@c This is part of the GNU Mailutils manual.
@c Copyright (C) 1999--2022 Free Software Foundation, Inc.
@c See file mailutils.texi for copying conditions.
@comment *******************************************************************

GNU Mailutils provides a broad set of utilities for handling
electronic mail.  These utilities address the needs of both system
administrators and users.

All utilities are built around a single core subsystem and share many
common aspects.  All of them are able to work with almost any existing
mailbox formats.  They use a common configuration file syntax, and
their configuration files are located in a single subdirectory.

In this chapter we will discuss each utility, and give some advices on
how to use them in various real life situations.

First of all we will describe command line and configuration file
syntax.

@menu
* command line::      Command Line Syntax.  
* configuration::     Common Configuration File.
* debugging::

* frm and from::      List Headers from a Mailbox.
* mail::              Send and Receive Mail.
* messages::          Count the Number of Messages in a Mailbox.
* movemail::          Moves Mail from the User Maildrop to the Local File.
* readmsg::           Extract Messages from a Folder.
* decodemail::        Decode multipart messages.

* sieve::             Mail Filtering Utility.
* guimb::             Mailbox Scanning and Processing Language.

* mda::               Local Mail Delivery Agent.
* lmtpd::             LMTP Daemon.
* putmail::           Incorporate a Message to a Mailbox.

* mimeview::          Universal File Viewer.

* pop3d::             POP3 Daemon.
* imap4d::            IMAP4 Daemon.
* comsatd::           Comsat Daemon.

* mh::                The MH Message Handling System.

* mailutils::         The Mailutils Multi-Purpose Tool.
* dotlock::           The External Locker Utility. 
@end menu

@node command line
@section Command Line

@menu
* Option Basics::       Basic Notions About Command Line Options.
* Common Options::      Options That are Common for All Utilities.
@end menu

@node Option Basics
@subsection Basic Notions About Command Line Options

  Many command line options have two forms, called short and long
forms.  Both forms are absolutely identical in function; they are
interchangeable. 

  The @dfn{short} form is a traditional form for UNIX utilities.
In this form, the option consists of a single dash, followed by a
single letter, e.g.  @option{-c}.

  Short options which require arguments take their arguments
immediately following the option letter, optionally separated by white
space.  For example, you might write @option{-f name}, or @option{-fname}.
Here, @option{-f} is the option, and @option{name} is its argument.

  Short options which allow optional arguments take their arguments
immediately following the option letter, @emph{without any intervening
white space characters}.  This is important, so that the command line
parser might discern that the text following option is its argument,
not the next command line parameter.  For example, if option @option{-d}
took an optional argument, then @option{-dname} would mean the option
with its argument (@option{name} in this case), and @option{-d name} would
mean the @option{-d} option without any argument, followed by command
line argument @option{name}.

  Short options' letters may be clumped together, but you are not
required to do this.  When short options are clumped as a set, use one
(single) dash for them all, e.g.  @option{-cvl} is equivalent to @option{-c
-v -l}.  However, only options that do not take arguments may be
clustered this way.  If an option takes an argument, it can only be
the last option in such a cluster, otherwise it would be impossible to
specify the argument for it.  Anyway, it is much more readable to
specify such options separated.

  The @dfn{long} option names are probably easier to memorize than
their short counterparts.  They consist of two dashes, followed by a
multi-letter option name, which is usually selected to be a mnemonics
for the operation it requests.  For example, @option{--verbose} is a
long option that increases the verbosity of a utility.  In addition,
long option names can abbreviated, provided that such an abbreviation
is unique among the options understood by a given utility.  For
example, if a utility takes options @option{--foreground} and
@option{--forward}, then the shortest possible abbreviations for these
options are @option{--fore} and @option{--forw}, correspondingly.  If
you try to use @option{--for}, the utility will abort and inform you
that the abbreviation you use is ambiguous, so it is not clear which
of the options you intended to use.

  Long options which require arguments take those arguments following
the option name.  There are two ways of specifying a mandatory
argument.  It can be separated from the option name either by an equal
sign, or by any amount of white space characters.  For example, if the
@option{--file} option requires an argument, and you wish to supply
@file{name} as its argument, then you can do so using any of the
following notations: @option{--file=name} or @option{--file name}.

  In contrast, optional arguments must always be introduced using an
equal sign.

@node Common Options
@subsection Options That are Common for All Utilities.

  All GNU Mailutils programs understand a common subset of options.

@table @option
@xopindex{help, described}
@item --help
@itemx -?
  Display a short summary of the command line options understood by
this utilities, along with a terse description of each.

  The output of this option consists of three major parts.  First, a
usage synopsis is displayed.  For example:

@example
@group
Usage: sieve [OPTION...] SCRIPT
GNU sieve -- a mail filtering tool
@end group
@end example

  The first line tells that the @command{sieve} utility takes any
number of options (brackets indicate optional part) and a single
mandatory argument (@samp{SCRIPT}).  The second lines summarizes the
purpose of the utility.

  Following this header is an option summary.  It consists of two
columns:

@verbatim
  -c, --compile-only         Compile script and exit
  -d, --debug[=FLAGS]        Debug flags
  -e, --email=ADDRESS        Override user email address
@end verbatim


The leftmost column contains a comma-separated list of option
names.  Short options are listed first.  The options are ordered
alphabetically.  Arguments, if any, are specified after the last
option name in the list, so that, e.g. the option @samp{-e} in the
example above requires an argument: @samp{-e ADDRESS}.  Optional
arguments are enclosed in square brackets, as in @option{--debug}
option in the example above.

The rightmost column contains a short description of the option
purpose. 

  The last part of @option{--help} output contains some additional
notices and lists the email address for reporting bugs.

@xopindex{usage, described}
@item --usage
Display a short summary of options.  In the contrast to the
@option{--help} option, only option names and arguments
are printed, without any textual description.  For example:

@example
@group
Usage: sieve [-cv?V] [--compile-only] [--debug[=FLAGS]]
             [--email=ADDRESS] SCRIPT
@end group
@end example
@end table

  The exact formatting of the output produced by these two options is
configurable.  @xref{Usage Vars}, for a detailed descriptions of it.

@table @option
@xopindex{version, described}
@item --version 
@itemx -V
Print program version and exit.

@xopindex{show-config-options, described}
@item --show-config-options
Show configuration options used when compiling the package.  You can
use this option to verify if support for a particular mailbox format
or other functionality is compiled in the binary.  The output of this
option is intended to be both machine-readable and understandable by
humans.
@end table

  The following command line options affect parsing of configuration
files.  Here we provide a short summary, the next section will
describe them in detail.

@table @option
@xopindex{config-file, introduced}
@item --config-file=@var{file}
Load this configuration file, instead of the default.

@xopindex{config-help, introduced}
@item --config-help
Show configuration file summary.

@xopindex{config-lint, introduced}
@item --config-lint
Check configuration file syntax and exit

@xopindex{config-verbose, introduced}
@item --config-verbose
Verbosely log parsing of the configuration files.

@xopindex{no-site-config, introduced}
@item --no-site-config
Do not load site-wide configuration file.

@xopindex{no-user-config, introduced}
@item --no-user-config
Do not load user configuration file.

@xopindex{no-config, introduced}
@item --no-config
Don't load site-wide and user configuration files.

@xopindex{set, introduced}
@item --set=@var{path}=@var{value}
Set configuration variable.  @xref{the --set option}.
@end table

@node configuration
@section Mailutils Configuration File
@cindex Mailutils configuration file
@cindex mailutils.conf

  Configuration files are the principal means of configuring any GNU
Mailutils component.  When started, each utility tries to load its
configuration from the following locations, in that order:

@enumerate 1
@item Main site-wide configuration file.

It is named @file{@var{sysconfdir}/mailutils.conf}, where
@var{sysconfdir} stands for the system configuration directory set
when compiling the package. You can obtain the value of @var{sysconfdir} by running

@example
$ mailutils info sysconfdir
@end example

@noindent
or

@example
$ @var{prog} --show-config-options | grep SYSCONFDIR
@end example

@noindent
where @var{prog} stands for any GNU Mailutils utility.

@xopindex{no-site-config, described}
The site-wide configuration file is not read if any of
@option{--no-site-config} or @option{--no-config} command line options
was given.

Older versions of GNU Mailutils read configuration from file
@file{mailutils.rc}.  To facilitate transition, mailutils will look
for that file as well.  If both the default site-wide configuration
file and legacy configuration file are present you will get the
following warning:

@example
legacy configuration file /etc/mailutils.rc ignored
@end example

Otherwise, if @file{mailutils.conf} does not exist and
@file{mailutils.rc} is present, it will be used instead and the
following warning will be issued:

@example
 using legacy configuration file /etc/mailutils.rc:
 please rename it to /etc/mailutils.conf
@end example

@item Per-user configuration file.

Client utilities, such as @command{frm} or @command{sieve}, look in
the user home directory for a file named @samp{.@var{prog}}, where
@var{prog} is the name of the utility.  If present, this file will be
loaded after loading the site-wide configuration file.  For example,
the per-user configuration file for @command{sieve} utility is named
@file{.sieve}.

@xopindex{no-user-config, described}
Loading of per-user configuration file is disabled by
@option{--no-user-config} and @option{--no-config} options.
@end enumerate

Server programs, such as @command{imap4d} don't use per-user
configuration files.

The @option{--no-config} option provides a shortcut for disabling
loading of the default configuration files.  For servers, its effect
is the same as of @option{--no-site-config}.  For client utilities, it
is equivalent to @option{--no-site-config --no-user-config} used
together.

@xopindex{config-file, described}
The @option{--config-file} command line option instructs the program
to read configuration from the file supplied as its argument.  In that
case, default configuration files are not used at all.

@xopindex{config-verbose, described}
Neither site-wide nor user configuration files are required to
exist.  If any or both of them are absent, GNU Mailutils won't
complain -- the utility will silently fall back to its default
settings.

To make configuration processing more verbose, use the
@option{--config-verbose} command line option.  Here is an example of
what you might get using this option:

@example
imap4d: parsing file `/etc/mailutils.conf'
imap4d: finished parsing file `/etc/mailutils.conf'
@end example

Specifying this option more than once adds more verbosity to this
output.  If this option is given two times, GNU Mailutils will print
each configuration file statement it parsed, along with the exact
location where it occurred (the exact meaning of each statement will
be described later in this chapter):

@example
imap4d: parsing file `/etc/mailutils.conf'
@hashchar{} 1 "/etc/mailutils.conf"
mailbox @{
@hashchar{} 2 "/etc/mailutils.conf"
  mailbox-pattern maildir:/var/spool/mail;type=index;param=2;user=$@{user@};
@hashchar{} 3 "/etc/mailutils.conf"
  mailbox-type maildir;
@};
@hashchar{} 6 "/etc/mailutils.conf"
include /etc/mailutils.d;
imap4d: parsing file `/etc/mailutils.d/imap4d'
...
@end example

@xopindex{config-lint, described}
  To test configuration file without actually running the utility,
use the @option{--config-lint} command line option.  With this option,
any Mailutils utility exits after finishing parsing of the
configuration files.  Any errors occurred during parsing are displayed
on the standard error output.  This option can be combined with
@option{--config-verbose} to obtain more detailed output.

@xopindex{config-help, described}
  The @option{--config-help} command line option produces on the
standard output the summary of all configuration statements understood
by the utility, with detailed comments and in the form suitable for
configuration file.  For example, the simplest way to write a
configuration file for, say, @command{imap4d} is to run

@example
$ imap4d --config-help > imap4d.conf
@end example

@noindent
and to edit the @file{imap4d.conf} file with your editor of choice.

