@c This is part of the GNU Mailutils manual.
@c Copyright (C) 1999-2004, 2007-2008, 2010-2012, 2014-2017 Free
@c Software Foundation, Inc.
@c See file mailutils.texi for copying conditions.
@comment *******************************************************************

The input language understood by the GNU Sieve Library
is a superset of the Sieve language as described in RFC 3028.

@menu
* Lexical Structure::
* Syntax::
* Preprocessor::
* Require Statement::
* Comparators::
* Tests::
* Actions::
* Extensions::
* GNU Extensions::
@end menu

@node Lexical Structure
@section Lexical Structure

@subheading Whitespace and Comments

Comments are semantically equivalent to whitespace and can be used
anyplace that whitespace is (with one exception in multi-line strings,
as described below).

There are two kinds of comments: hash comments, that begin with a
@samp{#} character that is not contained within a string and continue
until the next newline, and C-style or bracketed comments, that are
delimited by @samp{/*} and @samp{*/} tokens.  The bracketed comments
may span multiple lines.  E.g.:

@smallexample
if size :over 100K
  @{ # this is a comment
    discard;
  @}
  
if size :over 100K
  @{ /* this is a comment
       this is still a comment */ discard /* this is a comment again
     */ ;
  @}
@end smallexample

Like in C, bracketed comments do not nest.

@subheading Lexical Tokens

The basic lexical entities are @dfn{identifiers} and @dfn{literals}.

An @dfn{identifier} is a sequence of letters, digits and underscores,
that begins with a letter or underscore.  For example, @code{header} and
@code{check_822_again} are valid identifiers, whereas @code{1st} is not.
A special form of identifier is @dfn{tag}: it is an identifier prefixed
with a colon (@samp{:}), e.g.: @code{:comparator}. 

A @dfn{literal} is a data that is not executed, merely evaluated ``as
is'', to be used as arguments to commands.  There are four kinds of
literals:

@itemize
@item Number
@cindex numbers, sieve

@dfn{Numbers} are given as ordinary unsigned decimal numbers.  An
optional suffix may be used to indicate a multiple of a power of two.
The suffixes are: @samp{K} specifying ``kibi-'', or 1,024 (2^10) times
the value of the number; @samp{M} specifying ``mebi-'', or 1,048,576
(2^20) times the value of the number; and @samp{G} specifying ``tebi-'',
or 1,073,741,824 (2^30) times the value of the number.

The numbers have 32 bits of magnitude.

@item String
@cindex strings, sieve
A @dfn{string} is any sequence of characters enclosed in double quotes
(@samp{"}).  A string cannot contain newlines and double quote
characters.  This limitation will disappear in future releases.

@item Multiline Strings
@cindex multiline strings, sieve
@kwindex text:
A @dfn{multiline string} is used to represent large blocks of text
with embedded newlines and special characters.  It starts with the
keyword @code{text:} followed by a newline and ends with a dot
(@samp{.}) on a newline by itself.  Any characters between these two
markers are taken verbatim.  For example:

@smallexample
text:
** This is an automatic response from my message **
** filtering program.                            **

I can not attend your message right now.  However it
will be saved, and I will read it as soon as I am back.

Regards,
Fred
.
@end smallexample

Notice that a hashed comment or whitespace may occur between
@code{text:} and the newline.  However, when used inside the multiline
string a hash sign looses its special meaning (except in one case, see
below) and is taken as is, as well as bracketed comment delimiters.
In other words, no comments are allowed within a multiline string.  E.g.:
    
@smallexample
text: # This is a comment

Sample text
# This line is taken verbatim
/* And this line too */
.
@end smallexample

The only exception to this rule is that preprocessor @code{include}
statement is expanded as usual when found within a multiline string
(@pxref{Preprocessor}), e.g.:

@smallexample
text:
#include <myresponse.txt>
.
@end smallexample

This results in the contents of file @file{myresponse.txt} being read
and interpreted as the contents of the multiline string.

GNU libmu_sieve extends the described syntax as follows.  If the keyword
@code{text:} is immediately followed by a dash (@samp{-}), then all
leading tab characters are stripped from input lines and the line
containing delimiter (@samp{.}).  This allows multiline strings within
scripts to be indented in a natural fashion.

Furthermore, if the @code{text:} (optionally followed by @samp{-}) is
immediately followed by a word, this word will be used as ending
delimiter of multiline string instead of the default dot.  For
example:        

@smallexample
@group
if header "from" "me@@example.com"
  @{
    reject text:-EOT
        I do not accept messages from
        this address.
        .
        .
        EOT
     # Notice that this the multiline string ends here.
     # The single dots above will be part of it.
    ;
  @}
@end group  
@end smallexample
@noindent

@item String Lists
@cindex string list, sieve

A @dfn{string list} is a comma-delimited list of quoted strings, enclosed
in a pair of square brackets, e.g.:

@smallexample
["me@@example.com", "me00@@landru.example.edu"]
@end smallexample

For convenience, in any context where a list of strings is appropriate,
a single string is allowed without being a member of a list: it is
equivalent to a list with a single member.  For example, the following
two statements are equivalent:

@smallexample
exists "To";
exists ["To"];
@end smallexample

@end itemize

@node Syntax
@section Syntax

Being designed for the sole purpose of filtering mail, Sieve has a very
simple syntax. 

@menu
* Commands::
* Actions Described::
* Control Flow::
* Tests and Conditions::
@end menu

@node Commands
@subsection Commands

The basic syntax element is a @dfn{command}.  It is defined as follows:

@smallexample
@var{command-name} [@var{tags}] @var{args}
@end smallexample
@noindent
where @var{command-name} is an identifier representing the name of the
command, @var{tags} is an optional list of @dfn{optional} or
@dfn{tagged arguments} and @var{args} is a list of @dfn{required} or
@dfn{positional arguments}.

Positional arguments are literals delimited with whitespace.  They
provide the command with the information necessary to its proper
functioning.  Each command has a fixed number of positional arguments.  It
is an error to supply more arguments to the command or to give it fewer
arguments than it accepts.

Optional arguments allow to modify the behaviour of the command, like
command line options in UNIX do.  They are a list of @dfn{tags}
(@pxref{Lexical Structure}) separated by whitespace.  An optional
argument may have at most one parameter.

Each command understands a set of optional arguments.  Supplying it tags
that it does not understand results in an error.

For example, consider the following command

@smallexample
header :mime :comparator "i;octet" ["to", "from"] "bug-mailutils@@gnu.org"
@end smallexample

@noindent
Here, given that @code{header} takes two positional arguments:
@code{header} is command name, the list @code{["to", "from"]} is first
positional argument and the string @code{"bug-mailutils@@gnu.org"} is second
positional argument.  There are two optional arguments: @code{:mime} and
@code{:comparator}.  The latter has a string @code{"i;octet"} as its
parameter.

@node Actions Described
@subsection Actions Described
@cindex action, sieve

An @dfn{action} is a Sieve command that performs some operation over
a message.  Actions do the main job in any Sieve
program.  Syntactically, an action is a command terminated with
semicolon, e.g.:

@smallexample
keep;

fileinto "mbox";
@end smallexample

GNU Sieve provides the full set of actions described in RFC 3028.
It also allows to extend this set using loadable
actions.  @xref{Actions}, for detailed discussion of actions.

