@c This is part of the GNU Mailutils manual.
@c Copyright (C) 1999,2000,2001 Free Software Foundation, Inc.
@c See file mailutils.texi for copying conditions.
@comment *******************************************************************

GNU Mailutils provides a set of programs for handling the email.

@menu
* authentication:: Authorization and authentication principles.        
* configuration:: Common configuration file.
* imap4d::        IMAP4 daemon.
* pop3d::         POP3 daemon.
* frm::           List headers from a mailbox.
* mail::          Send and receive mail.
* mail.local::    Deliver mail to the local mailbox.
* messages::      Count the number of messages in a mailbox.
* readmsg::       Extract messages from a folder.
* sieve::         Mail filtering utility.
* guimb::         Mailbox scanning and processing language.
* comsatd::       Comsat daemon.
@end menu

@page
@node authentication
@section Authorization and authentication principles.        
@cindex authorization
@cindex authentication

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
either a one of them succeeds or the list is exhausted. In 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.

We represent the module lists as column-separated lists of module
names. 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 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 the @acronym{sql} database. The set
of @option{--sql-} options (@pxref{auth}) is used to configure
access to the database.
@item virtdomain
User credentials are retrieved from a ``virtual domain'' user
database.
@end table

The modules available for use in authentication list are:

@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 the @acronym{sql}
database using query supplied by @option{--sql-getpass} option
(@pxref{auth}).
@item pam
The user is authenticated via pluggable authentication module
(@acronym{pam}). The @acronym{pam} service name to be used is
configured via @option{--pam-service} option (@pxref{auth})
@end table

Unless overridden by @option{--authentication} command line option,
the list of authentication modules is:

@example
        generic:system:pam:sql
@end example

@noindent
Unless overridden by @option{--authorization} command line option,
the list of authorization modules is:

@example
        system:sql:virtdomains
@end example

@page
@node configuration
@section Mailutils configuration file
@cindex Mailutils configuration file
@cindex mailutils.rc

There are some command line options that are used so often that it is
inconvenient to specify them in the command line each time you run
a mailutils utility. The @dfn{configuration files} provide a way to
add default command line arguments without having to type them in
the command line. Upon startup, each mailutils utility scans and
processes the contents of the three startup files, none of which
are required to exist:

@enumerate
@item
the site-wide configuration file

@file{mailutils.rc}, found in your your system configuration directory
(usually @file{/etc} or @file{/usr/local/etc}).

@item
the user-specific configuration file

Usually @file{~/.mailutils}, unless @file{~/.mailutils} is a directory,
in which case @file{~/.mailutils/mailutils} is used.

@item
the programs-specific configuration file

Usually @file{~/.mu.@var{program}rc}, unless @file{~/.mailutils} is a
directory, in which case @file{~/.mailutils/@var{program}rc} is used
(where @var{program} means the program name).

@end enumerate

These files have simple line-oriented syntax. Comments begin with the
pound sign (@samp{#}) and extend through the end of the line
@footnote{If @samp{#} is not the first character on the line, it
should be separated from the previous word by any amount of whitespace.}.
Very long lines may be split across several lines by escaping final newline
with a backslash (@samp{\}) character.

In the non-program-specific configuration files, any configuration line
must start with a @dfn{tag}. In the program-specific configuration
file the tag must not be present, all options are for that specific
program.

A tag is either a name of a particular mailutils utility or @dfn{option
group}, prefixed with colon (@samp{:}). The command line options common for
several mailutils programs are divided into @dfn{option groups} or
@dfn{capabilities}, e.g. the options @option{--mail-spool} and
@option{--lock-flags} form group @samp{mailbox}. These groups are discussed
in detail below.

When processing the non-program-specific configuration files,
a mailutils utility selects
those lines whose tag is either the name of that utility or the name
of the option group supported by it. In the program-specific configuration
file, all lines are selected. For each line found, its tag (if present)
is stripped away, and the rest of the line is split up into words.
These words are regarded as command line options and are inserted to
the program arguments @emph{before} any options from the command line.
Thus the options from @file{.mailutils} take precedence over those
from @file{mailutils.rc}, and the options from the command line take
precedence over those from all three configuration files.