The order in which configuration files are loaded defines the
precedence of their settings.  Thus, for client utilities, settings
from the per-user configuration file override those from the site-wide
configuration.

@xopindex{set, described}
  It is also possible to set or override arbitrary configuration
variables in the command line.  It can be done via the @option{--set}
option.  Its argument is a @dfn{pathname} of the variable to be set,
followed by an equals sign and a value.  For example, to define the
variable @samp{syslog} in section @samp{logging} to @samp{no}, do the
following: 

@example
$ imap4d --set .logging.syslog=no
@end example

Configuration pathnames are discussed in detail in @ref{Paths}.  For a
detailed description of this option, @ref{the --set option}.

The @option{--set} options are processed after loading all
configuration files.

@menu
* conf-syntax::         Configuration File Syntax
* Variables::           Variable Expansion
* include::             Include Statement
* program statement::
* logging statement::
* debug statement::
* mailbox statement::
* mime statement::
* locking statement::
* mailer statement::
* acl statement::
* tcp-wrappers statement::
* Server Settings::
* auth statement::
* pam statement::
* virtdomain statement::
* radius statement::
* sql statement::
* ldap statement::
* tls statement::
* tls-file-checks statement::
* gsasl statement::
@end menu

@node conf-syntax
@subsection Configuration File Syntax
  The configuration file consists of statements and comments.

  There are three classes of lexical tokens: keywords, values, and
separators.  Blanks, tabs, newlines and comments, collectively called
@dfn{white space} are ignored except as they serve to separate
tokens.  Some white space is required to separate otherwise adjacent 
keywords and values.

@menu
* Comments::
* Statements::
* Paths::
@end menu

@node Comments
@subsubsection Comments
@cindex Comments in a configuration file
@cindex single-line comments
  @dfn{Comments} may appear anywhere where white space may appear in the
configuration file.  There are two kinds of comments:
single-line and multi-line comments.  @dfn{Single-line} comments start
with @samp{#} or @samp{//} and continue to the end of the line:

@example
# This is a comment
// This too is a comment
@end example

@cindex multi-line comments
  @dfn{Multi-line} or @dfn{C-style} comments start with the two
characters @samp{/*} (slash, star) and continue until the first
occurrence of @samp{*/} (star, slash).

  Multi-line comments cannot be nested.  However, single-line comments
may well appear within multi-line ones.

@node Statements
@subsubsection Statements
@cindex statements, configuration file
@cindex configuration file statements
@cindex statement, simple
@cindex simple statements
  A @dfn{simple statement} consists of a keyword and value
separated by any amount of whitespace.  Simple statement is terminated
with a semicolon (@samp{;}).

  The following is a simple statement:

@example
standalone yes;
pidfile /var/run/pop3d.pid;
@end example

  A @dfn{keyword} begins with a letter and may contain letters,
decimal digits, underscores (@samp{_}) and dashes (@samp{-}).
Examples of keywords are: @samp{expression}, @samp{output-file}.

  A @dfn{value} can be one of the following:

@table @asis
@item number
  A number is a sequence of decimal digits.

@anchor{boolean value}  
@item boolean
@cindex boolean value
  A boolean value is one of the following: @samp{yes}, @samp{true},
@samp{t} or @samp{1}, meaning @dfn{true}, and @samp{no},
@samp{false}, @samp{nil}, @samp{0} meaning @dfn{false}.
  
@item unquoted string
@cindex string, unquoted
  An unquoted string may contain letters, digits, and any of the
following characters: @samp{_}, @samp{-}, @samp{.}, @samp{/},
@samp{@@}, @samp{*}, @samp{:}.

@item quoted string
@cindex quoted string
@cindex string, quoted
@cindex escape sequence
  A quoted string is any sequence of characters enclosed in
double-quotes (@samp{"}).  A backslash appearing within a quoted
string introduces an @dfn{escape sequence}, which is replaced
with a single character according to the following rules:

@float Table, backslash-interpretation
@caption{Backslash escapes}
@multitable @columnfractions 0.30 .5
@item Sequence @tab Replaced with
@item \a @tab Audible bell character (@acronym{ASCII} 7)
@item \b @tab Backspace character (@acronym{ASCII} 8)
@item \f @tab Form-feed character (@acronym{ASCII} 12)
@item \n @tab Newline character (@acronym{ASCII} 10)
@item \r @tab Carriage return character (@acronym{ASCII} 13)
@item \t @tab Horizontal tabulation character (@acronym{ASCII} 9)
@item \v @tab Vertical tabulation character (@acronym{ASCII} 11)
@item \\ @tab A single backslash (@samp{\})
@item \" @tab A double-quote.
@end multitable
@end float

  In addition, the sequence @samp{\@var{newline}} is removed from
the string.  This allows to split long strings over several
physical lines, e.g.:

@example
@group
"a long string may be\
 split over several lines"
@end group
@end example

  If the character following a backslash is not one of those specified
above, the backslash is ignored and a warning is issued.

  Two or more adjacent quoted strings are concatenated, which gives
another way to split long strings over several lines to improve
readability.  The following fragment produces the same result as the
example above:

@example
@group
"a long string may be"
" split over several lines"
@end group
@end example

@anchor{here-document}
@item Here-document
@cindex here-document
  A @dfn{here-document} is a special construct that allows to introduce
strings of text containing embedded newlines.  

  The @code{<<@var{word}} construct instructs the parser to read all
the following lines up to the line containing only @var{word}, with
possible trailing blanks.  Any lines thus read are concatenated
together into a single string.  For example:

@example
@group
<<EOT
A multiline
string
EOT
@end group
@end example

  The body of a here-document is interpreted the same way as a
double-quoted string, unless @var{word} is preceded by a backslash
(e.g.  @samp{<<\EOT}) or enclosed in double-quotes, in which case
the text is read as is, without interpretation of escape sequences.

  If @var{word} is prefixed with @code{-} (a dash), then all leading
tab characters are stripped from input lines and the line containing
@var{word}.  Furthermore, if @code{-} is followed by a single space,
all leading whitespace is stripped from them.  This allows to indent
here-documents in a natural fashion.  For example:

@example
@group
<<- TEXT
    The leading whitespace will be
    ignored when reading these lines.
TEXT
@end group
@end example

  It is important that the terminating delimiter be the only token on
its line.  The only exception to this rule is allowed if a
here-document appears as the last element of a statement.  In this
case a semicolon can be placed on the same line with its terminating 
delimiter, as in: 

@example
help-text <<-EOT
        A sample help text.
EOT;
@end example

@anchor{list values}
@item list
@cindex list
  A @dfn{list} is a comma-separated list of values.  Lists are
enclosed in parentheses.  The following example shows a statement
whose value is a list of strings:

@example
alias (test,null);
@end example

  In any case where a list is appropriate, a single value is allowed
without being a member of a list: it is equivalent to a list with a
single member.  This means that, e.g.

@example
alias test;
@end example

@noindent
is equivalent to

@example
alias (test);
@end example
@end table

@cindex statement, block
@cindex block statement
  A @dfn{block statement} introduces a logical group of 
statements.  It consists of a keyword, followed by an optional value,
and a sequence of statements enclosed in curly braces, as shown in
the example below:

@example
@group
server srv1 @{
  host 10.0.0.1;
  community "foo";
@}
@end group
@end example

  The closing curly brace may be followed by a semicolon, although
this is not required.

@node Paths
@subsubsection Statement Path

@command{Mailutils} configuration files have a distinct hierarchical
structure.  Each statement in such files can therefore be identified
by its name and the names of block statements containing it.  Such
names form the @dfn{pathname}, similar to that used by UNIX file system.

For example, consider the following file:

@example
foo @{
  bar @{
    baz 45;   # @r{A.}
  @}
  baz 98;     # @r{B.}
@}
@end example

The full pathname of the statement marked with @samp{A} can be written
as:

@example
.foo.bar.baz
@end example

Similarly, the statement marked with @samp{B} has the following
pathname:

@example
.foo.baz
@end example

The default path component separator is dot.  A pathname beginning with
a component separator is called @dfn{absolute pathname}.  Absolute
pathnames uniquely identify corresponding statements.  If the leading
dot is omitted, the resulting pathname is called
@dfn{relative}.  Relative pathnames identify statements in relation to 
the current point of reference in the configuration file.

Any other punctuation character can be used as a component separator,
provided that it appears at the beginning of the pathname.  In other
words, only absolute pathnames allow for a change in component separators.

A block statement that has a tag is referred to by the statement's
name, followed by an equals sign, followed by the tag value.  For
example, the statement @samp{A} in the file below:

@example
program x @{
  bar @{
    baz 45;   # @r{A.}
  @}
@}
@end example

is identified by the following pathname:

@example
.program=x.bar.baz
@end example

The tag can optionally be enclosed in a pair of double quotes.  Such a
quoting becomes mandatory for tags that contain white space or path
component separator, e.g.:

@example
.program="a.out".bar.baz
@end example

@anchor{the --set option}
The @option{--set} command line option allows you to set configuration
variables from the command line.  Its argument consists of the
statement path and value, separated by a single equals sign (no
whitespace is permitted at either side of it).  For example, the
following option:

@example
--set .logging.facility=mail
@end example

@noindent
has the same effect as the following statement in the configuration
file:

@example
logging @{
    facility mail;
@}
@end example

Values set using this option override those set in the configuration
files.  This provides a convenient way for temporarily changing
configuration without altering configuration files.

Notice, that when using @option{--set}, the @samp{=} sign has two
purposes: first it separates statement path from the value, thus
forming an assignment, and secondly it can be used within the path
itself to introduce a tag.  To illustrate this, let's assume you have
the following statement in your configuration file:

@example
@group
program pop3d @{
    logging @{
       facility mail;
    @}
    server 0.0.0.0 @{
       transcript no;
    @}
@}
@end group
@end example

Now assume you wish to temporarily change logging facility to
@samp{local1}.  The following option will do this:

@example
--set .program=pop3d.logging.facility=local1
@end example

When splitting the argument to @option{--set}, the option parser
always looks for the rightmost equals sign.  Everything to the right
of it is the value, and everything to the left of it - the path.

If the tag contains dots (as the @code{server} statement in the
example above), you should either escape them with slashes or change
the pathname separator to some other character, e.g.:

@example
--set .program=pop3d.server='0\.0\.0\.0'.transcript=yes
@end example

@noindent
or

@example
--set /program=pop3d/server="0.0.0.0"/transcript=yes
@end example

@node Variables
@subsection Configuration Variables
@cindex variable expansion
@cindex macro variable
  Certain configuration statements allow for the use of variable
references in their values.  A variable reference has the form
@samp{$@var{variable}} or @samp{$@{@var{variable}@}}, where
@var{variable} is the variable name.  It is expanded to the actual
value of @var{variable} when Mailutils consults the configuration
statement in question.  

The two forms are entirely equivalent.  The form with curly braces is
normally used if the variable name is immediately followed by an
alphanumeric symbol, which will otherwise be considered part of it.
This form also allows for specifying the action to take if the
variable is undefined or expands to an empty value. 

During variable expansion, the forms below cause Mailutils to test
for a variable that is unset or null.  Omitting the colon results
in a test only for a variable that is unset.

@table @asis
@item $@{@var{variable}:-@var{word}@}
@dfn{Use Default Values}.  If @var{variable} is unset or null, the expansion
of @var{word} is  substituted.   Otherwise, the value of @var{variable} is
substituted.

