Spamassassin's TxRep Reputation and Bayesian filters

TxRep was designed as an enhanced replacement of the AutoWhitelist plugin. TxRep, just like AWL, tracks scores of messages previously received, and adjusts the current message score, either by boosting messages from senders who send ham or penalizing senders who have sent spam previously. This not only treats some senders as if they were whitelisted but also treats spammers as if they were blacklisted. Each message from a particular sender adjusts the historical total score which can change them from a spammer if they send non-spam messages. Senders who are considered non-spammers can become treated as spammers if they send messages which appear to be spam. Simpler told TxRep is a score averaging system. It keeps track of the historical average of a sender, and pushes any subsequent mail towards that average.

• TxRep - Reputation plugin 
• README.txrep
• Bayes Introduction
• README.bayes

I assume that you have a "spamassassin" DB and user as already done in the previous page.

Changelog

• July 16, 2021
  bayes_token.token field changed to binary(5). It was char(5).
• Version 3.4.3 upgrade notes: It was pointed out (tx Tony Fung) that the count column was renamed in v. 3.4.3 of spamassassin, so you should run this query after the upgrade:

ALTER TABLE `txrep` CHANGE `count` `msgcount` INT(11) NOT NULL DEFAULT '0';

Create the DB tables

> mysql -u root -p

USE spamassassin;
CREATE TABLE txrep (
  username varchar(100) NOT NULL default '',
  email varchar(255) NOT NULL default '',
  ip varchar(40) NOT NULL default '',
  msgcount int(11) NOT NULL default '0',
  totscore float NOT NULL default '0',
  signedby varchar(255) NOT NULL default '',
  last_hit timestamp NOT NULL default CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (username,email,signedby,ip),
  KEY last_hit (last_hit)
) ENGINE=InnoDB;

CREATE TABLE bayes_expire (
  id int(11) NOT NULL default '0',
  runtime int(11) NOT NULL default '0',
  KEY bayes_expire_idx1 (id)
) ENGINE=InnoDB;

CREATE TABLE bayes_global_vars (
  variable varchar(30) NOT NULL default '',
  value varchar(200) NOT NULL default '',
  PRIMARY KEY  (variable)
) ENGINE=InnoDB;

INSERT INTO bayes_global_vars VALUES ('VERSION','3');

CREATE TABLE bayes_seen (
  id int(11) NOT NULL default '0',
  msgid varchar(200) binary NOT NULL default '',
  flag char(1) NOT NULL default '',
  PRIMARY KEY  (id,msgid)
) ENGINE=InnoDB;

CREATE TABLE bayes_token (
  id int(11) NOT NULL default '0',
  token binary(5) NOT NULL default '',
  spam_count int(11) NOT NULL default '0',
  ham_count int(11) NOT NULL default '0',
  atime int(11) NOT NULL default '0',
  PRIMARY KEY  (id, token),
  INDEX bayes_token_idx1 (id, atime)
) ENGINE=InnoDB;

CREATE TABLE bayes_vars (
  id int(11) NOT NULL AUTO_INCREMENT,
  username varchar(200) NOT NULL default '',
  spam_count int(11) NOT NULL default '0',
  ham_count int(11) NOT NULL default '0',
  token_count int(11) NOT NULL default '0',
  last_expire int(11) NOT NULL default '0',
  last_atime_delta int(11) NOT NULL default '0',
  last_expire_reduce int(11) NOT NULL default '0',
  oldest_token_age int(11) NOT NULL default '2147483647',
  newest_token_age int(11) NOT NULL default '0',
  PRIMARY KEY  (id),
  UNIQUE bayes_vars_idx1 (username)
) ENGINE=InnoDB;

Configure

Load TxRep editing v341.pre

# TxRep - Reputation database that replaces AWL 
loadplugin Mail::SpamAssassin::Plugin::TxRep

and commenting out this line in the /etc/mail/spamassassin/v310.pre file:

# loadplugin Mail::SpamAssassin::Plugin::AWL

Configure TxRep and Bayes editing the config file /etc/mail/spamassassin/90-sql.cf:

# spamassassin MySQL user pwd
MYSQL_PWD=xxxxxxx
cat >> /etc/mail/spamassassin/90-sql.cf << __EOF__

# txrep
use_txrep 1
# txrep_autolearn 2
txrep_factory                   Mail::SpamAssassin::SQLBasedAddrList
user_awl_dsn                    DBI:mysql:spamassassin:localhost
user_awl_sql_username           spamassassin
user_awl_sql_password           ${MYSQL_PWD}
user_awl_sql_table              txrep

# bayesian
use_bayes 1
bayes_auto_learn 1
bayes_store_module              Mail::SpamAssassin::BayesStore::MySQL
bayes_sql_dsn                   DBI:mysql:spamassassin:localhost
bayes_sql_username              spamassassin
bayes_sql_password              ${MYSQL_PWD}
# score BAYES_99  4.5 
# score BAYES_999 0.5
__EOF__

You will find that, once your bayesian system has been properly trained, it will be very effective to the point that a great deal of confidence can be assigned to it, so you may want  to increase its spam score, which is 3.5 for spam probability from 99 to 100% and 0.2 for spam probability from 99.9 to 100% (the above scores are added each other). For example you can put this in your local.cf:

score BAYES_99  4.5 
score BAYES_999 0.5

Testing

In order to test the learning system save a raw spam message into a file named spam.txt and run sa-learn in this way (supposing that postmaster@yourdomain.tld is the email recipient)

sa-learn --debug --spam -upostmaster@yourdomain.tld spam.txt

Training Bayes

• More info here

The bayesian classifier can only score new messages if it already has 200 known spams and 200 known hams. So it is the time to train our learning system. Prepare a folder where you have a lot of messages that you are sure are only spam (at least 200 spam messages) and another with only ham.