@node Control Flow
@subsection Control Flow
@kwindex if, sieve

The only control flow statement Sieve has is @code{if} statement.  In its
simplest form it is:

@smallexample
if @code{condition} @{ @dots{} @}
@end smallexample

The effect of this statement is that the sequence of actions between the
curly braces is executed only if the @code{condition} evaluates to
@code{true}.

A more elaborate form of this statement allows to execute two
different sets of actions depending on whether the condition is
true or not:

@smallexample
if @code{condition} @{ @dots{} @} else @{ @dots{} @}
@end smallexample

The most advanced form of the ``if'' statement allows to select an
action depending on what condition from the set of conditions is met.

@smallexample
if @code{cond1} @{ @dots{} @} elsif @code{cond2} @{ @dots{} @} else @{ @dots{} @}
@end smallexample

There may be any number of ``elsif'' branches in an ``if''
statement.  However it may have at most one ``else'' branch.
Notes for C programmers:

@enumerate
@item The braces surrounding each branch of an ``if'' statement are
required.
@item The ``else if'' construct is disallowed.  Use ``elsif'' keyword
instead.
@end enumerate

Here's an example of ``if'' statement:

@smallexample
if header :contains "from" "coyote"
  @{
    discard;
  @}
elsif header :contains ["subject"] ["$$$"]
  @{
    discard;
  @}
else
  @{
    fileinto "INBOX";
  @}
@end smallexample

The following section describes in detail conditions used in ``if''
statements.

@node Tests and Conditions
@subsection Tests and Conditions
@cindex test, sieve

@dfn{Tests} are Sieve commands that return boolean value.  E.g. the
test

@smallexample
header :contains "from" "coyote"
@end smallexample

@noindent
returns true only if the header ``From'' of the current message contains
substring ``coyote''.

The tests shipped with the GNU Sieve are described in @ref{Tests}.

@cindex condition, sieve
@dfn{Condition} is a Sieve expression that evaluates to @code{true} or
@code{false}.  In its simplest form, condition is just a Sieve test.

@kwindex not, sieve
To reverse the sense of a condition use keyword @code{not}, e.g.: 

@smallexample
not header :contains "from" "coyote"
@end smallexample

@kwindex and, sieve
@kwindex or, sieve
@kwindex allof
@kwindex anyof
The results of several conditions may be joined together by logical
@code{and} and @code{or} operations.  The special form @code{allof}
takes several tests as its arguments and computes the logical @code{and}
of their results.  Similarly, the form @code{anyof} performs logical
@code{or} over the results of its arguments.  E.g.:

@smallexample
if anyof (not exists ["From", "Date"],
          header :contains "from" "fool@@example.edu")
  @{
    discard;
  @}
@end smallexample
                   
@node Preprocessor
@section Preprocessor
@cindex preprocessor, sieve
@cindex Sieve preprocessor statements

Preprocessor statements are a GNU extension to the Sieve language.
The syntax for a preprocessor statement is similar to that used in
@code{C} programming language, i.e. a pound character (@samp{#})
followed by a preprocessor directive and its arguments.  Any amount of
whitespace can be inserted between the @samp{#} and the directive.
Currently implemented directives are @code{include} and @code{searchpath}.

@menu
* #include::        Include the contents of a file.
* #searchpath::     Modify the current search path.
@end menu

@node #include
@subsection Sieve #include directive
@kwindex #include, sieve

The @code{#include} directive reads in the contents of the given file.
The contents is ``inserted'' into the text being parsed starting at the
line where the directive appears.  The directive takes two forms:

@table @code
@item #include "@var{filename}"
The @var{filename} is taken relative to the current directory.

@item #include <@var{filename}>"
The @var{filename} is searched in the list of include directories
as specified by the @option{-I} command line options.
@end table

If @var{filename} starts with a directory separator character
(@samp{/}) both forms have the same effect.

@node #searchpath
@subsection Sieve #searchpath directive
@kwindex #searchpath, sieve

The @code{#searchpath} directive adds its argument to the list of
directories searched for loadable modules.  It has the same effect
as @command{library-path} Sieve configuration statement
(@pxref{Sieve Configuration, library-path}). 

@node Require Statement
@section Require Statement
@kwindex require, sieve

@smallexample
Syntax:   require @var{string};
          require @var{string-list};
@end smallexample

The require statement informs the parser that a script makes use of a certain
extension.  Multiple capabilities can be declared using the second form
of the statement.  The actual handling of a capability name depends on
its suffix.

If the name starts with @samp{comparator-}, it is understood
as a request to use the specified comparator.  The comparator name
consists of the characters following the suffix.

If the name starts with @samp{test-}, it means a request to use
the given test.  The test name consists of the characters following
the suffix.

Otherwise, the capability is understood as a name of an action to be
used.

The @code{require} statement, if present, must be used before any other
statement that is using the required capability.  As an extension, the GNU
sieve allows the @code{require} and any other statements to be
interspersed.

By default the following actions and comparators need not be
explicitly required:

@itemize
@item stop
@item keep
@item discard
@item i;octet
@item i;ascii-casemap
@end itemize

Example:

@smallexample
require ["fileinto", "reject"];

require "fileinto";

require "comparator-i;ascii-numeric";
@end smallexample

When processing arguments for @code{require} statement, GNU libmu_sieve
uses the following algorithm:

@enumerate 1
@item Look up the name in a symbol table.  If the name begins with
@samp{comparator-} it is looked up in the comparator table.  If it
begins with @samp{test-}, the test table is used instead.  Otherwise
the name is looked up in the action table.

@item If the name is found, the search is terminated.

@item Otherwise, transform the name.  First, any @samp{comparator-} or
@samp{test-} prefix is stripped.  Then, any character other than
alphanumeric characters, @samp{.} and @samp{,} is replaced with
dash (@samp{-}).  The name thus obtained is used as a file name
of an external loadable module. 

@item Try to load the module.  The module is searched in the
following search paths (in the order given):

@enumerate 1
@item Mailutils module directory.  By default it is
@file{$prefix/lib/mailutils}.

@item Sieve library path as given with the @option{-L} options in
the command line

@item Additional search directories specified with the
@code{#searchpath} directive.

@item The value of the environment variable @env{LTDL_LIBRARY_PATH}.

@item System library search path: The system dependent library
search path (e.g. on Linux it is set by the contents of the file
@file{/etc/ld.so.conf} and the value of the environment variable
@env{LD_LIBRARY_PATH}).
@end enumerate

@vindex LTDL_LIBRARY_PATH
@vindex LD_LIBRARY_PATH
The value of @env{LTDL_LIBRARY_PATH} and @env{LD_LIBRARY_PATH} must be a
colon-separated list of absolute directories, for example,
@samp{"/usr/lib/mypkg:/lib/foo"}.