@item $@{@var{variable}:=@var{word}@}
@dfn{Assign Default Values}.  If @var{variable} is unset or null, the
expansion  of @var{word} is assigned to variable.  The value of 
@var{variable} is then substituted.
                            
@item $@{@var{variable}:?@var{word}@}
@dfn{Display Error if Null or Unset}.  If @var{variable} is null or unset,
the expansion of @var{word} (or a message to that effect if @var{word} is
not present) is output to the current logging channel.  Otherwise, the
value of @var{variable} is substituted.

@item $@{@var{variable}:+@var{word}@}
@dfn{Use Alternate Value}.  If @var{variable} is null or unset, nothing is
substituted, otherwise the expansion of @var{word} is substituted.
@end table

When a value is subject to variable expansion, it is also subject to
@dfn{command expansion}.  Commands are invoked in string values using
the following format:

@example
$(@var{cmd} @var{arg})
@end example

@noindent
where @var{cmd} is the command name, and @var{args} is a list of
arguments separated by whitespace.  Arguments can in turn contain
variable and command references.

The following commands are defined:

@deffn {Command} localpart @var{string}
Treats @var{string} as an email address and returns the part preceding
the @samp{@@} sign.  If there is no @samp{@@} sign, returns @var{string}.
@end deffn

@deffn {Command} domainpart @var{string}
Treats @var{string} as an email address and returns the part following
the @samp{@@} sign.  If there is no @samp{@@} sign, returns empty string.
@end deffn

@deffn {Command} shell @var{cmd} @var{args}
Runs the shell command @var{cmd} with the given arguments.  Returns
the standard output from the command.  The command is invoked
using @command{/bin/sh -c} and can contain any valid shell constructs.
@end deffn

The subsections below define variable names that are valid for use in
each configuration statement.

@node include
@subsection The @code{include} Statement
@anchor{Include} @c for backward-compatibility
@cindex include statement, configuration file
@kwindex include
  A special statement is provided that causes inclusion of the named
file.  It has the following syntax: 

@example
include @var{file};
@end example

When reading the configuration file, this statement is effectively
replaced with the content of @var{file}.  It is an error if @var{file}
does not exist.

In site-wide configuration file, @var{file} can be a directory name.
In this case, Mailutils will search this directory for a file with the
same name as the utility being executed.  If found, this file will be
loaded.

It is a common to end the site-wide configuration file with
an include statement, e.g.:

@example
include /etc/mailutils.d;
@end example

This allows each particular utility to have its own configuration
file.  Thus, @command{imap4d} will read
@file{/etc/mailutils.d/imap4d}, etc.

@node program statement
@subsection The @command{program} statement
@kwindex program
Another way to configure program-specific settings is by using the
@command{program} statement.  The syntax is as follows:

@example
program @var{progname} @{
   ...
@}
@end example

The @command{program} statement is allowed only in the site-wide
configuration file.  When encountered, its tag (@var{progname}) is
compared with the name of the program being run.  If two strings are
the same, the statements between curly braces are stored in a
temporary memory, otherwise the statement is ignored.  When entire
configuration file is loaded, the statements accumulated in the
temporary storage are processed.

Notice the difference between this statement and a per-program
configuration file loaded via an @code{include} statement.  No matter
where in the file the @command{program} statement is, its content will
be processed after the content of the enclosing file.  In the
contrast, the per-program configuration file loaded via @code{include}
is processed right where it is encountered.

@node logging statement
@subsection The @code{logging} Statement
@anchor{Logging Statement}
@kwindex logging
@subheading Syntax
@example
logging @{
  # @r{Send diagnostics to syslog.}
  syslog @var{boolean};
  
  # @r{Print message severity levels.}
  print-severity @var{boolean};
  
  # @r{Output only messages with a severity equal to or}
  # @r{greater than this one.}
  severity @var{string};
  
  # @r{Set syslog facility.}
  facility @var{name};

  # Log session ID
  session-id @var{boolean};
    
  # @r{Tag syslog messages with this string.}
  tag @var{text};
@}
@end example

@subheading Description
  The @code{logging} block statement configures where the diagnostic
output goes and how verbose it is.

@deffn {Configuration} syslog bool
If @samp{syslog} is set to @samp{yes}, the diagnostics will go to
syslog.  Otherwise, it goes to the standard error.
@end deffn

The default syslog facility is determined at compile time, it can be inspected
using the following command (@pxref{mailutils info}):

@example
$ mailutils info log_facility
@end example

@anchor{syslog facility}
@deffn {Configuration} facility name
Use syslog facility @var{name}.  Valid argument values are: @samp{user},
@samp{daemon}, @samp{auth}, @samp{authpriv}, @samp{mail}, @samp{cron},
@samp{local0} through @samp{local7} (all names case-insensitive), or
a facility number.
@end deffn

@deffn {Configuration} tag text
Tag syslog messages with @var{text}.  By default, program name is used
as syslog tag.
@end deffn

@deffn {Configuration} print-severity bool
Print Mailutils severity name before each message.
@end deffn

@deffn {Configuration} severity name
Output only messages with a severity equal to or greater than this
one.  Valid arguments are: @samp{debug}, @samp{info}, @samp{notice},
@samp{warning}, @samp{error}, @samp{crit}, @samp{alert}, @samp{emerg},
@end deffn

@deffn {Configuration} session-id bool
Print session ID with each diagnostic message.  This is useful for
programs that handle multiple user sessions simultaneously, such as
@command{pop3d} and @command{imap4d}.
@end deffn

@node debug statement
@subsection The @code{debug} Statement
@anchor{Debug Statement}
@kwindex debug
@subheading Syntax
@example
debug @{
  # @r{Set Mailutils debugging level.}
  level @var{spec};
  
  # @r{Prefix debug messages with Mailutils source locations.}
  line-info @var{bool};
@}
@end example

@subheading Description
@kwindex level
The @samp{debug} statement controls the amount of additional debugging
information output by Mailutils programs.  The @samp{level} statement
enables additional debugging information.  Its argument (@var{spec})
is a Mailutils debugging specification as described in
@ref{debugging}.

@kwindex line-info
The @samp{line-info} statement, when set to @samp{true} causes
debugging messages to be prefixed with locations in Mailutils source
files where they appear.  Normally, only Mailutils developers need
this option. 

@node mailbox statement
@subsection The @code{mailbox} Statement
@anchor{Mailbox Statement}
@kwindex mailbox
@subheading Syntax
@example
mailbox @{
  # @r{Use specified @var{url} as a mailspool.}
  mail-spool @var{url};
  
  # @r{Create mailbox @var{url} using @var{pattern}.}
  mailbox-pattern @var{pattern};
  
  # @r{Default mailbox type.}
  mailbox-type @var{type};
  
  # @r{Default user mail folder.}
  folder @var{dir};
@}
@end example

@subheading Description
The @code{mailbox} statement configures the location, name and type of
user mailboxes.

The mailbox location can be specified using @code{mail-spool} or
@code{mail-pattern} statements.

@deffn {Configuration} mail-spool @var{path}
The @code{mail-spool} statement specifies directory that holds user
mailboxes.  Once this statement is given, the @command{libmailutils}
library will assume that the mailbox of user @var{login} is kept in
file @file{@var{path}/@var{login}}.

Historically, @var{path} can contain mailbox type prefix, e.g.:
@samp{maildir:///var/spool/mail}, but such usage is discouraged in
favor of @code{mailbox-pattern} statement.
@end deffn

@deffn {Configuration} mailbox-pattern @var{url}
The @code{mailbox-pattern} statement is a preferred way of configuring
mailbox locations.  It supersedes @code{mail-spool} statement.

The @var{url} must be a valid mailbox URL (@pxref{Mailbox}), which 
may contain references to the @samp{user} variable
(@pxref{Variables}).  This variable will be expanded to the actual
user name.

@anchor{local URL parameters}
@cindex directory indexing
Optional URL parameters can be used to configure @dfn{indexed directory
structure}.  Such structure is a special way of storing mailboxes,
which allows for faster access in case of very large number of users. 

By default, all user mailboxes are stored in a single directory and
are named after user login names.  To find the mailbox for a given
user, the system scans the directory for the corresponding
file.  This usually implies linear search, so the time needed to
locate a mailbox is directly proportional to the ordinal number of
the mailbox in the directory.

GNU Mailutils supports three types of indexed directories:
@samp{direct}, @samp{reverse}, and @samp{hashed}.

@cindex direct indexing
@cindex indexing, direct
In direct indexed directory structure, @var{path} contains 26 subdirectories
named with lower-case letters of Latin alphabet.  The location of the
user mailbox is determined using the following algorithm:

@enumerate 1
@item Take the first letter of the user name.
@item Map it to a lower-case letter using @dfn{index mapping}
table.  The result gives the name of a sub-directory where the mailbox
is located.
@item Descend into this directory.
@end enumerate

For example, using this algorithm, the mailbox of the user
@samp{smith} is stored in file @file{@var{path}/s/smith}.

If each of single-letter subdirectories contains the
indexed directory structure, we have second level of indexing.  In
this case the file name of @samp{smith}'s mailbox is
@file{@var{path}/s/m/smith}.

@cindex reverse indexing
@cindex indexing, reverse
The @dfn{reverse} indexed structure uses the same principles, but the
indexing letters are taken from the @emph{end} of the user name,
instead of from the beginning.  For example, in the 2nd level reverse
indexed structure, the @samp{smith}'s mailbox is located in
@file{@var{path}/h/t/smith}.

@cindex hashed indexing
@cindex indexing, hashed
Finally, the @dfn{hashed} structure consists of 256 subdirectories
under @var{path}, named by 2-letter hex codes from @samp{00} to
@samp{FF}.  Mailboxes are stored in these subdirectories.  The name
of the subdirectory is computed by hashing first @var{level} letters
of the user name.  The hashing algorithm is:

@enumerate 1
@item Take next letter from the user name
@item Add its ASCII value to the hash sum.
@item Continue (1-2) until @var{level} letters are processed, or all
letters from the file name are used, whichever occurs first.
@item Convert the computed sum modulo 256 to a hex code.
@end enumerate

Indexed directory structures are configured using the following
arguments:

@table @asis
@kwindex type
@item type=@var{value}
Specifies the type of indexing.  Valid values are @samp{index}, for direct
indexed structure, @samp{rev-index} for reverse indexing, and
@samp{hash} for hashed structure.

@kwindex param
@item param=@var{number}
Specifies indexing level.

@kwindex user
@item user=@var{string}
Specifies indexing key.  The only meaningful value, as of Mailutils
version @value{VERSION} is @samp{user=$@{user@}}.
@end table

Let's assume the traditional mail layout, in which incoming
mails are stored in a UNIX mailbox named after the recipient user name
and located in @file{/var/mail} directory.
The @code{mailbox-pattern} for this case is:

@example
  mailbox-pattern "/var/mail/$@{user@}";
@end example

It is entirely equivalent to specifying @samp{mail-spool "/var/mail"}.

