" {
  # Putting spam in Trash mailbox is not significant
  stop;
}
   
if environment "imap.mailbox" "Spam" {
  # Copying mail inside Spam mailbox is not significant
  stop;
}
   
report "not-spam" "User removed this message from the Spam folder." "ham-report@example.com";

Local Reporting ​

In this setup, the sieve scripts pass the reported message to local binaries to do classification.

Caveats and Possible Pitfalls ​

  • INBOX name is case-sensitive

  • imap-sieve plugin will only apply to IMAP. It will not apply to LDA or LMTP. Use Sieve normally for LDA/LMTP.

  • With this configuration, moving mails will slow down due to learn being done per email. If you want to avoid this, you need to think of something else. Probably piping things into a FIFO or perhaps using a socket based worker might work better.

  • Please read Sieve and Sieve configuration to understand sieve configuration better.

  • Please read Sieve plugins for more information about sieve extensions.

  • If you run Spamassassin trough Amavis and you use a virtual users setup, you should instead configure Spamassassin to use MySQL/PostgreSQL as a backend, unless you want a headache with file permissions and lock files.

    See: https://docs.iredmail.org/store.spamassassin.bayes.in.sql.html.

    In this case, the -u parameter passed to sa-learn (and the relevant sieve variables) is obsolete and can be safely removed.

  • Reloading Dovecot doesn't activate changes in this configuration, you'll need to perform a full restart.

Configuration ​

# Display \Junk special-flag for Spam mailbox
namespace inbox {
  mailbox Spam {
    auto = create
    special_use = \Junk
  }
}

# Setup actions based on message movement
protocol imap {
  mail_plugins = $mail_plugins imap_sieve
}
   
plugin {
  sieve_plugins = sieve_imapsieve
  sieve_implicit_extensions = +vnd.dovecot.report
   
  # From elsewhere to Spam folder
  imapsieve_mailbox1_name = Spam
  imapsieve_mailbox1_causes = COPY
  imapsieve_mailbox1_before = file:/etc/dovecot/report-spam.sieve

  # From Spam folder to elsewhere
  imapsieve_mailbox2_name = *
  imapsieve_mailbox2_from = Spam
  imapsieve_mailbox2_causes = COPY
  imapsieve_mailbox2_before = file:/etc/dovecot/report-ham.sieve

  sieve_pipe_bin_dir = /usr/lib/dovecot/sieve
  sieve_global_extensions = +vnd.dovecot.pipe +vnd.dovecot.environment
}
require ["vnd.dovecot.pipe", "copy", "imapsieve", "environment", "variables"];

if environment :matches "imap.user" "*" {
  set "username" "${1}";
}

# "sa-learn-spam.sh" MUST live in /usr/lib/dovecot/sieve
pipe :copy "sa-learn-spam.sh" [ "${username}" ];
require ["vnd.dovecot.pipe", "copy", "imapsieve", "environment", "variables"];

if environment :matches "imap.mailbox" "*" {
  set "mailbox" "${1}";
}

if string "${mailbox}" "Trash" {
  stop;
}

if environment :matches "imap.user" "*" {
  set "username" "${1}";
}

# "sa-learn-ham.sh" MUST live in /usr/lib/dovecot/sieve
pipe :copy "sa-learn-ham.sh" [ "${username}" ];

Shell Scripts ​

Spamassassin ​

Untested

spamc interaction scripts are not tested yet.

sh
#!/bin/sh
# you can also use tcp/ip here, consult spamc(1)
exec /usr/bin/spamc -u ${1} -L spam
sh
#!/bin/sh
# you can also use tcp/ip here, consult spamc(1)
exec /usr/bin/spamc -u ${1} -L ham

You can also use sa-learn.

Note that using sa-learn often incurs significant start-up time for every message. This can cause "lockout" of the user until all the processes sequentially complete, potentially tens of seconds or minutes. If spamd is being used and the administrator is willing to accept the potential security issues of allowing unauthenticated learning of spam/ham, spamd can be invoked with the --allow-tell option and spamc with the --learntype= option. Please consult the man pages of spamd and spamc for further details.

sh
#!/bin/sh
exec /usr/bin/sa-learn -u ${1} --spam
sh
#!/bin/sh
exec /usr/bin/sa-learn -u ${1} --ham

dspam ​

sh
#!/bin/sh
exec /usr/bin/dspam --client --user ${1} --class=spam --source=error
sh
#!/bin/sh
exec /usr/bin/dspam --client --user ${1} --class=innocent --source=error

CRLF handling

dspam may fail to read the mail if it contains CRLF line endings. Add the Broken lineStripping option in dspam.conf if needed.

rspamd ​

By default, rspamd does global learning. If you want per-user classification, or something more complex, see https://rspamd.com/doc/configuration/statistic.html

Alternative scripts can be found from https://github.com/darix/dovecot-sieve-antispam-rspamd/

sh
#!/bin/sh
exec /usr/bin/rspamc -h /run/rspamd/worker-controller.socket -P <secret> learn_spam
sh
#!/bin/sh
exec /usr/bin/rspamc -h /run/rspamd/worker-controller.socket -P <secret> learn_ham

Before running following commands, make sure dovecot.conf has all the sieve configuration you want. Then run following commands:

console
$ sievec /etc/dovecot/sieve/report-spam.sieve
$ sievec /etc/dovecot/sieve/report-ham.sieve
$ chmod +x /etc/dovecot/sieve/sa-learn-ham.sh /etc/dovecot/sieve/sa-learn-spam.sh

Now your learn scripts should be invoked when you move mails between folders.

Debugging ​

To debug, you need to import "vnd.dovecot.debug" extension. Then you can put in your Sieve script, when required (variables supported):

debug_log "something"

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