In any of these directories, @command{libmu_sieve} first attempts to find
and load the given filename.  If this fails, it tries to append the
following suffixes to the file name:

@enumerate 1
@item the libtool archive extension @samp{.la}

@item the extension used for native dynamic libraries on the host
platform, e.g., @samp{.so}, @samp{.sl}, etc.
@end enumerate

@item If the module is found, @command{libmu_sieve} executes its
initialization function (see below) and again looks up the name
in the symbol table.  If found, search terminates successfully.

@item If either the module is not found, or the symbol wasn't
found after execution of the module initialization function,
search is terminated with an error status.  @command{libmu_sieve} then
issues the following diagnostic message:

@smallexample
source for the required action NAME is not available
@end smallexample
@end enumerate

@node Comparators
@section Comparators
@cindex comparator, sieve

GNU libmu_sieve supports the following built-in comparators:

@table @code
@item i;octet
This comparator simply compares the two arguments octet by octet

@item i;ascii-casemap
It treats uppercase and lowercase characters in the @sc{ascii} subset of
@sc{utf-8} as the same.  This is the default comparator.

@item i;ascii-numeric
Treats the two arguments as @sc{ascii} representation of decimal
numbers and compares their numeric values.  This comparator must
be explicitly required prior to use.
@end table 

@node Tests
@section Tests
@cindex test, sieve

This section describes the built-in tests supported by GNU libmu_sieve.
In the discussion below the following macro-notations are used:

@table @var
@item match-type
This tag specifies the matching type to be used with the test.  It can
be one of the following:

@table @code
@kwindex :is, sieve 
@kwindex is, sieve 
@item :is
The @code{:is} match type describes an absolute match; if the contents of
the first string are absolutely the same as the contents of the
second string, they match.  Only the string ``frobnitzm'' is the string
``frobnitzm''.  The null key ``:is'' and only ``:is'' the null value.
This is the default match-type.

@kwindex :contains, sieve
@kwindex contains, sieve
@item :contains
The @code{:contains} match type describes a substring match.  If the value
argument contains the key argument as a substring, the match is true.
For instance, the string ``frobnitzm'' contains ``frob'' and ``nit'', but
not ``fbm''.  The null key ``'' is contained in all values.

@kwindex :matches, sieve
@kwindex matches, sieve
@item :matches
The @code{:matches} version specifies a wildcard match using the
characters @samp{*} and @samp{?}.  @samp{*} matches zero or more
characters, and @samp{?} matches a single character.  @samp{?} and
@samp{*} may be escaped as @samp{\\?} and @samp{\\*} in strings to match
against themselves.  The first backslash escapes the second backslash;
together, they escape the @samp{*}.

@kwindex :regex, sieve
@kwindex regex, sieve
@item :regex
The @code{:regex} version specifies a match using POSIX Extended Regular
Expressions.

@kwindex :value, sieve
@kwindex value, sieve
@item :value @var{relation}
The @code{:value} match type does a relational comparison between
strings.  Valid values for @var{relation} are:

@table @asis
@item "eq"
Equal

@item "ne"
Not Equal

@item "gt"
Greater Than

@item "ge"
Greater than or Equal

@item "lt"
Less Than

@item "le"
Less than or Equal
@end table

@kwindex :count, sieve
@kwindex count, sieve
@item :count @var{relation}
This match type first determines the number of the specified entities
(headers, addresses, etc.) in the message and does a relational
comparison of the number of entities to the values specified in the
test expression.  The test expression must be a list of one element.
@end table

@kwindex :comparator, sieve
@kwindex comparator, sieve
@item comparator
A @var{comparator} syntax item is defined as follows:

@smallexample
:comparator "@var{comparator-name}"
@end smallexample
@noindent
It instructs sieve to use the given comparator with the test.
If @var{comparator-name} is not one of @samp{i;octet},
@samp{i;ascii-casemap} it must be required prior to using it.
For example:

@smallexample
require "comparator-i;ascii-numeric";

if header :comparator "i;ascii-numeric" :is "X-Num" "10"
  @{
    ...
@end smallexample

@item address-part
This syntax item is used when testing structured Internet addresses.  It
specifies which part of an address must be used in comparisons.
Exactly one of the following tags may be used:

@table @code
@kwindex :all, sieve
@kwindex all, sieve
@item :all
Use the whole address.  This is the default.

@kwindex :localpart, sieve
@kwindex localpart, sieve
@item :localpart
Use local part of the address.

@kwindex :domain, sieve
@kwindex domain, sieve
@item :domain
Use domain part of the address.
@end table

@end table

@emph{Notice}, that @var{match-type} modifiers interact with
comparators.  Some comparators are not suitable for matching with
@code{:contains} or @code{:matches}.  If this occurs, sieve issues
an appropriate error message.  For example, the statement:

@smallexample
if header :matches :comparator "i;ascii-numeric"
@end smallexample
@noindent
would result in the following error message:

@smallexample
comparator `i;ascii-numeric' is incompatible with match type `:matches'
in call to `header'
@end smallexample

GNU Sieve supports two kinds of tests.  @dfn{Built-in tests} are
defined within the library and do not require any external files.
@dfn{External tests} are loadable modules that can be linked in at run
time using the @code{require} statement (@pxref{Require Statement}).

@menu
* Built-in Tests::
* External Tests::
@end menu

@node Built-in Tests
@subsection Built-in Tests

@deffn Test false

This test always evaluates to ``false''.
@end deffn

@deffn Test true

This test always evaluates to ``true''.
@end deffn

@deftypefn Test {} address [@var{address-part}] @
                           [@var{comparator}] @
                           [@var{match-type}] @
                           @var{header-names} @var{key-list}

@noindent
Tagged arguments:

@table @var
@item address-part
Selects the address part to compare.  Default is the whole email address
(@code{:all}).

@item comparator
Specifies the comparator to be used instead of the default @code{i;ascii-casemap}.

@item match-type
Specifies the match type to be used instead of the default @code{:is}.
@end table

@noindent
Required arguments:

@table @var
@item header-names
A list of header names.

@item key-list
A list of address values.
@end table
@noindent

The @code{address} test matches Internet addresses in structured headers
that contain addresses.  It returns @code{true} if any header contains any
key in the specified part of the address, as modified by 
@var{comparator} and @var{match-type} optional arguments.

This test returns @code{true} if any combination of the
@var{header-names} and @var{key-list} arguments match.

The @code{address} primitive never acts on the phrase part of an email
address, nor on comments within that address.  Use the @code{header} test
instead.  It also never acts on group names, although it does act on the
addresses within the group construct.

Example:

@smallexample
if address :is :all "from" "tim@@example.com"
  @{
     discard;
  @} 
@end smallexample
@end deftypefn

@deftypefn Test {} size [:over | :under] @var{limit}(number)
The @code{size} test deals with the size of a message.  The required
argument @var{limit} represents the size of the message in bytes.  It
may be suffixed with the following quantifiers:

@table @samp
@item k
@itemx K
The number is expressed in kilobytes.
@item m
@itemx M
The number is expressed in megabytes.
@item g
@itemx G
The number is expressed in gigabytes.
@end table

@kwindex :over
If the tagged argument is @samp{:over}, and the size of the message is greater
than @var{number}, the test is true; otherwise, it is false.