Now, if the layout is the same, but mailboxes are kept in
@samp{maildir} format, then the corresponding statement is:

@example
  mailbox-pattern "maildir:///var/mail/$@{user@}";
@end example

Finally, if the mailboxes are stored in a directly-indexed directory with
two levels of indexing, the URL is:

@example
  mailbox-pattern "maildir:///var/mail;type=index;param=2;user=$@{user@}";
@end example
@end deffn

If neither @code{mailbox-pattern} nor @code{mail-spool} are given, the
mailbox names are determined using the following algorithm:

@enumerate 1
@item If environment variable @env{FOLDER} is set, use its value.
@item Otherwise, if environment variable @env{MAIL} is set, use its
value.
@item If neither of these is set, construct the mailbox name by 
concatenating the built-in mail spool directory name, a directory
separator, and the user name.

The built-in mail spool directory name is determined at compile
time, using the @samp{_PATH_MAILDIR} define from the include file
@file{paths.h}.  If this value is not defined, @file{/var/mail} or
@file{/usr/spool/mail} is used.
@end enumerate

@deffn {Configuration} mailbox-type @var{type}
@anchor{mailbox-type}
@vrindex MU_DEFAULT_SCHEME
Specifies the type of mailboxes.  By default, @samp{mbox} (UNIX mailbox)
is assumed.  This can be changed while configuring the package by
setting @code{MU_DEFAULT_SCHEME} configuration variable.  The default
value can be verified by running @command{mailutils info scheme}.
@end deffn

@deffn {Configuration} folder @var{dir}
@cindex plus expansion
Sets user mail folder directory.  Its value is used when expanding
@samp{plus-notation}, i.e. such mailbox names as @file{+inbox}.  The
@samp{+} sign is replaced by @var{dir}, followed by a directory
separator (@samp{/}).

The @var{dir} argument can contain mailbox type prefix, e.g
@samp{mh://Mail}.

The default folder name is @samp{Mail/}.
@end deffn

@node mime statement
@subsection The @command{mime} Statement
@kwindex mime
@subheading Syntax
@example
@group
mime @{
  # Define additional textual mime types.
  text-type PATTERN;
  # or
  text-type ( PATTERN-LIST );
@}
@end group
@end example

@subheading Description
The @code{mime} compound statement is used by utilities that process
MIME messages, in particular @command{mail}, @command{readmsg}, and
@command{decodemail}.  As of mailutils version @value{VERSION} it
contains only one statement:

@deffn {Configuration} text-type @var{pattern}
@deffnx {Configuration} text-type ( @var{pattern-list} )
Defines additional patterns for recognition of textual message parts.
The @var{pattern} is a shell globbing pattern that will be compared
against the @samp{Content-Type} header of a MIME message part in order
to determine whether it can be treated as a text part.  In second
form, @var{pattern-list} is a comma-separated list of such patterns.

In both forms, the new patterns are appended to the built-in textual
pattern list, which contains:

@itemize @bullet
@item text/*
@item application/*shell
@item application/shellscript
@item */x-csrc
@item */x-csource
@item */x-diff
@item */x-patch
@item */x-perl
@item */x-php
@item */x-python
@item */x-sh
@end itemize

@end deffn

@node locking statement
@subsection The @command{locking} Statement
@anchor{Locking Statement}
@kwindex locking
@subheading Syntax
@example
locking @{
  # @r{Default locker flags.}
  type @code{default} | @code{dotlock} | @code{external} | @code{kernel} | @code{null};
  
  # @r{Set the maximum number of times to retry acquiring the lock.}
  retry-count @var{number};
  
  # @r{Set the delay between two successive locking attempts.}
  retry-sleep @var{arg};
  
  # @r{Expire locks older than this amount of time.}
  expire-timeout @var{number};

  # @r{Check if PID of the lock owner is active, steal the lock if it not.} 
  pid-check @var{bool};

  # @r{Use @var{prog} as external locker program.}
  external-locker @var{prog};
@}
@end example

@subheading Description
This compound statement configures various parameters used when locking
UNIX mailboxes in order to prevent simultaneous writes.

It is important to note, that locking applies only to monolithic
mailboxes, i.e. mailboxes of @samp{mbox} and @samp{dotmail} types
(@pxref{mbox}).  Other mailbox types don't require locking.

@deffn {Configuration} type @var{string}
Set locking type.  Allowed arguments are:

@table @code
@item default
Default locking type.  As of @command{mailutils} version
@value{VERSION}, this is equivalent to @code{dotlock}.

@item dotlock
@anchor{dotlock locking type}
A @samp{dotlock}-style locking.  To lock a mailbox named @var{X}
a @dfn{lock file} named @file{@var{X}.lock} is created.  If 
@code{pid-check yes} is set, this file will contain the PID of the
locking process, so that another process wishing to acquire the lock
could verify if the lock is still in use.

@item external
@anchor{external locking type}
Run external program to perform locking/unlocking operations.  The
name of the program is given by the @code{external-locker} statement
(see below).  If it is not given, the built-in default @samp{dotlock}
is used.

The locker program is invoked as follows:

@example
# To lock @var{mbox}:
@var{locker} -f@var{expire_timeout} -r@var{retry_count} @var{mbox}
# To unlock it:
@var{locker} -u -f@var{expire_timeout} -r@var{retry_count} @var{mbox}
@end example

@noindent
Here, @var{expire_timeout} is the value supplied with the
@code{expire-timeout} configuration statement, and @var{retry_count}
is the value supplied with the @code{retry-count} statement (see below).

To properly interact with @command{mailutils}, the external locker
program must use the following exit codes:

@multitable @columnfractions 0.3 0.6
@headitem Exit code @tab Meaning
@item 0 @tab Success.
@item 1 @tab Failed due to an error.
@item 2 @tab Unlock requested (@option{-u}), but file is not locked.
@item 3 @tab Lock requested, but file is already locked.
@item 4 @tab Insufficient permissions.
@end multitable

@xref{dotlock}, for the description of the default external locker,
shipped with mailutils.

@item kernel
Use kernel locking mechanism (@code{fcntl}(2)).

@item null
No locking at all.  The statements below are silently ignored.
@end table
@end deffn

@deffn {Configuration} retry-count @var{number}
Number of locking attempts.  The default is 10.
@end deffn

@deffn {Configuration} retry-sleep @var{seconds}
@deffnx {Configuration} retry-timeout @var{seconds}
Time interval, in seconds, between two successive locking
attempts.  The default is 1 second.  The @code{retry-timeout}
statement is deprecated because of its misleading name.
@end deffn

@deffn {Configuration} expire-timeout @var{seconds}
Sets the expiration timeout.  The existing lock file will be removed,
if it was created more than this number of seconds ago.  The default
is 600.
@end deffn

@deffn {Configuration} pid-check @var{bool}
This statement can be used if locking type is set to @code{dotlock}.
If set to @code{true}, it instructs the locking algorithm to check
if the PID of the lock owner is still running by the time when it
tries to acquire the lock.  This works as follows.  When the lock file
is created, the PID of the creating process is written to it.  If
another process tries to acquire the lock and sees that the lock file
already exists, it reads the PID from the file and checks if a process
with that PID still exists in the process table.  If it does not, the
process considers the lock file to be stale, removes it and locks the
mailbox.
@end deffn

@deffn {Configuration} external-locker @var{string}
Sets the name of the external locker program to use, instead of the
default @samp{dotlock}.

This statement is in effect only when used together with @code{type external}.
@end deffn

@node mailer statement
@subsection The @code{mailer} Statement
@anchor{Mailer Statement}
@kwindex mailer
@subheading Syntax
@example
mailer @{
  url @var{url};
@}
@end example

@subheading Description
A @dfn{mailer} is a special logical entity GNU Mailutils uses for
sending messages.  Its internal representation is discussed in
@FIXME-ref{Mailer}.  The @code{mailer} statement configures it.

The mailer statement contains a single sub-statement:

@deffn {Configuration} url @var{str}
Set the mailer @acronym{URL}.
@end deffn

@anchor{mailer URL}
GNU Mailutils supports three types of mailer @acronym{URL}s, described
in the table below:

@table @asis
@item smtp://[@var{user}[:@var{pass}][;auth=@var{mech},...]@@]@var{host}[:@var{port}][;@var{params}]
@itemx smtps://[@var{user}[:@var{pass}][;auth=@var{mech},...]@@]@var{host}[:@var{port}][;@var{params}] 
Send messages using SMTP protocol.  @xref{SMTP Mailboxes}, for a
detailed description of the URL and its parts.

@item sendmail[://@var{progname}]
Use sendmail-compatible program
@var{progname}.  @dfn{Sendmail-compatible} means that the program must
support following command line options:

@table @option
@item -oi
Do not treat @samp{.} as message terminator.

@item -f @var{addr}
Use @var{addr} as the sender address.

@item -t
Get recipient addresses from the message.
@end table

@xref{Program Mailboxes,,sendmail}, for details.

@item prog://@var{progname}?@var{query}
A @dfn{prog} mailer.  This is a generalization of @samp{sendmail}
mailer that allows to use arbitrary external programs as mailers.

It is described in detain in @ref{Program Mailboxes,,prog}.
@end table

@node acl statement
@subsection The @code{acl} Statement
@anchor{ACL Statement}
@kwindex acl
@subheading Syntax
@example
acl @{
  # @r{Allow connections from this IP address.}
  allow [from] @var{ip};
  
  # @r{Deny connections from this IP address.}
  deny [from] @var{ip};
  
  # @r{Log connections from this IP address.}
  log [from] @var{ip} [@var{string}];
  
  /* @r{Execute supplied program if a connection from this
     IP address is requested.} */
  exec [from] @var{ip} @var{program};
  
  /* Use @var{program} to decide whether to allow connection
     from @var{ip}. */
  ifexec [from] @var{ip} @var{program};
@}
@end example

@subheading Description
The ACL statement defines an @dfn{Access Control List}, a special
structure that controls who can access the given Mailutils resource.

The @code{acl} block contains a list of access controls.  Each control
can be regarded as a function that returns a tree-state value:
@samp{True}, @samp{False} and @samp{Don't know}.  When a
remote party connects to the server, each of controls is tried in
turn.  If a control returns @samp{False}, access is denied.  If it
returns @samp{True}, access is allowed.  If it returns @samp{Don't
know}, then the next control is tried.  It is unclear whether to allow
access if the last control in list returned @samp{Don't know}.  GNU
Mailutils @value{VERSION} issues a warning message and allows access.
This default may change in future versions.  Users are advised to
write their ACLs so that the last control returns a definite answer
(either @code{True} or @code{False}).

In the discussion below, wherever @var{cidr} appears as an argument, it
can be replaced by any of: 

@itemize @bullet
@item An IPv4 address in dotted-quad notation.
@item An IPv6 address in numeric notation
@item A CIDR in the form @samp{@var{ip}/@var{mask}}, where @var{ip} is
an IP address (either IPv4 or IPv6), and @var{mask} is the network mask.
@item A symbolic host name.
@kwindex any
@item A word @samp{any}, which matches any IP address.
@end itemize

The following controls are understood:

@deffn {Configuration} allow [from] @var{cidr}
Allow connections from IP addresses matching this @var{cidr} block.
@end deffn

@deffn {Configuration} deny [from] @var{cidr}
Deny connections from IP addresses matching this @var{cidr} block.
@end deffn

@deffn {Configuration} ifexec [from] @var{cidr} @var{program}
When a connection from the @var{cidr} block is requested, execute
the program @var{program}.  If its exit code is @samp{0}, then allow
connection.  Otherwise, deny it.

The @var{program} argument undergoes variable expansion and word
splitting.  The following variables are defined:

@table @code
@item aclno
Ordinal number of the control in the ACL.  Numbers begin from
@samp{1}.

@item family
Connection family.  Mailutils version @value{VERSION} supports the following
families: @samp{AF_INET}, @samp{AF_INET6} and @samp{AF_UNIX}.