Then run sa-learn. For a mailbox with spam:

sa-learn --showdots --spam spam-directory/*

For a mailbox with ham:

sa-learn --showdots --ham ham-directory/*

It is important to do both.

Purging the txrep table

The txrep table is going to grow day after day depending on the traffic on your mail server. Most of the records are single spam event that will rarely produce another hit so that you can decide to clean out them to optimize the volume of data stored in that table and speed up the mysql query consequently.

Thus, let's create a file which stores the MySQL query. Modify this example entering the MySQL executable and the spamassassin MySQL account:

# spamassassin MySQL user pwd
MYSQL_PWD=xxxxxxx

cat > /usr/local/bin/txrep_purge.sh << __EOF__ 
#!/bin/sh 
/usr/bin/mysql -u spamassassin -p"${MYSQL_PWD}" -e "USE spamassassin; DELETE FROM txrep WHERE last_hit <= (now() - INTERVAL 120 day);" 
exit 0 
__EOF__

chown root:mysql /usr/local/bin/txrep_purge.sh 
chmod ug+x /usr/local/bin/txrep_purge.sh 
chmod o-rwx /usr/local/bin/txrep_purge.sh

So "spamassassin" is the myql user and "sa_pwd" is the password (this account must have the priviledges for the "spamassassin" DB both from the mail server's IP, from the apache's IP (userprefs via Roundcube) and now from the mysql host (localhost). Don't add spaces after -p.

Finally add the cronjob:

cat >> /etc/cron.d/qmail << __EOF__ 
# txrep
1 1 25 * * /usr/local/bin/txrep_purge.sh >> /var/log/cron
__EOF__

Thu Jul 15 23:21:07 2021 [1447790] dbg: bayes: _put_tokens: SQL error: Incorrect string value: '\xBE\x82]\x05\x96' for column `spamassassin`.`bayes_token`.`token` at row 1
Thu Jul 15 23:21:07 2021 [1447790] dbg: bayes: _put_tokens: SQL error: Incorrect string value: '\xFE\xE9\x99\xF0' for column `spamassassin`.`bayes_token`.`token` at row 1
Thu Jul 15 23:21:07 2021 [1447790] dbg: bayes: _put_tokens: SQL error: Incorrect string value: '\xCA\xDE\xA3' for column `spamassassin`.`bayes_token`.`token` at row 1
Thu Jul 15 23:21:07 2021 [1447790] dbg: bayes: _put_tokens: SQL error: Incorrect string value: '\xFB\x07' for column `spamassassin`.`bayes_token`.`token` at row 1

May 27 01:09:53 mail spamd[10301]: config: failed to parse line, skipping, in "/etc/mail/spamassassin/sql.cf": auto_whitelist_factory Mail::SpamAssassin::SQLBasedAddrList

#auto_whitelist_factory          Mail::SpamAssassin::SQLBasedAddrList

auto_whitelist_factory          Mail::SpamAssassin::SQLBasedAddrList

txrep_factory          Mail::SpamAssassin::SQLBasedAddrList

and commenting out this line:

loadplugin Mail::SpamAssassin::Plugin::AWL

and commenting out this line in the /etc/mail/spamassassin/v310.pre file:

loadplugin Mail::SpamAssassin::Plugin::AWL

CREATE TABLE txrep (
  username varchar(100) NOT NULL default '',
  email varchar(255) NOT NULL default '',
  ip varchar(40) NOT NULL default '',
  msgcount int(11) NOT NULL default '0',
  totscore float NOT NULL default '0',
  signedby varchar(255) NOT NULL default '',
  last_hit timestamp NOT NULL default CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (username,email,signedby,ip),
  KEY last_hit (last_hit)
) ENGINE=InnoDB;

ALTER TABLE `txrep` CHANGE `count` `msgcount` INT(11) NOT NULL DEFAULT '0';

SQL error: Unknown column 'msgcount' in 'field list'

ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,

echo -e 'USE spamassassin;
DELETE FROM awl WHERE ts < (NOW()-(28*24*3600));' | mysql -uspamassassin -pPASSWORD

DELETE FROM awl WHERE ts < (NOW() - INTERVAL 28 DAY)

Mon Jan 17 21:14:27 2011 [5769] info: config: failed to parse line, skipping, in "(no file)": bayes_auto_learn_threshold_spa 10
Mon Jan 17 21:14:27 2011 [5769] info: config: failed to parse line, skipping, in "(no file)": bayes_auto_learn_threshold_spa 10
Mon Jan 17 21:14:27 2011 [5769] info: spamd: processing message <4D34A31D.7050002@domain.xyz for user@domain.xyz:5002
Mon Jan 17 21:14:27 2011 [5769] info: spamd: identified spam (99.3/4.0) for user@domain.xyz:5002 in 0.0 seconds, 1226 bytes.