@kwindex :under
If the argument is @samp{:under}, and the size of the message is less than
the @var{number}, the test is true; otherwise, it is false.

Otherwise, the test is true only if the size of the message equals
exactly @var{number}.  This is a GNU extension.

The size of a message is defined to be the number of octets from the
initial header until the last character in the message body.
@end deftypefn

@deftypefn Test {} envelope [@var{address-part}] @
                            [@var{comparator}] @
                            [@var{match-type}] @
                            @var{envelope-part}(string-list) @
                            @var{key-list}(string-list)
@noindent

Tagged arguments:

@table @var
@item address-part
Selects the address part to compare.  Default is the whole email address
(@code{:all}).

@item comparator
Specifies the comparator to be used instead of the default @code{i;ascii-casemap}.

@item match-type
Specifies the match type to be used instead of the default @code{:is}.
@end table
@noindent
Required arguments:

@table @var
@item envelope-parts
A list of envelope parts to operate upon.

@item key-list
A list of address values.
@end table
@noindent

The @code{envelope} test is true if the specified part of the @sc{smtp}
envelope matches the specified key.

If the envelope-part strings is (case insensitive) @samp{from},
then matching occurs against the FROM address used in the
@command{SMTP MAIL} command.  

@emph{Notice}, that due to the limitations imposed by @sc{smtp} envelope
structure the use of any other values in @var{envelope-parts} header is
meaningless.
@end deftypefn

@deftypefn Test {} exists @var{header-names}(string-list)
@noindent

Required arguments:

@table @var
@item header-names
List of message header names.
@end table

@sp 1
@noindent
The @code{exists} test is @code{true} if the headers listed in
@var{header-names} argument exist within the message.  All of the headers
must exist or the test is false.

The following example throws out mail that doesn't have a From header
and a Date header:

@smallexample
if not exists ["From","Date"]
  @{
     discard;
  @}
@end smallexample
@end deftypefn

@deftypefn Test {} header [@var{comparator}] @
                          [@var{match-type}] @
                          [:mime] @
                          @var{header-names}(string-list) @
                          @var{key-list}(string-list)
@sp 1
@noindent
Tagged arguments:

@table @asis
@item @var{comparator}
Specifies the comparator to be used instead of the default @code{i;ascii-casemap}.

@item @var{match-type}
Specifies the match type to be used instead of the default @code{:is}.

@kwindex :mime
@item :mime
This tag instructs @code{header} to search through the mime headers in
multipart messages as well.

@end table
@sp 1
@noindent
Required arguments:

@table @var
@item header-names
A list of header names.

@item key-list
A list of header values.
@end table
@sp 1
@noindent
The @code{header} test evaluates to true if any header name matches any
key.  The type of match is specified by the optional match argument,
which defaults to ":is" if not explicitly given.

The test returns @code{true} if any combination of the @var{header-names}
and @var{key-list} arguments match.

If a header listed in @var{header-names} exists, it contains the null
key (@samp{""}).  However, if the named header is not present, it
does not contain the null key.  So if a message contained the header

@smallexample
X-Caffeine: C8H10N4O2
@end smallexample
@sp 1
@noindent
these tests on that header evaluate as follows:

@smallexample 
header :is ["X-Caffeine"] [""] @result{} false
header :contains ["X-Caffeine"] [""] @result{} true
@end smallexample
@end deftypefn

@node External Tests
@subsection External Tests

@deftypefn Test {} numaddr [:over | :under] @
                           @var{header-names}(string-list) @
                           @var{count}(number)
@noindent
@*Synopsis:
@smallexample
require "test-numaddr";
@dots{}
if numaddr @var{args}
  @{
    @dots{}
  @}
@end smallexample
@*Description: 
This test is provided as an example of loadable extension tests.  You
must use @samp{require "test-numaddr"} statement before actually using
it.

The @code{numaddr} test counts Internet addresses in structured headers
that contain addresses.  It returns true if the total number of
addresses satisfies the requested relation.

@kwindex :over
If the tagged argument is @samp{:over} and the number of addresses is
greater than @var{count}, the test is true; otherwise, it is false.

@kwindex :under
If the tagged argument is @samp{:under} and the number of addresses is
less than @var{count}, the test is true; otherwise, it is false.

If the tagged argument is not given, @samp{:over} is assumed. 
@end deftypefn

@deftypefn Test {} pipe [:envelope] [:header] [:body] @
                        [:exit @var{code}(number)] @
                        [:signal @var{code}(number)] @
                        @var{command}(string)
@*Synopsis:
@smallexample
require "test-pipe";

if pipe @var{command}
  @{
    @dots{}
  @}
@end smallexample
@*Description: 
The @code{pipe} test executes a shell command specified by its
argument and pipes the entire message (including envelope) to its
standard input.  When given, tags @code{:envelope}, @code{:header},
and @code{:body} control what parts of the message to pipe to the command.

In the absence of the @code{:exit} tag, the test returns true if
the command exits with code 0.  If @code{:exit} is given, the test returns
true if the command exits with code equal to its argument.

The @code{:signal} tag determines the result of the test in case if the program
exits on signal.  By default, the test returns false.  If @code{:signal}
is given and the number of signal which caused the program to terminate
matches its argument, the test returns true.
@end deftypefn

@deftypefn Test {} spamd [:host @var{tcp-host}(string)] @
                         [:port @var{tcp-port}(number)] @
                         [:socket @var{unix-socket}(string)] @
                         [:user @var{name}(string)] @
                         [:over | :under @var{limit}(string)]
@*Synopsis:
@smallexample
require "test-spamd";
@dots{}
if spamd @var{args}
  @{
    # @r{This is spam}
    @dots{}
  @}
@end smallexample
  
@*Description:  
This test is an interface to SpamAssassin filter.  It connects to the
@command{spamd} daemon using connection parameters specified by tagged
arguments @code{:host} and @code{:port} (if the daemon is listening on
an INET socket), or @code{:socket} (if the daemon is listening on a
UNIX socket) and returns true, if SpamAssassin qualifies the message
as spam.  Tagged argument @var{limit} alters the default behavior.  Its
value is a string representation of a floating point number.  If
the tag @code{:over} is used, then the test returns true if the spam
score returned from SpamAssassin is greater than @var{limit}.
Otherwise, if @code{:under} is used, the test returns true if the spam
score is less than @var{limit}.  The comparison takes into account
three decimal digits.

Tagged argument @code{:user} allows to select a specific user profile.
If it is not given, the user name is determined using the effective
UID.

Before returning, the @code{spamd} test adds the following headers to
the message:

@table @asis
@item X-Spamd-Status
@samp{YES} or @samp{NO}, depending on whether the message is qualified
as spam or ham.

@item X-Spamd-Score
Actual spam score value.

@item X-Spamd-Threshold
Spam score threshold, as configured in SpamAssassin settings.