@item address
Remote IP address (for @samp{AF_INET} and @samp{AF_INET6}) or socket name (for
@samp{AF_UNIX}).  Notice that most Unixes return empty string instead
of the @samp{AF_UNIX} socket name, so do not rely on it.

@item port
Remote port number (for @samp{AF_INET} and @samp{AF_INET6}).
@end table
@end deffn

@deffn {Configuration} exec [from] @var{cidr} @var{program}
If a connection from the @var{cidr} block is requested, execute the given
@var{program}.  Do not wait for it to terminate, and ignore its exit
code.  The @var{program} is subject for variable expansion as in
@samp{ifexec}.
@end deffn

The following two controls are provided for logging purposes and as a
means of extensions.  They always return a @samp{Don't know} answer,
and therefore should not be used at the end of an ACL:

@deffn {Configuration} log [from] @var{cidr} [@var{string}]
Log connections from addresses in this @var{cidr}.  The
@code{MU_DIAG_INFO} channel is used.  If the logging goes to syslog,
it is translated to the @code{LOG_INFO} priority.

If @var{string} is not given, the format of the log entry depends on
the connection family, as described in the table below:

@table @asis
@item @{AF_INET @var{ip}:@var{port}@}
For inet IPv4 connections.  The variables @var{ip} and @var{port} are
replaced by the remote IP address and port number, correspondingly.

@item @{AF_UNIX@}
For connections over UNIX sockets.  The socket name, if available, may
be printed before the closing curly brace.
@end table

If @var{string} is supplied, it undergoes variable expansions as
described for the @samp{ifexec}.

For example, the following ACL makes a Mailutils server log every
incoming connection:

@example
  acl @{
     log from any "Connect from $@{address@}";
     ...
  @}
@end example

This was the default behavior for the versions of Mailutils up to
@samp{1.2}, so if you got used to its logs you might wish to add the
above in your configuration files.
@end deffn

@deffn {Configuration} exec [from] @var{cidr} @var{program}
If a connection from the @var{cidr} block is requested, execute
the given @var{program}.  Do not wait for it to terminate, and ignore
its exit code.
@end deffn

@node tcp-wrappers statement
@subsection The @code{tcp-wrappers} Statement
@anchor{Tcp-wrappers Statement}
@kwindex tcp-wrappers
@subheading Syntax
@example
tcp-wrappers @{
  # @r{Enable TCP wrapper access control.}
  enable @var{bool};
  
  # @r{Set daemon name for TCP wrapper lookups.}
  daemon @var{name};
  
  # @r{Use @var{file} for positive client address access control.}
  allow-table @var{file};
  
  # @r{Use file for negative client address access control.}
  deny-table @var{file};
@}
@end example

@subheading Description
The @code{tcp-wrappers} statements provides an alternative way to
control accesses to the resources served by GNU Mailutils.  This
statement is enabled if Mailutils is compiled with TCP wrappers
library @command{libwrap}.

Access control using TCP wrappers is based on two files, called
@dfn{tables}, containing access rules.  There are two tables: the
@dfn{allow table}, usually stored in file @file{/etc/hosts.allow}, and
the @dfn{deny table}, kept in file @file{/etc/hosts.deny}.  The rules
in each table begin with an identifier called @dfn{daemon name}.  A
utility that wishes to verify a connection, selects the entries having
its daemon name from the allow table.  A connection is allowed if it
matches any of these entries.  Otherwise, the utility retrieves all
entries with its daemon name from the deny table.  If any of these
matches the connection, then it is refused.  Otherwise, if neither
table contains matching entries, the connection is allowed.

The description of a TCP wrapper table format lies outside the scope of
this document.  Please, see @ref{ACCESS CONTROL FILES,,ACCESS CONTROL FILES,
hosts_access(5), hosts_access(5) man page}, for details.

@deffn {Configuration} enable @var{bool}
Enable access control using TCP wrappers.  It is on by default.
@end deffn

@deffn {Configuration} daemon @var{name}
Set daemon name for TCP wrapper lookups.  By default, the name of the
utility is used.  E.g.  @command{imap4d} uses @samp{imap4d} as the
daemon name.
@end deffn

@deffn {Configuration} allow-table @var{file}
Use @var{file} as allow table.  By default, @file{/etc/hosts.allow} is
used. 
@end deffn
  
@deffn {Configuration} deny-table @var{file}
Use @var{file} as negative table.  By default, @file{/etc/hosts.deny}
is used.
@end deffn

@node Server Settings
@subsection Server Settings
@cindex server settings, configuration
@cindex configuring servers
  GNU Mailutils offers several server applications: @command{pop3d},
@command{imap4d}, @command{comsatd}, to name a few.  Being quite
different in their purpose, they are very similar in some aspects of
their architecture.  First of all, they all support two operating
modes: @dfn{daemon}, where a program disconnects from the controlling
terminal and works in background, and @dfn{inetd}, where it
remains in foreground and communicates with the remote party via
standard input and output streams.  Secondly, when operating as
daemons, they listen to a preconfigured set of IP addresses and
ports, reacting to requests that arrive.

  To configure these aspects of functionality, GNU Mailutils provides
@dfn{Server Configuration Settings}, which is describes in this
subsection. 

@menu
* General Server Configuration::
* Server Statement::
@end menu

@node General Server Configuration
@subsubsection General Server Configuration
@cindex server configuration, general
@* Syntax:
@example
# @r{Set daemon mode.}
mode @samp{inetd|daemon};

# @r{Run in foreground.}
foreground @var{bool};

# @r{Maximum number of children processes to run simultaneously.}
max-children @var{number};

# @r{Store PID of the master process in @var{file}.}
pidfile @var{file};

# @r{Default port number.}
port @var{portspec};

# @r{Set idle timeout.}
timeout @var{time};
@end example

@* Description:
These statements configure general server-related issues.

@deffn {Configuration} mode @var{string};
Set operation mode of the server.  Two operation modes are supported:

@anchor{server mode}
@table @asis
@cindex daemon, server mode
@item daemon
Run as a standalone daemon, disconnecting from the controlling
terminal and continuing to run in the background.  In this case, it is
the server that controls what IP addresses and ports to listen on, who
is allowed to connect and from where, how many clients are allowed to
connect simultaneously, etc.  Most remaining configuration statements
are valid only in the daemon mode.

This is the preferred mode of operation for GNU Mailutils servers.

@cindex inetd, server mode
@item inetd
Operate as a subprocess of UNIX internet super-server program,
@command{inetd}.  @xref{Internet super-server,,,inetd(8), inetd(8) man
page}, for a detailed description of the operation of @command{inetd}
and its configuration.  In this case it is @command{inetd} that
controls all major connectivity aspects.  The Mailutils server program
communicates with it via standard input and output streams.

For historical reasons, this mode is the default, if no @code{mode}
statement is specified.  This will change in the future.
@end table
@end deffn

@deffn {Configuration} foreground @var{bool};
@*[daemon mode only]
@*Do not disconnect from the controlling terminal and remain in the
foreground. 
@end deffn

@deffn {Configuration} max-children @var{number};
@*[daemon mode only]
@*Set maximum number of child processes allowed to run simultaneously.
This equals the number of clients that can use the server
simultaneously.

The default is 20 clients.
@end deffn

@deffn {Configuration} pidfile @var{file};
After startup, store the PID of the main server process in
@var{file}.  When the process terminates, the file is removed.  As of
version @value{VERSION}, GNU Mailutils servers make no further use of
this file.  It is intended for use by automated startup scripts and
controlling programs (e.g. @pxref{Top, GNU pies,, pies, GNU Pies Manual}).
@end deffn

@deffn {Configuration} port @var{portspec};
@*[daemon mode only]
@*Set default port to listen to.  The @var{portspec} argument is either
a port number in decimal, or a symbolic service name, as listed in
@file{/etc/services} (@pxref{Internet network services list,,,
services(5), services(5) man page}).
@end deffn

@deffn {Configuration} timeout @var{time};
Sets maximum idle time out in seconds.  If a client does not send any
requests during @var{time} seconds, the child process terminates.
@end deffn

@node Server Statement
@subsubsection The @code{server} Statement
@cindex server statement
@kwindex server
@* Syntax:
@example
server @var{ipaddr}[:@var{port}] @{
  # @r{Run this server as a single process.}
  single-process @var{bool};
  
  # @r{Log the session transcript.}
  transcript @var{bool};

  # @r{Set idle timeout.}
  timeout @var{time};

  # Size of the queue of pending connections
  backlog <number: callback>;

  # @r{Kind of TLS encryption to use for this server.}
  tls-mode @samp{no}|@samp{ondemand}|@samp{required}|@samp{connection};

  tls @{
    # @r{Specify SSL certificate file.}
    ssl-certificate-file @var{string};
    # @r{Specify SSL certificate key file.}
    ssl-key-file @var{file};
    # @r{Specify trusted CAs file.}
    ssl-ca-file @var{file};
    # @r{Set the priorities to use on the ciphers, methods, etc.}
    ssl-priorities @var{string};
    # @r{Set timeout for I/O operations during TLS handshake (seconds).}
    handshake-timeout @var{n};
  @}
  
  # @r{Set server specific ACLs.}
  acl @{ /* @xref{ACL Statement}. */ @};
@}
@end example

@* Description:

The @code{server} block statement configures a single TCP or UDP
server.  It takes effect only in daemon mode (@pxref{server mode}).
The argument to this statement specifies the IP address, and,
optionally, the port, to listen on for requests.  The @var{ipaddr}
part is either an IPv4 address in dotted-quad form, or a IPv6 address
enclosed in square brackets, or a symbolic host name which can be
resolved to such an address.  Specifying @samp{0.0.0.0} as the
@var{ipaddr} means listen on all available network interfaces.  The
@var{port} argument is either a port number in decimal, or a symbolic
service name, as listed in @file{/etc/services} (@pxref{Internet
network services list,,,services(5), services(5) man page}).  If
@var{port} is omitted, Mailutils uses the port set by @code{port}
statement (@pxref{General Server Configuration, port}), or, in its
absence, the default port number, which depends on a server being used
(e.g. 110, for @command{pop3d}, 143, for @command{imap4d}, etc.).  

Any number of @code{server} statements may be specified in a single
configuration file, allowing to set up the same service on several IP
addresses and/or port numbers, and with different configurations.

Statements within the @code{server} block statement configure this
particular server.

@deffn {Configuration} single-process @var{bool};
If set to true, this server will operate in single-process mode.  This
mode is intended for debugging only, do not use it on production
servers.
@end deffn

@deffn {Configuration} transcript @var{bool};
Enable transcript of the client-server interaction.  This may generate
excessive amounts of logging, which in turn may slow down the operation
considerably.

Session transcripts are useful in fine-tuning your configurations and
in debugging.  They should be turned off on most production servers.
@end deffn

@deffn {Configuration} timeout @var{time};
Set idle timeout for this server.  This overrides the global timeout
settings (@pxref{General Server Configuration, timeout}).
@end deffn

@deffn {Configuration} backlog @var{number};
Configures the size of the queue of pending connections
@end deffn

@deffn {Configuration} tls-mode @var{mode};
Configure the use of TLS encryption.  The @var{mode} argument is one
of the following:

@table @asis
@item no
TLS is not used.  The corresponding command (@command{STLS}, for POP3,
@command{STARTTLS}, for @command{IMAP4}) won't be available even if
the TLS configuration is otherwise complete.

