This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.

Pigeonhole Sieve: Spamtest and Virustest Extensions

Using the spamtest and virustest extensions (RFC 5235), the Sieve language provides a uniform and standardized command interface for evaluating spam and virus tests performed on the message. Users no longer need to know what headers need to be checked and how the scanner's verdict is represented in the header field value. They only need to know how to use the spamtest (spamtestplus) and virustest extensions. This also gives GUI-based Sieve editors the means to provide a portable and easy to install interface for spam and virus filter configuration. The burden of specifying which headers need to be checked and how the scanner output is represented falls onto the Sieve administrator.

Configuration

The spamtest, spamtestplus and virustest extensions are not enabled by default and thus need to be enabled explicitly using the sieve_extensions setting.

The following settings need to be configured for using the spamtest and spamtestplus extensions. The virustest extension has identical configuration settings, but with a 'sieve_virustest_' prefix instead of a 'sieve_spamtest_' prefix:

sieve_spamtest_status_type = "score" / "strlen" / "text"

This specifies the type of status result that the spam/virus scanner produces. This can either be a numeric score (score), a string of identical characters (strlen), e.g. '*******', or a textual description (text), e.g. {{{Spam}}}'  or Not Spam'.

sieve_spamtest_status_header = <header-field> [ ":" <regexp> ]
This specifies the header field that contains the result information of the spam scanner and it may express the syntax of the content of the header. If no matching header is found in the message, the spamtest command will match against "0".

This is a structured setting. The first part specifies the header field name. Optionally, a POSIX regular expression follows the header field name, separated by a colon. Any white space directly following the colon is not part of the regular expression. If the regular expression is omitted, any header content is accepted and the full header value is used. When a regular expression is used, it must specify one match value (inside brackets) that yields the desired spam scanner result. If the header does not match the regular expression or if no value match is found, the spamtest test will match against "0" during Sieve script execution.

sieve_spamtest_max_value =
This statically specifies the maximum value a numeric spam score can have.
sieve_spamtest_max_header = <header-field> [ ":" <regexp> ]

Some spam scanners include the maximum score value in one of their status headers. Using this setting, this maximum can be extracted from the message itself in stead of specifying the maximum manually using the setting sieve_spamtest_max_value explained above. The syntax is identical to the sieve_spamtext_status_header setting.

sieve_spamtest_text_valueX =

When the sieve_spamtest_status_type setting is set to text, these settings specify that the spamtest test will match against the value "X" when the specified string is equal to the text (extracted) from the status header. For spamtest and spamtestplus, values of X between 0 and 10 are recognized, while virustest only uses values between 0 and 5.

Examples

This section shows several configuration examples. Each example shows a specimen of valid virus/spam test headers that the given configuration will work on.

Example 1

Spam header: X-Spam-Score: No, score=-3.2

plugin {
  sieve_extensions = +spamtest +spamtestplus

  sieve_spamtest_status_type = score
  sieve_spamtest_status_header = \
    X-Spam-Score: [[:alnum:]]+, score=(-?[[:digit:]]+\.[[:digit:]])
  sieve_spamtest_max_value = 5.0
}

Example 2

Spam header: X-Spam-Status: Yes

plugin {
  sieve_extensions = +spamtest +spamtestplus

  sieve_spamtest_status_type = text
  sieve_spamtest_status_header = X-Spam-Status
  sieve_spamtest_text_value1 = No
  sieve_spamtest_text_value10 = Yes
}

Example 3

Spam header: X-Spam-Score: sssssss

plugin {
  sieve_extensions = +spamtest +spamtestplus

  sieve_spamtest_status_header = X-Spam-Score
  sieve_spamtest_status_type = strlen
  sieve_spamtest_max_value = 5
}

Example 4

Spam header: X-Spam-Score: status=3.2 required=5.0

Virus header: X-Virus-Scan: Found to be clean.

plugin {
  sieve_extensions = +spamtest +spamtestplus +virustest

  sieve_spamtest_status_type = score
  sieve_spamtest_status_header = \
    X-Spam-Score: score=(-?[[:digit:]]+\.[[:digit:]]).*
  sieve_spamtest_max_header = \
   X-Spam-Score: score=-?[[:digit:]]+\.[[:digit:]] required=([[:digit:]]+\.[[:digit:]])

  sieve_virustest_status_type = text
  sieve_virustest_status_header = X-Virus-Scan: Found to be (.+)\.
  sieve_virustest_text_value1 = clean
  sieve_virustest_text_value5 = infected
}

Pigeonhole/Sieve/Extensions/SpamtestVirustest (last edited 2011-04-14 22:43:26 by Stephan Bosch)