@item X-Spamd-Keywords
Comma-separated list of keywords, describing the spam checks that
succeeded for this message.
@end table

Example:

@smallexample
request "test-spamd";

if spamd :host 127.0.0.1 :port 3333
  @{
     discard;
  @}
@end smallexample
  
@end deftypefn

@deftypefn Test {} list [@var{comparator}] [@var{match-type}] @
                        [ :delim @var{delimiters}(string) ] @
                @var{headers}(string-list) @var{keys}(string-list)
@*Synopsis:
@smallexample
require "test-list";
if list @var{args}
  @{
     @dots{} 
  @}
@end smallexample  
@*Description:  
The @code{list} test evaluates to true if any of @var{headers} matches any
key from @var{keys}.  Each header is regarded as containing a list of
keywords.  By default, comma is assumed as list separator.  This can be
overridden by specifying the @code{:delim} tag, whose value is a
string consisting of valid list delimiter characters.

Example:

This test can be used in conjunction with the @code{spamd} test
described above:

@smallexample
require ["fileinto", "test-spamd", "test-list"];

if spamd :host 127.0.0.1 :port 3333
  @{
     if list :matches :delim " ,"
             "X-Spamd-Keywords" [ "HTML_*", "FORGED_*" ]
       @{      
          fileinto "~/mail/spam";
       @}
     else
       @{
          discard;
       @}
  @}
@end smallexample
@end deftypefn

@deftypefn Test {} timestamp  [:before | :after] @
                   @var{header}(string) @var{date}(string)
@*Synopsis:
@smallexample
require "test-timestamp";

if timestamp @var{arg}
  @{
     @dots{}
  @}
@end smallexample
@*Description:
The @code{timestamp} test compares the value of a structured date header
field (@var{header}) with the given date (@var{date}).

If the tagged argument is @code{:after} and the date from the header is
after the specified date the result is true, otherwise, if the header
date is before the given date, the result is false. 

If the tagged argument is @code{:before} and the date from the header is
before the specified date the result is true, otherwise, if the header
date is after the given date, the result is false.

If no tagged argument is supplied, @code{:after} is assumed.

Almost any date format is understood.  @xref{Date Input Formats}, for
a detailed information on date formats.

Example:

The test below succeeds if the date in @samp{X-Expire-Timestamp}
header is more than 5 days older than the current date:

@smallexample
require "test-timestamp";

if timestamp :before "X-Expire-Timestamp" "now - 5 days"
  @{
     discard;
  @}
@end smallexample
@end deftypefn

@node Actions
@section Actions
There are two groups of GNU Sieve actions: @dfn{built-in actions},
which are defined within the library, and @dfn{external actions}, i.e.
loadable modules that can be linked in at run time using the
@code{require} statement (@pxref{Require Statement}).

@menu
* Built-in Actions::
* External Actions::
@end menu

@node Built-in Actions
@subsection Built-in Actions

The GNU libmu_sieve supports the following built-in actions:

@itemize
@item stop
@item keep
@item discard
@item fileinto
@item reject
@item redirect
@end itemize

Among them the first three actions do not need to be explicitly required
by a @code{require} statement, while the others do.

These actions are described in detail below.

@deffn Action stop

The @code{stop} action ends all processing.  If no actions have been
executed, then the @code{keep} action is taken.
@end deffn

@deffn Action keep

The effect of this action is to preserve the current message in the
mailbox.  This action is executed if no other action has been executed.
@end deffn

@deffn Action discard

@code{Discard} silently throws away the current message.  No notification
is returned to the sender, the message is deleted from the mailbox.

Example:
@smallexample
if header :contains ["from"] ["idiot@@example.edu"]
  @{
    discard;
  @}
@end smallexample
@end deffn

@anchor{fileinto}
@deffn Action fileinto [:permissions @var{mode}] @var{folder}
@noindent

Required arguments:

@table @var
@item folder
A string representing the folder name
@end table

@noindent
Tagged arguments:

@table @code
@item :permissions @var{mode}
Specifies the permissions to use, if the mailbox is created.
@end table

The @code{fileinto} action delivers the message into the specified
folder.  If the folder is local, it is created using permissions
@samp{0600}, for regular files, and @samp{0700} for directories.  This
default can be changed by using the @code{:permissions} tag.  Its
argument is a mode specification, similar to that used by
@command{chmod} shell utility.  It is a list of permissions settings
separated by commas.  Each setting begins with one of the following
letters:

@table @asis
@item g
Set permissions for the users in the file group.

@item o
Set permissions for users not in the file's group.
@end table

This letter must be followed by either @samp{+} or @samp{=} and the
list of permissions to be set.  This latter list is a string
containing any one or both of the following characters:

@table @asis
@item r
Grant permission to read.

@item w
Grant permission to write.
@end table

For example, the following instruction creates the mailbox
@file{~/shared} which will be world readable and writable
for the group:

@smallexample
  fileinto :permissions "g=rw,o=r" "~/shared"
@end smallexample

Notice that:

@enumerate 1
@item
The @code{:permissions} setting are affected by the current umask
value.

@item
Only @code{r} and @code{w} permissions can be set, since other
permissions do not seem to be useful for mailboxes.  However, for
mailboxes that have a directory structure (such as maildir and MH),
any settings in @samp{g} and @samp{o} sets imply setting the
executable bit.

@item
Owner's permissions cannot be set.  The owner always has all
permissions on the mailbox he created.

@item
The @code{:permissions} settings apply only to local mailboxes.  They
are ignored for remote mailboxes.
@end enumerate

@end deffn

@deffn Action reject @var{reason}

The optional @code{reject} action refuses delivery of a message by sending
back a message delivery notification to the sender.  It resends the
message to the sender, wrapping it in a ``reject'' form, noting that it
was rejected by the recipient.  The required argument @var{reason} is
a string specifying the reason for rejecting the message.

Example:

If the message contained
@smallexample
Date: Tue, 1 Apr 1997 09:06:31 -0800 (PST)
From: coyote@@desert.example.org
To: roadrunner@@acme.example.com
Subject: I have a present for you

I've got some great birdseed over here at my place.
Want to buy it?
@end smallexample
@noindent
@sp 1
and the user's script contained:

@smallexample
if header :contains "from" "coyote@@desert.example.org"
  @{
    reject "I am not taking mail from you, and I don't want
            your birdseed, either!";
  @}
@end smallexample
@noindent
then the original sender <coyote@@desert.example.org> would receive the
following notification:

@smallexample
To: <coyote@@desert.example.org>
X-Authentication-Warning: roadrunner set sender using -f flag
Content-Type: multipart/mixed; boundary=----- =_aaaaaaaaaa0
MIME-Version: 1.0
----- =_aaaaaaaaaa0
The original message was received at
Tue, 1 Apr 1997 09:07:15 -0800 from
coyote@@desert.example.org.
Message was refused by recipient's mail filtering program.
Reason given was as follows:

I am not taking mail from you, and I don't want your
birdseed, either!