@item ondemand
TLS is initiated when the user issues the appropriate command.
This is the default when TLS is configured.

@item required
Same as above, but the use of TLS is mandatory.  The authentication
state is entered only after TLS negotiation has succeeded.

@item connection
TLS is always forced when the connection is established.  For
@command{pop3d} this means using POP3S protocol (or IMAP4S, for
@command{imap4d}).
@end table
@end deffn

@deffn {Configuration} tls @{ ... @}
The @code{tls} statement configures SSL certificate and key files, as
well as other SSL settings for use in this server.  It is used when
@code{tls-mode} is set to any of the following values:
@code{ondemand}, @code{required}, @code{connection}.

If @code{tls-mode} is set to any of the values above and @code{tls}
section is absent, settings from the global @code{tls} section will
be used.  In this case, it is an error if the global @code{tls}
section is not defined.

@xref{tls statement}, for a discussion of its syntax.
@end deffn

@deffn {Configuration} acl
This statement defines a per-server Access Control List.  Its syntax
is as described in @ref{ACL Statement}.  Per-server ACLs complement,
but not override, global ACLs, i.e. if both global ACL and per-server
ACL are used, the connection is allowed only if both of them allow it,
and is denied if any one of them denies it.
@end deffn

@node auth statement
@subsection The @code{auth} Statement
@anchor{Auth Statement}
@cindex authorization
@cindex authentication
@kwindex auth
@subheading Syntax
@example
auth @{
  # @r{Set a list of modules for authentication.}
  authentication @var{module-list};
  
  # @r{Set a list of modules for authorization.}
  authorization @var{module-list};
@}
@end example

@subheading Description
Some mail utilities provide access to their services only after
verifying that the user is actually the person he is claiming
to be.  Such programs are, for example, @command{pop3d} and
@command{imap4d}.  The process of the verification is broken
down into two stages: @dfn{authorization} and @dfn{authentication}.
In @dfn{authorization} stage the program retrieves the information
about a particular user.  In @dfn{authentication} stage, this
information is compared against the user-supplied credentials.  Only if
both stages succeed is the user allowed to use the service.

A set of @dfn{modules} is involved in performing each stage.  For
example, the authorization stage can retrieve the user description
from various sources: system database, SQL database, virtual domain
table, etc.  Each module is responsible for retrieving the description
from a particular source of information.  The modules are arranged in
a @dfn{module list}.  The modules from the list are invoked in turn,
until one of them succeeds or the list is exhausted.  In the latter case 
the authorization fails.  Otherwise, the data returned by the succeeded
module are used in authentication.

Similarly, authentication may be performed in several ways.  The
authentication modules are also grouped in a list.  Each module
is tried in turn until either a module succeeds, in which case the
authentication succeeds, or the end of the list is reached.

For example, the authorization list

@example
  (system, sql, virtdomains)
@end example

@noindent
means that first the system user database (@file{/etc/password}) is
searched for a description of a user in question.  If the search fails,
the @acronym{SQL} database is searched.  Finally, if it also fails, the
search is performed in the virtual domain database.

@emph{Note}, that some authentication and/or authorization modules may
be disabled when configuring the package before compilation.  The names
of the disabled modules are nevertheless available for use in runtime
configuration options, but they represent a ``fail-only'' functionality,
e.g. if the package was compiled without @acronym{SQL} support then
the module @samp{sql} in the above example will always fail, thus
passing the execution on to the next module.

The @code{auth} statement configures authentication and authorization.

@deffn {Configuration} authorization @var{module-list}
Define a sequence of modules to use for authorization.  Modules will
be tried in the same order as listed in @var{module-list}.

The modules available for use in authorization list are:

@table @asis
@item system
User credentials are retrieved from the system user database
(@file{/etc/password}).
@item sql
User credentials are retrieved from a @acronym{SQL} database.
A separate configuration statement, @code{sql}, is used to configure
it (@pxref{sql statement}).
@item virtdomain
User credentials are retrieved from a ``virtual domain'' user
database.  Virtual domains are configured using @code{virtdomain}
statement (@pxref{virtdomain statement}).
@item radius
User credentials are retrieved using @acronym{RADIUS}.  @xref{radius
statement}, for a detailed description on how to configure it.
@item ldap
User credentials are retrieved from an @acronym{LDAP}
database.  @xref{ldap statement}, for an information on how to
configure it.
@end table

Unless overridden by @code{authorization} statement,
the default list of authorization modules is:

@enumerate 1
@item generic
@item system
@item pam
@item sql
@item virtual
@item radius
@item ldap
@end enumerate
@end deffn

@deffn {Configuration} authentication @var{module-list}
Define a sequence of modules to use for authentication.  Modules will
be tried in the same order as listed in @var{module-list}.

The following table lists modules available for use in @var{module-list}:

@table @asis
@item generic
The generic authentication type.  User password is hashed and compared
against the hash value returned in authorization stage.
@item system
The hashed value of the user password is retrieved from
@file{/etc/shadow} file on systems that support it.
@item sql
The hashed value of the user password is retrieved from a
@acronym{SQL} database using query supplied by @code{getpass}
statement (@pxref{sql statement, getpass}).
@item pam
The user is authenticated via pluggable authentication module
(@acronym{PAM}).  The @acronym{PAM} service name to be used is
configured in @code{pam} statement (@pxref{pam statement}).
@item radius
The user is authenticated on a remote @acronym{RADIUS}
server.  @xref{radius statement}.
@item ldap
The user is authenticated using @acronym{LDAP}.  @xref{ldap statement}.
@end table

Unless overridden by @code{authentication} statement,
the list of authentication modules is the same as for
@code{authorization}, i.e.:

@enumerate 1
@item generic
@item system
@item pam
@item sql
@item virtual
@item radius
@item ldap
@end enumerate
@end deffn

@node pam statement
@subsection PAM Statement
@anchor{PAM Statement}
@kwindex pam
@subheading Syntax
@example
pam @{
  # @r{Set PAM service name.}
  service @var{text};
@}
@end example

@subheading Description
The @code{pam} statement configures @acronym{PAM} authentication.  It
contains a single sub-statement:

@deffn {Configuration} service @var{text}
Define service name to look for in @acronym{PAM} configuration.  By
default, the base name of the Mailutils binary is used.
@end deffn

This statement takes effect only if @samp{pam} is listed in
@code{authentication} statement (@pxref{auth statement}).

@node virtdomain statement
@subsection The @code{virtdomain} Statement
@anchor{Virtdomain Statement}
@kwindex virtdomain
@subheading Syntax
@example
virtdomain @{
  # @r{Name of the virtdomain password directory.}
  passwd-dir @var{dir};
@}
@end example

@subheading Description
@dfn{Virtual mail domains} make it possible to handle several
mail domains each having a separate set of users, on a single server.
The domains are completely independent of each other, i.e. the same
user name can be present in several domains and represent different
users.

When authenticating to a server with virtual domain support enabled,
users must supply their user names with domain parts.  The server strips
off the domain part and uses it as a name of UNIX-format password
database file, located in the @dfn{domain password directory}.  The
latter is set using @code{passwd-dir} statement.

@deffn {Configuration} passwd-dir @var{dir}
Set virtual domain password directory.
@end deffn

For example, when authenticating user @samp{smith@@example.com},
the server will use password file named @file{@var{dir}/example.com}.
This file must be in UNIX passwd format (@pxref{password
file,,,passwd(5), passwd(5) man page}), with encrypted passwords
stored in it (as of GNU Mailutils version @value{VERSION}, there is no
support for shadow files in virtual password directories, although
this is planned for future versions).  Here is an example record from
this file:

@example
smith:Wbld/G2Q2Le2w:1000:1000:Email Account:/var/mail/domain/smith:/dev/null
@end example

Notice, that it must contain user names without domain parts.

The @code{pw_dir} field (the 6th field) is used to determine the
location of the maildrop for this user.  It is defined as
@file{@var{pw_dir}/INBOX}.  In our example, the maildrop for user
@samp{smith} will be located in file @file{/var/mail/domain/smith}.

If user did not supply his domain name, or if no matching record was
found in the password file, or if the file matching the domain name
does not exist, then GNU Mailutils falls back to alternative method.
First, it tries to determine the IP address of the remote party.  Then
the domain name corresponding to that address is looked up in the DNS
system.  Finally, this domain name is used as a name of the password
file.

@node radius statement
@subsection The @code{radius} Statement
@anchor{Radius Statement}
@kwindex radius
@subheading Syntax
@example
radius @{
  # Set radius configuration directory.
  directory @var{dir};
  # @r{Radius request for authorization.}
  auth @var{request};
  # @r{Radius request for getpwnam.}
  getpwnam @var{request};
  # Radius request for getpwuid.
  getpwuid @var{request};
@}
@end example
@subheading Description
The @code{radius} block statement configures @acronym{RADIUS
authentication} and authorization.

Mailutils uses GNU Radius library, which is configured via
@file{raddb/client.conf} file (@pxref{client, Client Configuration,
Client Configuration, radius, GNU Radius Reference Manual}).  Its exact
location depends on configuration settings that were used while
compiling GNU Radius.  Usually it is @file{/usr/local/etc}, or
@file{/etc}.  This default can also be changed at run time using
@code{directory} statement:

@deffn {Configuration} directory @var{dir}
Set full path name to the GNU Radius configuration directory.
@end deffn

It authorization is used, the Radius dictionary file must declare the
the following attributes:

@multitable @columnfractions 0.4 0.2 0.4
@headitem Attribute    @tab Type    @tab Description
@kwindex GNU-MU-User-Name
@item GNU-MU-User-Name @tab string  @tab User login name
@kwindex GNU-MU-UID
@item GNU-MU-UID       @tab integer @tab UID
@kwindex GNU-MU-GID
@item GNU-MU-GID       @tab integer @tab GID
@kwindex GNU-MU-GECOS
@item GNU-MU-GECOS     @tab string  @tab GECOS
@kwindex GNU-MU-Dir
@item GNU-MU-Dir       @tab string  @tab Home directory
@kwindex GNU-MU-Shell
@item GNU-MU-Shell     @tab string  @tab User shell
@kwindex GNU-MU-Mailbox
@item GNU-MU-Mailbox   @tab string  @tab User mailbox
@kwindex GNU-MU-Quota
@item GNU-MU-Quota     @tab integer @tab Mail quota (in bytes)
@end multitable

@flindex mailutils.dict
A dictionary file with appropriate definitions is included in the
Mailutils distribution: @file{examples/config/mailutils.dict}.  This
file is not installed by default, you will have to manually copy it to
the GNU Radius @file{raddb/dict} directory and include it in the main
dictionary file @file{raddb/dictionary} by adding the following
statement:

@example
$INCLUDE dict/mailutils.dict
@end example

Requests to use for authentication and authorization are
configured using three statements: @code{auth}, @code{getpwnam} and
@code{getpwuid}.  Each statement takes a single argument: a string,
containing a comma-separated list of assignments.  An assignment
specifies a particular @dfn{attribute-value pair} (@pxref{Overview,
RADIUS Attributes,, radius, GNU Radius Reference Manual}) to send to
the server.  The left-hand side of the assignment is a symbolic attribute
name, as defined in one of Radius dictionaries (@pxref{dictionary
file, Dictionary of Attributes,, radius, GNU Radius Reference
Manual}).  The value is specified by the right-hand side of
assignment.  For example:

@example
"Service-Type = Authenticate-Only, NAS-Identifier = \"mail\""
@end example

The assignment may contain references to the following variables
(@pxref{Variables}):

@table @asis
@item user
The actual user name (for @code{auth} and @code{getpwnam}), or user ID
(for @code{getpwuid}).  For example:

@example
User-Name = $@{user@}
@end example

@item passwd
User password.  For examples:
@example
User-Password = $@{passwd@}
@end example
@end table

@deffn {Configuration} auth @var{pairlist}
Specifies the request to be sent to authenticate the user.  For example:

@example
auth "User-Name = $@{user@}, User-Password = $@{passwd@}";
@end example

The user is authenticated only if this request returns
@code{Access-Accept} (@pxref{Authentication Requests, Access-Accept,,
radius, GNU Radius Reference Manual}).  Any returned attribute-value
pairs are ignored. 
@end deffn

@deffn {Configuration} getpwnam @var{pairlist}
Specifies the request that returns user information for the
given user name.  For example:

@example
getpwnam "User-Name = $@{user@}, State = getpwnam, "
         "Service-Type = Authenticate-Only";
@end example

If the requested user account exists, the Radius server must return
@code{Access-Accept} packet with the following attributes:
@code{GNU-MU-User-Name}, @code{GNU-MU-UID}, @code{GNU-MU-GID},
@code{GNU-MU-GECOS}, @code{GNU-MU-Dir}, @code{GNU-MU-Shell}.