The word splitting occurs at whitespace characters and is similar to
that performed by the shell. If an option must contain embedded
whitespace, it should be enclosed in a pair of quotes (either double
or single quotes).

@menu
* default::        Options understood by most GNU utilities.
* mailbox::        Specifies the mail spool location, and locking strategy.
* address::        Specifies the default email address and domain.
* daemon::         Options common for daemon programs.
* auth::           Authentication-specific options.
* logging::        Logging control options.
* config sample::  A sample configuration file.
@end menu

@node default
@subsection default --- Options understood by most GNU utilities.

Each program also understands the following informational options:

@table @option
@item -u
@itemx --usage
Display a short usage message and exit.
@item -h
@itemx --help
Display help message and exit.
@item -L
@itemx --license
Display GNU General Public License and exit.
@item -v
@itemx --version
Display program version and exit.
@end table

@node mailbox
@subsection mailbox --- Specifies the mail spool location, and locking strategy.
@cindex :mailbox

Option group @samp{mailbox} consists of options used to specify the
location of the mail spool, and the locking strategy.

@table @option
@item -m @var{path}
@itemx --mail-spool=@var{path}
Set path to the mailspool directory
@item --lock-flags=@var{flags}
Set the default mailbox lock flags (E=external, R=retry, T=time, P=pid).
@end table

@node address
@subsection address --- Specifies the default email address and domain.
@cindex :address

Option group @samp{address} consists of options used to specify how to
qualify email addresses.

An unqualified address (one without an @var{@@}) is qualified by appending
@var{@@}@var{defaultdomain}. @var{defaultdomain} is the return of
gethostname(), or the result of gethostbyname() on the return of
gethostname() (if the DNS lookup is successful).

If the email address of the current user is needed, either the address set by
--email-addr is returned, or the current uid is looked up in the user
database, and qualified with the @var{defaultdomain}.

@table @option
@item -E @var{email}
@itemx --email-addr=@var{email}
Set the current user's email address, this it makes more sense to use
this in one of the per-user configuration files.
@item -D @var{domain}
@itemx --email-domain=@var{domain}
Set the default email domain, this might make sense to use in either
the global or one of the per-user configuration files.
@end table

@node daemon
@subsection daemon --- Options common for daemon programs.
@cindex :daemon

@table @option
@item -d[@var{number}]
@itemx --daemon[=@var{number}]
Run in standalone mode. An optional @var{number} specifies the maximum number
of child processes the daemon is allowed to fork. When it is omitted,
it defaults to 20 processes.
@emph{Please note}, that there should be no whitespace between the
@option{-d} and its parameter.
@item -i
@itemx --inetd
Run in inetd mode.
@item -p @var{number}
@itemx --port @var{number}
Listen on given port @var{number}. This option is meaningful only in
standalone mode. It defaults to port 143.
@item -t @var{number}
@itemx --timeout @var{number}
Set idle timeout to given @var{number} of seconds. The daemon breaks the
connection if it receives no commands from the client within that number
of seconds.
@end table

@node auth
@subsection auth --- Authentication-specific options.
@cindex :auth

These options control the authorization and authentication module
lists. For a description of auhtentication concepts, refer to
@xref{authentication}.

@table @option
@item --authorization @var{modlist}

This option allows to set up a list of modules to be used for
authorization. @var{modlist} is a colon-separated list of
modules. Valid modules are:

@table @asis
@item system
User credentials are retrieved from the system user database
(@file{/etc/password}).
@item sql
User credentials are retrieved from the @acronym{sql} database. The set
of @option{--sql-} options (see below) is used to configure
access to the database.
@item virtdomain
User credentials are retrieved from a ``virtual domain'' user
database.
@end table

@item --authentication @var{modlist}

This option allows to set up a list of modules to be used for
authentication. @var{modlist} is a colon-separated list of
modules. Valid modules are:

@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 the @acronym{sql}
database using query supplied by @option{--sql-getpass} option
(see below).
@item pam
The user is authenicated via pluggable authentication module
(@acronym{pam}). The @acronym{pam} service name to be used is
configured via @option{--pam-service} option (see below)
@end table

@item --pam-service @var{name}
When compiled with @acronym{pam} support, this option specifies the
name of @acronym{pam} service to be used when authenticating.
@end table

The following options exist in this group if the package was configured
with @option{--enable-sql} option. They take effect only if the
@samp{sql} module is used in authentication and/or authorization.
Currently only MySQL is supported.  