----- =_aaaaaaaaaa0
Content-Type: message/delivery-status

Reporting-UA: sieve; GNU Mailutils 0.1.3
Arrival-Date: Tue, 1 Apr 1997 09:07:15 -0800
Final-Recipient: RFC822; roadrunner@@acme.example.com
Action: deleted
Disposition: automatic-action/MDN-sent-automatically;deleted
Last-Attempt-Date: Tue, 1 Apr 1997 09:07:15 -0800

----- =_aaaaaaaaaa0
Content-Type: message/rfc822

From: coyote@@desert.example.org
To: roadrunner@@acme.example.com
Subject: I have a present for you

I've got some great birdseed over here at my place.
Want to buy it?
----- =_aaaaaaaaaa0
@end smallexample

If the @var{reason} argument is rather long, the common approach is
to use the combination of the @code{text:} and @code{#include} keywords,
e.g.:

@smallexample
if header :mime :matches "Content-Type"
          [ "*application/msword;*", "*audio/x-midi*" ]
  @{
    reject text:
#include "nomsword.txt"
    .
    ;
  @}
@end smallexample      

@end deffn

@deffn Action redirect @var{address}
The @code{redirect} action is used to send the message to another user at
a supplied @var{address}, as a mail forwarding feature does.  This action
makes no changes to the message body or existing headers, but it may add
new headers.  It also modifies the envelope recipient.

The @code{redirect} command performs an MTA-style ``forward'' --- that
is, what you get from a @file{.forward} file using @code{sendmail} under
@sc{unix}.  The address on the SMTP envelope is replaced with the one on
the @code{redirect} command and the message is sent back
out.  @emph{Notice}, that it differs from the MUA-style forward, which
creates a new message with a different sender and message ID, wrapping
the old message in a new one.
@end deffn

@node External Actions
@subsection External Actions
  GNU Mailutils is shipped with a set of external Sieve
actions.  These actions are compiled as loadable modules and must be
required prior to use (@pxref{Require Statement}).

@deftypefn Action {}  moderator [:keep] [:address @var{address}(string)] @
                                [:source @var{sieve-file}(string)] @
                                [:program @var{sieve-text}(string)]
@*Synopsis:
@smallexample
require "moderator"
moderator @var{args};
@end smallexample
@*Description:
@cindex mailman
This action is a moderator robot for Mailman-driven mail archives.
A Mailman moderation request is a MIME message consisting of the
following three parts:

@multitable @columnfractions 0.2 0.4 0.4
@headitem N @tab Content-Type @tab Description
@item 1 @tab  text/plain      @tab Introduction for the human reader.
@item 2 @tab  message/rfc822  @tab Original submission.
@item 3 @tab  message/rfc822  @tab Mailman control message.
@end multitable

Replying to part 3 (keeping the subject intact) instructs Mailman to
discard the original submission.

Replying to part 3 while adding an `Approved:' header with the list
password in it approves the submission.

The @code{moderator} action spawns an inferior Sieve machine and
filters the original submission (part 2) through it.  If the inferior
machine marks the message as deleted, the action replies to the
control message, thereby causing the submission to be discarded.  The
@samp{From:} address of the reply can be modified using
@code{:address} tag.  After discarding the message, @code{moderator}
marks it as deleted, unless it is given @code{:keep} tag. 

If the @code{:source} tag is given, its argument specifies a Sieve
source file to be used on the message.  Otherwise, if @code{:program}
is given, its argument supplies a Sieve program to be used on this
message.  At most one of these tags may be specified.  Supplying them
both, or supplying several instances of the same tag, is an error. The
behavior of the action in this case is undefined.
   
If neither @code{:program} nor @code{:source} is given,
@code{moderator} will create a copy of the existing Sieve machine and
use it on the message.

The action checks the message structure: it will bail out if the message
does not have exactly 3 MIME parts, or if parts 2 and 3 are not of
@samp{message/rfc822} type.  It is the responsibility of the caller to
make sure the message is actually a valid Mailman moderation request
(see the example below).

@*Example:
@smallexample
if allof(header :is "Sender" "mailman-bounces@@gnu.org",
         header :is "X-List-Administrivia" "yes")
  @{
     moderator :source "~/.sieve/mailman.sv";
  @}
@end smallexample
@end deftypefn

@deftypefn Action {} pipe [:envelope] [:header] [:body] @var{command}(string)
@*Synopsis:
@smallexample
require "pipe";

pipe @var{command}
@end smallexample
@*Description:
The @code{pipe} action executes a shell command specified by its
argument and pipes the entire message (including envelope) to its
standard input.  When given, tags @code{:envelope}, @code{:header},
and @code{:body} control what parts of the message to pipe to the
command.

@*Example:
The example below uses the @command{maidag} utility
(@pxref{maidag}) to forward the message to user @samp{gray} on
the machine @samp{mail.gnu.org}.

@smallexample
require "pipe";

pipe "/usr/sbin/maidag --url smtp://gray@@mail.gnu.org"
@end smallexample
@end deftypefn

@deftypefn Action {} vacation [:days @var{ndays}(number)] @
                          [:subject @var{subject}(string)] @
                          [:aliases @var{addrlist}(string-list)] @
                          [:noreply @var{noreply-address}(string-list)] @
                          [:reply_regex @var{expr}(string)] @
                          [:reply_prefix @var{prefix}(string)] @
                          [:sender @var{email}(string)] @
                          [:database @var{path}(string)] @
                          [:return_address @var{email}(string)] @
                          [:header @var{headers}(string-list)] @
                          [:mime] @
                          [:always_reply] @
                          [:rfc2822] @
                          [:file] @
                          @var{text}(string)
@*Syntax:
@smallexample
require "vacation";
vacation @var{args};
@end smallexample
@*Description:
The @code{vacation} action returns a message with @var{text} to
the sender.  It is intended to inform the sender that the recipient is
not currently reading his mail.

If the @code{:file} tag is present, @var{text} is treated as the name
of the file to read the body of the reply message from.  When used together
with tag @code{:rfc2822}, the file should be formatted as a valid RFC
2822 message, i.e. headers followed by empty line and body.  Headers
may not contain @samp{To}, @samp{From}, and @samp{Subject}, as these
will be generated automatically.

If the @code{:subject} tag is given, its argument sets the subject of
the message.  Otherwise, the subject is formed by prefixing original
subject with @samp{Re:}, or the @var{prefix} given with the
@code{:reply_prefix} tag.  Before prefixing, any original prefixes
matching extended regular expression @var{expr} (@code{:reply_regex}
tag) are stripped from the subject line.  If @code{:reply_regex} is not
specified, the default regexp is @samp{^re: *}. 

Another headers can be added using the @code{:header} tag.  Its
argument is a list of header strings, each one having the form
@samp{"@var{name}:@var{value}"}.  Additional whitespace is allowed on
both sides of the colon.

The @code{:aliases} tag instructs @code{vacation} to handle messages
for any address in @var{addrlist} in the same manner as those received
for the user's principal email.

Before processing, @code{vacation} compares the sender address with
its @dfn{address exclusion list}.  Elements of this list are extended
case-insensitive regular expressions.  If the sender address matches
any of these expressions, the message will not be replied.  The default
exclusion list is:

@smallexample
    .*-REQUEST@@.*
    .*-RELAY@@.*
    .*-OWNER@@.*
    ^OWNER-.*
    ^postmaster@@.*
    ^UUCP@@.*
    ^MAILER@@.*
    ^MAILER-DAEMON@@.*
@end smallexample

New entries can be added to this list using @code{:noreply} tag.