The attributes @code{GNU-MU-Mailbox} and @code{GNU-MU-Quota} are
optional.

If @code{GNU-MU-Mailbox} is present, it must contain a
valid mailbox @acronym{URL} (@pxref{Mailbox, URL}).  If
@code{GNU-MU-Mailbox} is not present, Mailutils constructs the
mailbox name using the settings from the @code{mailbox} configuration
statement (@pxref{Mailbox Statement}), or built-in defaults, if it is
not present.

If @code{GNU-MU-Quota} is present, it specifies the maximum mailbox
size for this user, in bytes.  In the absence of this attribute, 
mailbox size is unlimited.
@end deffn

@deffn {Configuration} getpwuid @var{pairlist}
Specifies the request that returns user information for the
given user ID.  In @var{pairlist}, the @samp{user} macro-variable is
expanded to the numeric value of ID.  For example:

@example
getpwuid "User-Name = $@{user@}, State = getpwuid, "
         "Service-Type = Authenticate-Only";
@end example

The reply to @code{getpwuid} request is the same as to @code{getpwnam}
request (see above).
@end deffn

@node sql statement
@subsection The @code{sql} Statement
@anchor{SQL Statement}
@kwindex sql
@subheading Syntax
@example
sql @{
  # @r{Set SQL interface to use.}
  interface @samp{mysql|odbc|postgres};
  # @r{SQL server host name.}
  host @var{arg};
  # @r{SQL user name.}
  user @var{arg};
  # @r{Password for the SQL user.}
  passwd @var{arg};
  # @r{SQL server port.}
  port @var{arg};
  # @r{Database name.}
  db @var{arg};
  # @r{Type of password returned by getpass query.}
  password-type @samp{plain | hash | scrambled};
  # @r{Set a field-map for parsing SQL replies.}
  field-map @var{list};
  # @r{SQL query returning the user's password.}
  getpass @var{query};
  # @r{SQL query to use for getpwnam requests.}
  getpwnam @var{query};
  # @r{SQL query to use for getpwuid requests.}
  getpwuid @var{query};
@}
@end example
@subheading Description

The @code{sql} statement configures access credentials to
@acronym{SQL} database and the queries for authentication and
authorization.

GNU Mailutils supports three types of @acronym{SQL} interfaces:
MySQL, PostgreSQL and ODBC.  The latter is a standard API for using
database management systems, which can be used to communicate with a
wide variety of DBMS.

@deffn {Configuration} interface @var{type}
Configures type of DBMS interface.  Allowed values for @var{type} are:

@table @asis
@item mysql
Interface with a MySQL server (@uref{http://www.mysql.org}).

@item odbc
Use ODBC interface.  See @uref{http://www.unixodbc.org}, for a detailed
description of ODBC configuration.

@item postgres
Interface with a PostgreSQL server (@uref{http://www.postgres.org}).
@end table
@end deffn

The database and database access credentials are configured using the
following statements:

@deffn {Configuration} host @var{arg}
The host running the @acronym{SQL} server.  The value can be either a
host name or an IP address in dotted-quad notation, in which case an
@acronym{INET} connection is used, or a full pathname to a file, in
which case a connection to @acronym{UNIX} socket is used.
@end deffn

@deffn {Configuration} port @var{arg}
TCP port the server is listening on (for @acronym{INET}
connections).  This parameter is optional.  Its default value depends on
the type of database being used.
@end deffn

@deffn {Configuration} db @var{arg};
Name of the database.
@end deffn

@deffn {Configuration} user @var{arg}
@acronym{SQL} user name.
@end deffn
  
@deffn {Configuration} passwd @var{arg};
Password to access the database.
@end deffn

@deffn {Configuration} password-encryption @var{arg};
Defines type of encryption used by the password returned by
@code{getpass} query (see below).  Possible arguments are:

@table @asis
@item plain
Password is in plain text.

@item crypt
@itemx hash
Password is encrypted by system @code{crypt} function
(@pxref{crypt,,,crypt(3), crypt(3) man page}).

@item scrambled
Password is encrypted by MySQL @code{password} function.
@end table
@end deffn

@deffn {Configuration} getpwnam @var{query}
Defines SQL query that returns information about the given user.  The
@var{query} is subject to variable expansion (@pxref{Variables}).  The
only variable defined is @samp{$user}, which expands to the user name.

@anchor{getpw column names}
The query should return a single row with the following columns:

@table @asis
@item name
User name.
@item passwd
User password.
@item uid
UID of the user.
@item gid
GID of the primary group.
@item gecos
Textual description of the user.
@item dir
User's home directory
@item shell
User's shell program.
@end table

The following columns are optional:

@table @asis
@item mailbox
Full pathname of the user's mailbox.  If not returned or NULL, the
mailbox is determined using the default algorithm (@pxref{Mailbox}).
@item quota
Upper limit on the size of the mailbox.  The value is either an
integer number optionally followed by one of the usual size suffixes:
@samp{K}, @samp{M}, @samp{G}, or @samp{T} (case-insensitive).
@end table
@end deffn

@deffn {Configuration} getpwuid @var{query}
Defines SQL query that returns information about the given UID.  The
@var{query} is subject to variable expansion (@pxref{Variables}).  The
only variable defined is @samp{$user}, which expands to the UID.

The query should return a single row, as described for @code{getpwnam}.
@end deffn

@deffn {Configuration} getpass @var{query}
Defines SQL query that returns the password of the given user.  The
@var{query} is subject to variable expansion (@pxref{Variables}).  The
only variable defined is @samp{$user}, which expands to the user name.

The query should return a row with a single column, which gives the
password.  The password can be encrypted as specified by the
@code{password-encryption} statement.
@end deffn

@deffn {Configuration} field-map @var{list}
Defines a translation map for column names.   The @var{list} is a
list of mappings.  Each mapping is a string
@samp{@var{name}=@var{column}}, where @var{name} is one of the names
described in @ref{getpw column names}, and @var{column} is the name of
the column in the returned row that should be used instead.  The effect of
this statement is similar to that of SQL @code{AS} keyword.  E.g. the
statement

@example
field-map (uid=user_id);
@end example

@noindent
has the same effect as using @samp{SELECT user_id AS uid} in the SQL
statement.
@end deffn

@node ldap statement
@subsection The @code{ldap} Statement
@anchor{LDAP Statement}
@kwindex ldap
@subheading Syntax
@example
ldap @{
  # @r{Enable LDAP lookups.}
  enable @var{bool};
  # @r{Set URL of the LDAP server.}
  url @var{url};
  # @r{Base DN for LDAP lookups.}
  base @var{string};
  # @r{DN for accessing LDAP database.}
  binddn @var{string};
  # @r{Password for use with binddn.}
  passwd @var{string};
  # @r{Use TLS encryption.}
  tls @var{bool};
  # @r{Set LDAP debugging level.}
  debug @var{number};
  # @r{Set a field-map for parsing LDAP replies.}
  field-map @var{list};
  # @r{LDAP filter to use for getpwnam requests.}
  getpwnam @var{string};
  # @r{LDAP filter to use for getpwuid requests.}
  getpwuid @var{filter};
@}
@end example
@subheading Description
The @code{ldap} statement configures the use of LDAP for authentication.

@deffn {Configuration} enable @var{bool}
Enables LDAP lookups.  If absent, @samp{enable On} is assumed.
@end deffn

@deffn {Configuration} url @var{url}
Sets the URL of the LDAP server.
@end deffn

@deffn {Configuration} base @var{string}
Defines base DN for LDAP lookups.
@end deffn

@deffn {Configuration} binddn @var{string}
Defines the DN for accessing LDAP database.
@end deffn

@deffn {Configuration} passwd @var{string}
Password for use when binding to the database.
@end deffn

@deffn {Configuration} tls @var{bool}
Enable the use of TLS when connecting to the server.
@end deffn

@deffn {Configuration} debug @var{number}
Set LDAP debug level.  Please refer to the OpenLDAP documentation, for
allowed @var{number} values and their meaning.
@end deffn

@deffn {Configuration} field-map @var{map} 
Defines a map for parsing LDAP replies.  The @var{map} is a list
of mappings@footnote{For backward compatibility, @var{map} can be a
string containing colon-delimited list of mappings.  Such usage is,
however, deprecated.}.  Each mapping is @samp{@var{field}=@var{attr}}, where
@var{attr} is the name of the LDAP attribute and @var{field} is a
field name that declares what information that attribute carries.
Available values for @var{field} are:

@table @asis
@item name
User name.
@item passwd
User password.
@item uid
UID of the user.
@item gid
GID of the primary group.
@item gecos
Textual description of the user.
@item dir
User's home directory
@item shell
User's shell program.
@end table

The default mapping is

@example
@group
  ("name=uid",
   "passwd=userPassword",
   "uid=uidNumber",
   "gid=gidNumber",
   "gecos=gecos",
   "dir=homeDirectory",
   "shell=loginShell")
@end group
@end example
@end deffn

@deffn {Configuration} getpwnam @var{string}
Defines the LDAP filter to use for @samp{getpwnam} requests.  The
default is:

@example
  (&(objectClass=posixAccount) (uid=$user))
@end example
@end deffn

@deffn {Configuration} getpwuid @var{string}
Defines the LDAP filter to use for @samp{getpwuid} requests.  The
default filter is:

@example
  (&(objectClass=posixAccount) (uidNumber=$user))
@end example
@end deffn

@node tls statement
@subsection The @code{tls} Statement
@anchor{TLS Statement}
@kwindex tls
@subheading Syntax
@example
tls @{
  # @r{Specify SSL certificate file.}
  ssl-certificate-file @var{string};
  # @r{Specify SSL certificate key file.}
  ssl-key-file @var{file};
  # @r{Specify trusted CAs file.}
  ssl-ca-file @var{file};
  # @r{Set the priorities to use on the ciphers, methods, etc.}
  ssl-priorities @var{string};
  # @r{Set timeout for I/O operations during TLS handshake (seconds).}
  handshake-timeout @var{n};
@}
@end example
@subheading Description

The @samp{tls} statement configures TLS parameters to be used by
servers.  It can appear both in the global scope and in server
scope.  Global tls settings are applied for servers that are declared
as supporting TLS encryption, but lack the @samp{tls} substatement.