@table @option
@item --sql-getpwnam @var{query}
@acronym{sql} query to retrieve a passwd entry based on username
@item --sql-getpwuid @var{query} 
@item --sql-getpass @var{query}
@acronym{sql} query to retrieve a password from the database
@item --sql-host @var{name}
Name or IP of MySQL server to connect to.
@item --sql-user @var{name}
@acronym{sql} user name
@item --sql-passwd @var{string}
@acronym{sql} connection password
@item --sql-db @var{string}
Name of the database to connect to.
@item --sql-port @var{number}
Port to use
@end table

@node logging
@subsection logging --- Logging control options.
@cindex :logging

@table @option
@item log-facility @var{facility}
Output logs to the specified @command{syslog} facility. The following
facility names are recognized: @samp{user}, @samp{daemon}, @samp{mail},
@samp{auth} and @samp{local0} through @samp{local7}. These names are
case-insensitive.
@end table

@node config sample
@subsection A sample configuration file.
@cindex mailutils.rc, an example

The following configuration file specifies that all mailutils programs
should use @file{/var/spool/mail} as a local mailspool
directory. Programs performing authentication will use @acronym{pam}
service @samp{mailutils}. All programs, except @command{imap4d} will
issue log messages via @samp{mail} facility, @command{imap4d} will use
facility @samp{local1}.

@example
@group
:mailbox --mail-spool /var/spool/mail
:auth --authentication pam --pam-service mailutils
:logging --log-facility mail
imap4d --daemon=20 --timeout=1800 --log-facility local1
@end group
@end example 

@page
@node imap4d
@section IMAP4 daemon
@pindex imap4d

GNU imap4d is a daemon implementing @sc{imap4} rev1 protocol for
accessing and handling electronic mail messages on a server. It can
be run either as a standalone program or from @file{inetd.conf} file.

@menu
* Namespace::       Imap4d namespace.
* Starting imap4d:: Invocation options.
@end menu

@node Namespace
@subsection Imap4d Namespace
@cindex namespace
@cindex IMAP4 namespace

GNU imap4d supports a notion of @dfn{namespaces} defined in RFC 2342. A
namespace is a set of directories upon which the user has certain
permissions. It should be understood that these persmissions apply
only if the underlying filesystem allows them.

The three namespaces supported by @command{imap4d} are:

@table @asis
@item Personal Namespace
A namespace that is within the personal scope of the authenticated user
on a particular connection. The user has all permissions on this namespace.

@item Other Users' Namespace
A namespace that consists of mailboxes from the ``Personal Namespaces''
of other users. The user can read and list mailboxes from this
namespace. However, he is not allowed to use @samp{%} and @samp{*}
wildcards with @command{LIST} command, that is he can access a
mailbox only if he knows exactly its location.

@item Shared Namespace
A namespace that consists of mailboxes that are intended to be shared
amongst users and do not exist within a user's Personal Namespace.
The user has all permissions on this namespace.

@end table

@noindent
By default, @command{imap4d} starts with the following namespaces:

@table @asis
@item Personal Namespace
The home directory of the user, if exists.

@item Other Users' Namespace
Empty
@item Shared Namespace
Empty
@end table

@emph{Note}, that this means that by default, a user won't be able to
see or otherwise access mailboxes residing in the directories other than
his own home.

To change these defaults, use @option{--shared-namespace} and
@option{--other-namespace} options.

@node Starting imap4d
@subsection Starting imap4d

@command{imap4d} may run either in @dfn{standalone} or in @dfn{inetd}
operation modes. When run in ``standalone'' mode, the server disconnects
from the terminal and runs as a daemon, forking a child for each new
connection.