The @code{:days} tag sets the @dfn{reply interval}.  A reply is sent to
each sender once in @var{ndays} days.  GNU Sieve keeps track of
sender addresses and dates in file @file{.vacation} stored in
the user's home directory.  The file name can be changed using the
@code{:database} tag.

The tag @code{:always_reply} instructs vacation to respond to the
message regardless of whether the user email is listed as a recipient
for the message.
@end deftypefn

@node Extensions
@section Extensions

The following extensions are implemented

@menu
* encoded-character::
* relational::
* variables::
* environment::
* numaddr::
* editheader::
* list::
* moderator::
* pipe::
* spamd::
* timestamp::
* vacation::
@end menu

@node encoded-character
@subsection The encoded-character extension

The @samp{encoded-character} extension complies with @cite{RFC 5228},
part 2.4.2.4.  It provides a way of incorporating multibyte sequences
in a Sieve script using only ASCII characters.  This is a built-in
extension.  It is enabled using the following statement:

@example
require "encoded-character";
@end example

When this extension is enabled, the sequences @samp{$@{hex: ...@}},
and @samp{$@{unicode: ...@}} can appear inside of quoted strings.

The sequence

@example
$@{hex: @var{XX}@}
@end example

@noindent
where @var{XX} is a sequence of one or two-digit hex numbers separated
by any amount of whitespace, is replaced with the octets with the
hexadecimal values given by each hex number.  For example,

@example
"$@{hex: 24 24@}" @result{} "$$"
@end example

Thus, the following script will discard any message containing three
contiguous dollar signs in its @samp{Subject} header:

@example
require "encoded-character";

if header :contains "Subject" "$$@{hex:24 24@}" @{
     discard;
@}
@end example

The @samp{hex:} keyword is case-insensitive.  If @var{XX} contains
invalid hex numbers, the entire sequence is left verbatim.  This is
illustrated by the following example: 

@example
"$$@{hex:40@}"         @result{} "$@@"
"$@{hex: 40 @}"        @result{} "@@"
"$@{HEX: 40@}"         @result{} "@@"
"$@{hex:40"             @result{} "$@{hex:40"
"$@{hex:400@}"         @result{} "$@{hex:400@}"
"$@{hex:4$@{hex:30@}@}"  @result{} "$@{hex:40@}"
@end example

The sequence

@example
$@{unicode: @var{HEXNUM}@}
@end example

@noindent
where @var{HEXNUM} is a list of hexadecimal numbers separated with
whitespace, will be replaced by the UTF-8 encoding of the specified
Unicode characters, which are identified by the hexadecimal value of
@var{HEXNUM}.  For example, the following string represents a single
@samp{@@} sign:

@example
"$@{UNICODE:40@}"
@end example

Similarly to @samp{hex:}, the @samp{unicode:} indicator is case
insensitive.  The following examples demonstrate the handling of
several valid and invalid encodings:

@example
"$@{unicode:40@}"      @result{} "@@"
"$@{ unicode:40@}"     @result{} "$@{ unicode:40@}"
"$@{UNICODE:40@}"      @result{} "@@"
"$@{UnICoDE:0000040@}" @result{} "@@"
"$@{Unicode:40@}"      @result{} "@@"
"$@{Unicode:Cool@}"    @result{} "$@{Unicode:Cool@}"
"$@{unicode:200000@}"  @result{} error
"$@{Unicode:DF01@}     @result{} error
@end example

@node relational
@subsection The relational extension

The @samp{relational} extension complies with @cite{RFC 3431}.  It is
a built-in extension.  When enabled, the two new match types become
available: @code{:count} and @code{:value}.  Both keywords take a
single argument defining the relational operator to use:

@multitable @columnfractions 0.2 0.8
@item @samp{"gt"} @tab greater than (@samp{>})
@item @samp{"ge"} @tab greater than or equal (@samp{>=})
@item @samp{"lt"} @tab less than (@samp{<})
@item @samp{"le"} @tab less than or equal (@samp{<=})
@item @samp{"eq"} @tab equal to (@samp{==})
@item @samp{"ne"} @tab not equal to (@samp{!=})
@end multitable

The @code{:value} keyword requires a relational comparison between
strings.  The left side of the relation is formed by the value from
the message.  The right side of the relation is the value from the
test expression.  If there are multiple values on either side or both
sides, the test is considered true if any pair is true.  For example,

@example
require ["relational", "fileinto"];

if header :value "gt" :comparator "i;ascii-numeric"
                ["x-spam-level] ["5"]
@{
  fileinto "spam";
@}  
@end example

The @code{:count} keyword counts the specified entities in the message
and compares their number with the value given in the test
expression.  The latter must be a list of one element.  This match
type can only be used with numeric comparators.  For example, the
following script will discard any message with 10 or more recipient
addresses in the @samp{To} and @samp{Cc} headers:

@example
require "relational";

if address :count "ge" :comparator "i;ascii-numeric"
                      ["to", "cc"] ["10"]
@{
    discard;
@}
@end example

@node variables
@subsection The variables extension

The @samp{variables} extension is defined in @cite{RFC 5229}.  It is
a built-in extension.  It introduces support for variables in Sieve
scripts.

There are two kind of variables: user-defined and match variables.

A @dfn{user-defined} variable is initialized using the @code{set}
action:

@deftypefn Action {} set [@var{modifiers}] @var{name}(string) @var{value}(string)
Stores the specified @var{value} in the variable identified by
@var{name}.  Optional @var{modifiers} are applied on @var{value} before it
is stored in the variable.

The following modifiers are available:

@table @code
@item :lower
Convert value to lower case letters.
@item :upper
Convert value to upper case letters.

@item :lowerfirst
Convert the first character in value to lower case.

@item :upperfirst
Convert the first character in value to upper case.

@item :quotewildcard
Quote wildcard characters (@samp{*}, @samp{?}, @samp{\}) by prefixing
each occurrence with a backslash (@samp{\}).  This can be used to
ensure that the variable will only match a literal occurrence if used
as a parameter to @code{:matches}.

@item :length
The value is the decimal number of characters in the expansion,
converted to a string.
@end table

When several modifiers are present, they are applied in the following
order of precedence (largest value first):

@multitable @columnfractions 0.2 0.8
@headitem precedence @tab modifiers
@item 40 @tab @code{:lower} or @code{:upper}
@item 30 @tab @code{:lowerfirst} or @code{:upperfirst}
@item 20 @tab @code{:quotewildcard}
@item 10 @tab @code{:length}
@end multitable

Modifiers having the same precedence (i.e. listed on the same row in
the above table) cannot be used together.
@end deftypefn

Variables are referenced within text strings using the construct
@samp{$@{@var{name}@}}, where @var{name} is the name of the variable
as it appeared in the first parameter to the @code{set} statement.
For example:

@example
require "variables";

set "sender" "root@*":

if envelope :matches "$@{sender@}"
@{
   ...
@}
@end example

@dfn{Match variables} refer to parts of the most recently evaluated
successful match of type @code{:matches} or @code{:regex}.  They have
names consisting entirely of decimal digits.  The variable
@samp{$@{0@}} refers to the entire matched expression.  The variable
@samp{$@{1@}} refers to the substring matching the first occurrence of
the wildcard (@samp{?} and @samp{*}), @samp{$@{2@}} refers to the
second occurrence and so on.  The wildcards match as little as possible
(non-greedy matching).  For example:

@example
require ["variables", "fileinto"];

if header :matches "List-ID" "*<*@*" @{
   fileinto "INBOX.lists.$@{2@}";
   stop;
@}
@end example

If @code{:regex} match is used, the match variables starting from
@samp{$@{1@}} refer to the substrings of the argument value matching
subsequent parenthesized groups of the regular expression.  