@deffn {Configuration} ssl-certificate-file @var{string}
Specify SSL certificate file.
@end deffn

@deffn {Configuration} ssl-key-file @var{file}
Specify SSL certificate key file.
@end deffn

@deffn {Configuration} ssl-ca-file @var{file}
Specify the trusted certificate authorities file.
@end deffn

@deffn {Configuration} ssl-priorities @var{string}
Set the priorities to use on the ciphers, key exchange methods, MACs
and compression methods.
@end deffn

@deffn {Configuration} handshake-timeout @var{n}
Set the timeout (in seconds) for I/O operations during TLS handshake.
Default value is 10 seconds.
@end deffn

@node tls-file-checks statement
@subsection The @code{tls-file-checks} Statement
@kwindex tls-file-checks
@subheading Syntax
@example
tls-file-checks @{
  # @r{Configure safety checks for SSL key file.}
  key-file @var{list};
  # @r{Configure safety checks for SSL certificate.}
  cert-file @var{list};
  # @r{Configure safety checks for SSL CA file.}
  ca-file @var{list};
@}
@end example

@subheading Description

This section configures security checks applied to the particular SSL
configuration files in order to decide whether it is safe to use them.

@deffn {Configuration} key-file @var{list}
Configure safety checks for SSL key file.  Elements of the @var{list} are
names of individual checks, optionally prefixed with @samp{+} to enable or 
@samp{-} to disable the corresponding check.  Valid check names are:

@table @asis
@item none
Disable all checks.
@item all
Enable all checks.
@item gwrfil
Forbid group writable files.
@item awrfil
Forbid world writable files.
@item grdfil
Forbid group readable files.
@item ardfil
Forbid world writable files.
@item linkwrdir
Forbid symbolic links in group or world writable directories.
@item gwrdir
Forbid files in group writable directories.
@item awrdir
Forbid files in world writable directories,
@end table
@end deffn

@deffn {Configuration} cert-file @var{list}
Configure safety checks for SSL certificate.  See
@code{key-file} for a description of @var{list}.
@end deffn

@deffn {Configuration} ca-file @var{list}
Configure safety checks for SSL CA file.  See
@code{key-file} for a description of @var{list}.
@end deffn


@node gsasl statement
@subsection The @code{gsasl} Statement
@anchor{GSASL Statement}
@WRITEME
@kwindex gsasl
@subheading Syntax
@example
gsasl @{
  # @r{Name of GSASL password file.}
  cram-passwd @var{file};
  # @r{SASL service name.}
  service @var{string};
  # @r{SASL realm name.}
  realm @var{string};
  # @r{SASL host name.}
  hostname @var{string};
  # @r{Anonymous user name.}
  anonymous-user @var{string};
@}
@end example

@c -------------------------------------------------------------------

@node debugging
@section Debugging
@command{Mailutils} debugging output is controlled by a set of levels, each of
which can be set independently of others.  Each debug level consists of
a @dfn{category name}, which identifies the part of
@command{Mailutils} for which additional debugging is desired, and a
level number, which tells @command{Mailutils} how verbose should its
output be.

Valid debug levels are:

@table @asis
@item error
Displays error conditions which are normally not reported, but passed
to the caller layers for handling.
@item trace0 through trace9
Ten levels of verbosity, @samp{trace0} producing less output,
@samp{trace9} producing the maximum amount of output.
@item prot
Displays network protocol interaction, where applicable.
@end table

Implementation and applicability of each level differs between various
categories.  The full list of categories is available in 
file @file{libmailutils/diag/debcat} in the Mailutils source tree.
Most useful categories and levels implemented for them are discussed
later in this article.

@menu
* Level Syntax::
* Level BNF::
* Debugging Categories::
@end menu

@node Level Syntax
@subsection Level Syntax

Debug levels can be set either from the command line, by using the
@option{--debug-level} command line option, or from the configuration
file, using the @samp{.debug.level} statement.  In both cases, the
level is specified as a list of individual levels, delimited with
semicolons.  Each individual level can be specified as:

@table @asis
@item !@var{category}
Disables all levels for the specified @var{category}.
@item @var{category}
Enables all levels for the specified @var{category}.
@item @var{category}.@var{level}
For the given @var{category}, enables all levels from @samp{error} to
@var{level}, inclusive.
@item @var{category}.=@var{level}
Enables only the given @var{level} for this @var{category}.
@item @var{category}.!@var{level}
Disables all levels from @samp{error} to @var{level}, inclusive, for
this @var{category}.
@item @var{category}.!=@var{level}
Disables only the given @var{level} in this @var{category}.
@item @var{category}.@var{levelA}-@var{levelB}
Enables all levels in the range from @var{levelA} to @var{levelB}, inclusive.
@item @var{category}.!@var{levelA}-@var{levelB}
Disables all levels in the range from @var{levelA} to @var{levelB}, inclusive.
@end table

Additionally, a comma-separated list of level specifications is
allowed after the dot.  For example, the following specification:

@example
acl.prot,!=trace9,!trace2
@end example

enables in category @samp{acl} all levels, except @samp{trace9},
@samp{trace0}, @samp{trace1}, and @samp{trace2}.

@node Level BNF
@subsection BNF

The following specification in Backus-Naur form describes formally the
Mailutils debug level:

@example
<debug-spec> ::= <level-spec> | <debug-level-list>
<debug-level-list> ::= <debug-level> |
                       <debug-level-list> ";" <debug-level>
<debug-level> ::= <category> | "!" <category> |
                  <category> "." <level-list>
<level-list> ::= <level-spec> | <level-list> "," <level-spec>
<level-spec> ::=  <level> | <negate-level>
<negate-level> ::= "!" <level>
<level> ::= <level-number> | "=" <level-number> |
            <level-number> "-" <level-number>
<level-number> ::= "error" | "trace0" | "trace1" | "trace2" | "trace3" |
                   "trace4" | "trace5" | "trace6" | "trace7" |
                   "trace8" | "trace9" | "prot"
@end example

@node Debugging Categories
@subsection Debugging Categories

@table @asis
@item acl
This category enables debugging of Access Control Lists.  Available
levels are:

@table @asis
@item error
As usual, displays errors, not directly reported otherwise.
@item trace0
Basic tracing of ACL processing.
@item trace9
Traces the process of matching the ACL conditions.
@end table

@item config
This category affects configuration parser and/or lexical
analyzer.  The following levels are supported:

@table @asis
@item trace0
Minimal information about configuration statements.
@item trace2
Trace lexical structure of the configuration files.
@item trace7
Trace execution of the configuration parser.
@end table

Due to its specific nature, this category cannot be enabled from the
configuration file.  A special hook is provided to facilitate
debugging the configuration parser, namely, a pragmatic comment in
form: 

@example
#debug=@var{debug-level-list}
@end example

causes @var{debug-level-list} to be parsed as described above.  Thus, to
force debugging of the configuration parser, one would add the following
line at the very beginning of the configuration file: 

@example
#debug=config.trace7
@end example

@item mailbox
Operations over mailboxes.  This module supports the following levels:
@samp{error}, @samp{trace0}, @samp{trace1}, and @samp{prot}.  The
latter is used by remote mailbox support libraries.

@item auth
Enables debugging information about authentication and authorization.
This category supports the following levels: @samp{error},
@samp{trace0}, @samp{trace1}, and @samp{trace2}. 

In level @samp{trace0}, user data are reported along with the
@dfn{data source} they were obtained from.  The output may look like this:

@example
pop3d: source=system, name=gray, passwd=x, uid=120, gid=100,
gecos=Sergey Poznyakoff, dir=/home/gray, shell=/bin/bash,
mailbox=/var/mail/gray, quota=0, change_uid=1
@end example

In the @samp{trace1} level, additional flow traces are displayed.

In the level @samp{trace2}, a detailed flow trace is displayed, which
looks like the following:

@example
pop3d: Trying generic...
pop3d: generic yields 38=Function not implemented
pop3d: Trying system...
pop3d: system yields 0=Success
pop3d: Trying generic...
pop3d: generic yields 4135=Authentication failed
pop3d: Trying system...
pop3d: system yields 0=Success
@end example

@item mailer
Debugs mailer operations.  The following levels are supported: 

@table @asis
@item error
Displays mild error conditions.
@item trace0
Traces mailer operations in general: displays what part of the message
is being sent, etc.
@item trace6
When used together with @samp{prot}, displays security-sensitive
information (such as passwords, user keys, etc). in plaintext.  By
default, such information is replaced with asterisks to reduce the
possibility of security compromise.
@item trace7
When used together with @samp{prot}, displays the @dfn{payload}
information as it is being sent.  The @dfn{payload} is the actual
message contents, i.e. the part of SMTP transaction that goes after
the @samp{DATA} command and which ends with a terminating dot line.
Setting this level can generate huge amounts of information. 
@item prot
For SMTP mailer: outputs transcripts of SMTP sessions.
@end table

@emph{Note:} Unless in a very secure environment, it is advised to
avoid using level settings such as mailer.prot or mailer (without
explicit level part), because the resulting output tends to be
extremely copious and reveals sender private and security-sensitive
data.  If you wish to trace SMTP session flow, use @samp{mailer.=prot}
or at least @samp{mailer.prot,!trace6}. 

@item server
This category provides debugging information for Mailutils IP
server objects.  It supports the @samp{error} and @samp{trace0} levels. 

@item folder
This category controls debugging information shown for operations
related to Mailutils folders. 

@item remote
The remote category is used by @command{imap4d} and @command{pop3d}
servers to request showing additional information in the session
transcripts.  This category takes effect only when the @code{transcript}
configuration variable is set.  Valid levels are:

@table @asis
@item trace6
Show security-sensitive information (user passwords, etc.)
@item trace7
Show payload information
@end table
@end table

@node frm and from
@section @command{frm} and @command{from} --- List Headers from a Mailbox
@include programs/frm.texi

@page
@node mail
@section @command{mail} --- Send and Receive Mail
@include programs/mail.texi

@page
@node messages
@section @command{messages} --- Count the Number of Messages in a Mailbox
@include programs/messages.texi

@page
@node movemail
@section @command{movemail} --- Moves Mail from the User Maildrop to the Local File
@include programs/movemail.texi

@page
@node readmsg
@section @command{readmsg} --- Extract Messages from a Folder
@include programs/readmsg.texi

@page
@node decodemail
@section @command{decodemail} -- Decode multipart messages
@include programs/decodemail.texi

@node sieve
@section @command{sieve}
@include programs/sieve.texi

@c ***********************************************************************
@page
@node guimb
@section @command{guimb} --- A Mailbox Scanning and Processing Language
@include programs/guimb.texi

@page
@node mda
@section mda
@include programs/mda.texi

@page
@node lmtpd
@section lmtpd
@include programs/lmtpd.texi

@page
@node putmail
@section putmail
@include programs/putmail.texi

@page
@node mimeview
@section mimeview
@include programs/mimeview.texi

@page
@node pop3d
@section POP3 Daemon
@include programs/pop3d.texi

@page
@node imap4d
@section IMAP4 Daemon
@include programs/imap4d.texi

@page
@node comsatd
@section Comsat Daemon
@include programs/comsatd.texi

@page
@node mh
@section MH --- The MH Message Handling System
@include mu-mh.texi

@page
@node mailutils
@section mailutils
@include programs/mailutils.texi

@page
@node dotlock
@section dotlock
@include programs/dotlock.texi