The ``inetd'' mode allows to start the server from
@file{/etc/inetd.conf} file. This is the default operation mode. 

@example
imap4  stream tcp nowait  root  /usr/local/sbin/imap4d imap4d
@end example


The program uses following option groups: @xref{mailbox},
@xref{daemon}, @xref{logging}, @xref{auth}.

@subheading Command line options

@table @option
@item -d[@var{number}]
@itemx --daemon[=@var{number}]
Run in standalone mode. An optional @var{number} specifies the maximum number
of child processes the daemon is allowed to fork. When it is omitted,
it defaults to 20 processes.
@emph{Please note}, that there should be no whitespace between the
@option{-d} and its parameter.
@item -h
@itemx --help
Display short help message and exit.
@item -i
@itemx --inetd
Run in inetd mode.
@item -m @var{path}
@itemx --mail-spool=@var{path}
Set path to the mailspool directory
@item -O @var{pathlist}
@itemx --other-namespace=@var{pathlist}
Set the list of directories forming the ``Other User's'' namespace.
@var{pathlist} is a list of directory names separated by colons.
@item -p @var{number}
@itemx --port @var{number}
Listen on given port @var{number}. This option is meaningful only in
standalone mode. It defaults to port 143.
@item -S @var{pathlist}
@itemx --shared-namespace=@var{pathlist}
Set the list of directories, forming the ``Shared''
namespace. @var{pathlist} is a list of directory names separated by colons.
@item -t @var{number}
@itemx --timeout @var{number}
Set idle timeout to given @var{number} of seconds. Default is 1800 seconds (30
minutes).  The daemon breaks the connection if it receives no commands
from the client within that number of seconds.
@item -v
@itemx --version
Display program version and exit.
@end table

@page
@node pop3d
@section POP3 daemon
@pindex pop3d

The @command{pop3d} daemon implements the Post Office Protocol server.

pop3d has two operation modes:

@table @asis
@item Inetd
The server is started from @file{/etc/inetd.conf} file:

@example
pop3  stream tcp nowait  root  /usr/local/sbin/pop3d pop3d
@end example

This is the default operation mode.

@item Standalone
The server runs as daemon, forking a child for each new connection. This
mode is triggered by @option{-d} command line switch.
@end table

The program uses following option groups: @xref{mailbox},
@xref{daemon}, @xref{logging}, @xref{auth}.

@subheading Command line options

@table @option
@item -d[@var{number}]
@itemx --daemon[=@var{number}]
Run in standalone mode. An optional @var{number} specifies the maximum number
of child processes the daemon is allowed to fork. When it is omitted,
it defaults to 10 processes.
@emph{Please note}, that there should be no whitespace between the
@option{-d} and its parameter.
@item -h
@itemx --help
Display short help message and exit.
@item -i
@itemx --inetd
Run in inetd mode.
@item -m @var{path}
@itemx --mail-spool=@var{path}
Set path to the mailspool directory
@item -p @var{number}
@itemx --port @var{number}
Listen on given port @var{number}. This option is meaningful only in
standalone mode. It defaults to port 110.
@item -t @var{number}
@itemx --timeout @var{number}
Set idle timeout to given @var{number} of seconds. Default is 600 seconds (10
minutes).  The daemon breaks the connection if it receives no commands
from the client within that number of seconds.
@item -v
@itemx --version
Display program version and exit.
@end table

@page
@node frm
@section frm --- List headers from a mailbox.
@pindex frm

The @command{frm} command outputs a header information of
the selected messages in a mailbox. By default, @command{frm} reads the
user's system mailbox and outputs the contents of @code{From} and
@code{Subject} headers for each message. If a folder is specified in
the command line, the program reads that folder rather than the default
mailbox.

The program uses following option groups: @xref{mailbox}.