@deftypefn Test {} string [@var{comparator}] @
                          [@var{match-type}] @
                          @var{source}(string-list) @var{keys}(string-list)
The @code{string} test compares two strings according to the selected
comparator and match type.   The test evaluates to @samp{true} if any
two strings from @var{source} and @var{keys} match.

The @samp{:count} match used in @samp{string} counts each empty string
as 0, and each non-empty one as 1.  The count of a string list is the
sum of the counts of the member strings.
@end deftypefn

@node environment
@subsection environment

The @samp{environment} extension complies with @cite{RFC 5183}.  It is
a built-in extension.  It introduces the following test:

@deftypefn Test {} environment [@var{comparator}] @
                               [@var{match-type}] @
                               @var{name}(string) @var{keys}(string-list)
The @code{environment} test evaluates to @samp{true} if the value of
the environment items @var{name} matches any string from @var{keys}.
@end deftypefn

The following environment items are defined:

@table @asis
@item domain
The primary DNS domain of the machine where the Sieve script is
executing.

@item host
The fully-qualified domain name of the host where the Sieve script is
executing. 

@item location
Type of service that is evaluating the script.   Depending on the
utility that is evaluating the script it is:

@multitable @columnfractions 0.6 0.4
@headitem Utility @tab Location
@item sieve @tab @samp{"MUA"}, or set with the @option{--environment} option.
@item maidag @tab @samp{"MDA"}
@item inc @tab @samp{"MUA"}
@end multitable

@item name
The string @samp{GNU Mailutils}

@item phase
The point relative to final delivery where the Sieve script is being
evaluated.  Depending on the utility that is evaluating the script it is:

@multitable @columnfractions 0.6 0.4
@headitem Utility @tab Location
@item sieve @tab @samp{post} unless set with the @option{--environment} option.
@item maidag @tab @samp{"during"}
@item inc @tab @samp{"post"}
@end multitable

@item version
Mailutils version string (e.g. @samp{@value{VERSION}}).
@end table

@node numaddr
@subsection The numaddr extension

This is an example loadable extension.  @ref{External Tests, numaddr}.

@node editheader
@subsection The editheader extension

The @code{editheader} extension complies with @cite{RFC 5293}.  It
provides the following actions:

@deftypefn Action {} addheader [:last] @var{field-name}(string) @var{value}(string
Adds a header field to the existing message header.  By default the
header is inserted at the beginning of the header list.  If the tag
@code{:last} is specified, it is appended at the end.
@end deftypefn

@deftypefn Action {} deleteheader" [:index @var{fieldno}(number) :last] @
                                   [@var{comparator}] @
                                   [@var{match-type}] @
                                   @var{field-name}(string) @
                                   [@var{value-patterns}(string-list)]
                                   
Deletes occurrences of the header field matching the criteria.

The @var{value-patterns}, if specified, determines which occurrences
of the header fielde to delete.  If not supplied, @var{comparator} and
@var{match-type} are silently ignored.

If @samp{:index @var{fieldno}} is specified, only the numbered
occurrence of the named header field will be matched (header numbering
begins at 1),  If @code{:last} is specified, the count is backwards; 1
denotes the last named header field, 2 the second to last, and so on.
The counting happens before the @var{value-patterns} match, if any.
Thus, e.g. the action

@example
deleteheader :index 1 :contains "Delivered-To" "bob@@example.com";
@end example

@noindent
would delete the first @samp{Delivered-To} header field if it contains
the string @samp{bob@@example.com}.
@end deftypefn

@node list
@subsection The list extension

@ref{External Tests, list}.

@node moderator
@subsection The moderator extension

A loadable extension implementing a moderator robot for Mailman-driven
mail archives.  @ref{External Actions, moderator}.

@node pipe
@subsection The pipe extension

A loadable extension for external command execution.  It provides the
@code{pipe} action (@pxref{External Actions, pipe}) and test
(@pxref{External Tests, pipe}).  

@node spamd
@subsection The spamd extension

Implements a test which interfaces to SpamAssassin filter.  This is a
loadable extension.  @pxref{External Tests, spamd}.

@node timestamp
@subsection The timestamp extension

The loadable extension @code{timestamp} implements a test for 
comparing the value of a structured date header field with the given
date.

Note: this extension will probably phase away in favor of the
@code{date} Sieve extension (@cite{RFC 5260}).

@node vacation
@subsection The vacation extension

The loadable extension @code{vacation} provides the action intended to
inform the sender that the recipient is not currently reading his mail.

@xref{External Actions,vacation}.

@node GNU Extensions
@section GNU Extensions

This section summarizes the GNU extensions to the sieve language

@enumerate 1
@item Multiline strings syntax

GNU libmu_sieve understands the following multiline string syntax:

@smallexample
@group
text:[-][@var{delimiter}]
....
@var{delimiter}
@end group
@end smallexample

The meaning of optional flags is the same as in shell ``here document''
construct: the dash strips all leading tab characters from the string body,
thus allowing it to be indented in a natural fashion; @var{delimiter}
introduces the new end-of-text delimiter instead of the default
dot.  If @var{delimiter} starts with a backslash, no preprocessing will
be performed within a string.

@item Handling of the @code{require} statement.

@itemize
@item According to the RFC an error must occur if a @code{require} appears
after a command other than @code{require}.  The GNU sieve library allows
interspersing the @code{require} and other statements.  The only
requirement is that @code{require} must occur before a statement that is
using the required capability (@pxref{Require Statement}).

@item Prefixing the required capability with ``test'' requires the use
of an extension test.
@end itemize

@item @code{header} test

The @code{header} takes an optional argument @code{:mime}, meaning to
scan the headers from each part of a multipart message.

@item @code{size} test

The @code{size} test allows to omit the optional argument
(:over|:under).  In this case exact equality is assumed.

@item @code{envelope} test

The only value that can be meaningfully used as the first required
argument of an @code{envelope} test is @samp{from}.  This limitation
may disappear from the subsequent releases.

@item @code{fileinto} action

The @code{fileinto} action allows to specify permissions on the mailbox,
in case it will be created (@pxref{fileinto}).

@item Match type optional argument.

Along with the usual @code{:is}, @code{:matches} and @code{:contains}
matching type, GNU sieve library understands @code{:regex} type.  This
matching type toggles POSIX Extended Regular Expression matching.
@end enumerate