The following command line options alter the behavior of the program:

@table @option
@item -f STRING
@item --field STRING
Display the header named by STRING instead of @code{From} @code{Subject} pair.
@item -l
@itemx --to
Include the contents of @code{To} header to the output. The output field
order is then: @code{To} @code{From} @code{Subject}.
@item -n
@itemx --number
Prefix each line with corresponding message number.
@item -Q
@itemx --Quiet
Be very quiet. Nothing is output except error messages. This is useful
in shell scripts where only the return status of the program is
important.
@item -q
@itemx --query
Print a message only if there are unread messages in the mailbox.
@item -S
@itemx --summary
Print a summary line.
@item -s ATTR
@itemx --status ATTR
Only display headers from messages with the given status.
ATTR may be one of the following: @samp{new}, @samp{read},
@samp{unread}. It is sufficient to specify only first letter of
an ATTR. Multiple @option{-s} options are allowed.
@item -t
@itemx --align
Tidy mode. Currently is not implemented. Included for compatibility with
@command{frm} program from Elm package.
@end table

@page
@node mail
@section mail ---  send and receive mail.
@pindex mail

@command{Mail} is an enhanced version of standard @command{/bin/mail} program.
As well as its predecessor, it can be used either in sending mode or
in reading mode. @command{Mail} enters sending mode when one or more
email addresses were specified in this command line. In this mode the
program waits until user finishes composing the message, then attempts
to send it to the specified addresses and exits.
See @ref{Composing Mail}, for a detailed description of this behavior.

If the command line contained no email addresses, @command{mail} switches
to reading mode. In this mode it allows to read and manipulate the
contents of a mailbox. The URL of the mailbox to operate upon is
taken from the argument of @option{--file} command line option. If it
is not specified, the user's system mailbox is assumed. For more
detail, see @ref{Reading Mail}.

@menu
* Invoking Mail::            Command line options.
* Specifying Messages::      How to specify message sets.
* Composing Mail::           Composing mail.
* Reading Mail::             Reading mail.
* Mail Variables::           How to alter the behavior of mail.
* Mail Configuration Files:: Personal and system-wide configuration files.
@end menu

@node Invoking Mail
@subsection Command line options

General usage of @command{mail} program is:

@example
      mail [OPTION...] [address...]
@end example
@noindent
If [address...] part is present, @command{mail} switches to mail sending
mode, otherwise it operates in mail reading mode.

The program uses following option groups: @xref{mailbox}.

@command{Mail} understands following command line options:

@table @option
@item -e
@itemx --exist
Return true if the mailbox contains some messages. Return false
otherwise.
This is useful for writing shell scripts.
@item -f[FILE]
@itemx --file[=FILE]
Operate on mailbox FILE. If this option is not specified, the default
is user's system mailbox. If it is specified without argument, the
default is $HOME/mbox.
@emph{Please note}, that there should be no whitespace between the
short variant of the option (@option{-f}), and its parameter. Similarly,
when using long option (@option{--file}), its argument must be preceded by
equal sign.
@item -F
@itemx --byname
Save messages according to sender. Currently this option is not implemented.
@item -H
@itemx --headers
Print header summary to stdout and exit.
@item -i
@itemx --ignore
Ignore interrupts.
@item -m @var{path}
@itemx --mail-spool=@var{path}
Set path to the mailspool directory
@item -n
@itemx --norc
Do not read the system-wide mailrc file. @xref{Mail Configuration Files}.
@item -N
@itemx --nosum
Do not display initial header summary.
@item -p
@itemx --print
@itemx -r
@itemx --read
Print all mail to standard output. It is equivalent to issuing following
commands after starting @samp{mail -N}:

@example
 print *
 quit
@end example
@item -q
@itemx --quit
Cause interrupts to terminate program.
@item -s SUBJ
@itemx --subject=SUBJ
Send a message with a Subject of SUBJ. Valid only in sending mode.
@item -t
@itemx --to
Switch to sending mode.
@item -u USER
@itemx --user=USER
Operate on USER's mailbox. This is equivalent to:

@example
        mail -f/@var{spool_path}/USER
@end example
@noindent
with @var{spool_path} being the full path to your mailspool directory
@*(@file{/var/spool/mail} or @file{/var/mail} on most systems).
@item -?
@itemx --help
Display a help message.
@itemx --usage
Display a short usage summary.
@item -V
@itemx --version
Print program version and exit.
@end table

@node Specifying Messages
@subsection How to specify message sets

Many mail commands such as print and delete can be given a @dfn{message list}
to operate upon. Wherever the message list is omitted, the command
operates on the current message.

The @dfn{message list} in its simplest form is one of:

@table @asis
@item .
Selects current message. It is equivalent to empty message list.
@item *
Selects all messages in the mailbox.
@item ^
Selects first non-deleted message.
@item $
Selects last non-deleted message.
@end table

In its complex form, the @dfn{message list} is a comma or whitespace-separated
list of @dfn{message specifiers}. A @dfn{message specifier} is one
of

@table @asis
@item Message Number
This specifier addresses the message with the given ordinal number
in the mailbox.
@item Message range
@dfn{Message range} is specified as two message numbers separated by
a dash. It selects all messages with the number lying within that range.
@item Attribute specifier
An @dfn{Attribute specifier} is a colon followed by a single
letter. The @dfn{Attribute specifier} addresses all messages in the
mailbox that have the given attribute. These are the valid attribute
specifiers:

@table @samp
@item :d
Selects all deleted messages.
@item :n
Selects all recent messages, i.e. the messages that have not been
neither read not seen so far.
@item :o
Selects all messages that have been seen.
@item :r
Selects all messages that have been read.
@item :u
Selects all messages that have @emph{not} been read.
@item :t
Selects all tagged messages (@pxref{Marking Messages}).
@item :T
Selects all untagged messages.
@end table
@item Header match
The @dfn{header match} is a string in the form:

@example
[@var{header}:]/@var{string}/
@end example
@noindent

It selects all messages that contain header field @var{header}
matching given @var{regexp}. If the variable @code{regexp} is set,
the @var{string} is assumed to be a POSIX regexp. Otherwise, a
header is considered to match @var{string} if the latter constitutes
a substring of the former (comparison is case-insensitive).

If @var{header}: part is omitted, it is assumed to be @samp{Subject:}.
@item Message body match
The @dfn{message body match} is a string in the form:

@example
:/@var{string}/
@end example
@noindent

It selects all messages whose body matches the string. The matching
rules are the same as described under ``Header match''.

@end table

A @dfn{message specifier} can be followed by @dfn{message part
specifier}, enclosed in a pair of brackets. A @dfn{message part
specifier} controls which part of a message should be operated upon.
It is meaningful only for multipart messages. A @dfn{message part
specifier} is a comma or whitespace - separated list of part numbers
or ranges. Each part number can in turn be @dfn{message part specifier},
thus allowing for operating upon multiply-encoded messages.

The following are the examples of valid message lists:



@node Composing Mail
@subsection Composing mail

You can compose the message by simply typing the contents of it, line
by line. But usually this is not enough, you would need to edit
your text, to quote some messages, etc. @command{Mail} provides these
capabilities through @dfn{compose escapes}. The @dfn{compose escapes}
are single-character commands, preceded by special @dfn{escape character},
which defaults to @samp{~}. The combination @code{escape character + command}
is recognized as a compose escape only if it occurs at the beginning of
a line. If the escape character must appear at the beginning of a
line, enter it twice.
The actual escape character may be changed by setting the value of
@code{escape} mail variable (@pxref{Mail Variables}).

@menu
* Quitting Compose Mode::
* Getting Help on Compose Escapes::
* Editing the Message::
* Modifying the Headers::
* Enclosing Another Message::
* Adding a File to the Message::
* Printing And Saving the Message::
* Signing the Message::
* Printing Another Message::
* Inserting Value of a Mail Variable::
* Executing Other Mail Commands::
* Executing Shell Commands::
@end menu

@node Quitting Compose Mode
@subsubsection Quitting Compose Mode

There are several commands allowing you to quit the compose mode.

Typing the end-of-file character (@samp{C-D}) on a line alone finishes
compose mode and sends the message to its destination. The @samp{C-D}
character looses its special meaning if @code{ignoreeof} mail variable
is set.

If mail variable @code{dot} is set, typing dot (@samp{.}) on a line
alone achieves the same effect as @samp{C-D} above.

Finally, using @samp{~.} escape always quits compose mode and sends
out the composed message.

To abort composing of a message without sending it, type interrupt
character (by default, @samp{C-C}) twice. This behavior is disabled
when mail variable @code{ignore} is set. In this case, you can use
@samp{~x} escape to achieve the same effect.

@node Getting Help on Compose Escapes
@subsubsection Getting Help on Compose Escapes: ~?

The @samp{~?} escape prints on screen a brief summary of the available
compose escapes. @emph{Please note}, that @samp{~h} escape prompts
for changing the header values, and does @emph{not} give help.

@node Editing the Message
@subsubsection Editing the Message: ~e and ~v.

If you are not satisfied with the message as it is, you can edit it
using a text editor specified either by @code{EDITOR} or by
@code{VISUAL} environment variables. The @samp{~e} uses the former,
and @samp{~v} uses the latter.

By default both escapes allow you to edit only the body of the
message. However, if the @code{editheaders} variable is set,
@command{mail} will load into the editor the complete text of
the message with headers included, thus allowing you to change
the headers as well.

@node Modifying the Headers
@subsubsection Modifying the Headers: ~h, ~t, ~c, ~b, ~s

To add new addresses to the list of message recipients, use @samp{~t}
command, e.g.:

@example
~t name1@@domain.net name2
@end example

To add addresses to @code{Cc} or @code{Bcc}, use @samp{~c} or @samp{~b}
escapes respectively.

To change the @code{Subject} header, use @samp{~s} escape, e.g.:

@example
~s "Re: your message"
@end example

Finally, to edit all headers, type @samp{~h} escape. This will present
you with the values of @code{To}, @code{Cc}, @code{Bcc}, and
@code{Subject} headers allowing to edit them with normal text editing
commands.

@node Enclosing Another Message
@subsubsection Enclosing Another Message: ~m and ~M

If you are sending mail from within mail command mode, you can enclose
the contents of any message sent to you by using @samp{~m} or @samp{~M}
commands. Typing @samp{~m} alone will enclose the contents of the
current message, typing @samp{~m 12} will enclose the contents of
message #12 and so on.

The @samp{~m} uses retained and ignored lists when enclosing headers,
the @samp{~M} encloses all header fields
(@pxref{Controlling Header Display}).

In both cases, the contents of @code{indentprefix} mail variable is
prepended to each line enclosed.

@node Adding a File to the Message
@subsubsection Adding a File to the Message: ~r and ~d

To append the contents of file @var{filename} to the message, type

@example
~r @var{filename}
@end example
@noindent
or

@example
~< @var{filename}
@end example
@noindent

The @samp{~d} escape is a shorthand for

@example
~r dead.letter
@end example

@node Printing And Saving the Message
@subsubsection Printing And Saving the Message

The @samp{~p} escape types the contents of the message entered so far,
including headers, on your terminal. You can save the message to
an arbitrary file using @samp{~w} escape. It takes the filename as its
argument.

@node Signing the Message
@subsubsection Signing the Message: ~a and ~A

To save you the effort of typing your signature at the end of each
message, you can use @samp{~a} or @samp{~A} escapes. If your signature
occupies one line only, save it to the variable @code{sign} and use
@samp{~a} escape to insert it. Otherwise, if it is longer than one
line, save it to a file, store the name of this file in the
variable @code{Sign}, and use @samp{~A} escape to insert it into
the message.

@node Printing Another Message
@subsubsection Printing Another Message: ~f and ~F

Sometimes it is necessary to view the contents of another message,
while composing. These two escapes allow it. Both take the message
list as their argument. If they are used without argument, the
contents of the current message is printed. The difference between
@samp{~f} and @samp{~F} is that the former uses ignored and retained
lists to select headers to be displayed, whereas the latter prints
all headers (@pxref{Controlling Header Display}).

@node Inserting Value of a Mail Variable
@subsubsection Inserting Value of a Mail Variable: ~i

The @samp{~i} escape enters the value of the named mail variable into
the body of the message being composed.

@node Executing Other Mail Commands
@subsubsection Executing Other Mail Commands: ~: and ~-

You can execute a mail command from within compose mode using @samp{~:}
or @samp{~-} escapes. For example, typing

@example
~: from :t
@end example
@noindent

will display the from lines of all tagged messages. Note, that executing
mail-sending commands (@pxref{Replying}) from within the compose mode is
not allowed. An attempt to execute such a command will result in
diagnostic message ``Command not allowed in an escape sequence'' being
displayed. Also, when starting compose mode immediately from the shell
(e.g. running @samp{mail address@@domain}), most mail commands are
meaningless, since there is no mailbox to operate upon. In this case,
the only commands that can reasonably be used are: @code{alias},
@code{unalias}, @code{alternate}, @code{set}, and @code{unset}.


@node Executing Shell Commands
@subsubsection Executing Shell Commands: ~! and ~|

The @samp{~!} escape executes specified command and returns you to
@command{mail} compose mode without altering your message. When used without
arguments, it starts your login shell. The @samp{~|} escape pipes the
message composed so far through the given shell command and replaces the
message with the output the command produced. If the command produced
no output, @command{mail} assumes that something went wrong and retains
the old contents of your message.

@c *********************************************************************

@node Reading Mail
@subsection Reading mail

To read messages from a given mailbox, use one of the following ways of
invoking @command{mail}:

@table @code
@item mail
To read messages from your system mailbox.
@item mail --file
To read messages from your mailbox ($HOME/mbox).
@item mail --file=@var{path_to_mailbox}
To read messages from the specified mailbox.
@item mail --user=@var{user}
To read messages from the system mailbox belonging to @var{user}.
@end table

@emph{Please note}, that usual mailbox permissions won't allow you
to use the last variant of invocation, unless you are a super-user.
Similarly, the last but one variant is also greatly affected by the
permissions the target mailbox has.

Unless you have started mail with @option{--norc} command line option,
it will read the contents of the system-wide configuration file.
Then it reads the contents of user configuration file, if any.
For detailed description of these files, see @ref{Mail Configuration Files}.
After this initial setup, @command{mail} displays the first page of header
lines and enters interactive mode. In interactive mode, @command{mail}
displays its prompt (@samp{?}, if not set otherwise) and executes the
commands the user enters.

@menu
* Quitting the Program::
* Obtaining Online Help::
* Moving Within a Mailbox::
* Changing mailbox/directory::
* Controlling Header Display::
* Displaying Information::
* Displaying Messages::
* Marking Messages::
* Disposing of Messages::
* Saving Messages::
* Editing Messages::
* Scripting::
* Aliasing::
* Replying::
* Incorporating New Mail::
* Shell Escapes::
@end menu

@c **********************************
@node Quitting the Program
@subsubsection Quitting the program

Following commands quit the program:

@table @samp
@item quit
Terminates the session. If @command{mail} was operating upon user's system
mailbox, then all undeleted and unsaved messages that have been read and
are not marked with hold flag are saved to the user's mbox file
(@file{$HOME/mbox}). The messages, marked with @code{delete} are removed.
The program exits to the Shell, unless saving the mailbox fails, in
which case user can escape with the exit command.

@item exit
@itemx ex
@itemx xit
Program exits to the Shell without modifying the mailbox it operates
upon.
@end table

Typing EOF (@samp{C-D}) alone is equivalent to @samp{quit}.

@node Obtaining Online Help
@subsubsection Obtaining online help

Following commands can be used during the session to request online
help:

@table @samp
@item help [@var{command}]
@itemx hel [@var{command}]
@itemx ? [@var{command}]
Display detailed command synopsis. If no @var{command} is given, help for
all available commands is displayed.
@item list
@itemx *
Print a list of available commands.
@item version
@itemx ve
Display program version.
@item warranty
@itemx wa
Display program warranty statement.
@end table

@node Moving Within a Mailbox
@subsubsection Moving within a mailbox

@table @samp
@item next
@itemx n
Move to the next message.
@item previous
@itemx prev
Move to the previous message.
@end table

@node Changing mailbox/directory
@subsubsection Changing mailbox/directory

@table @samp
@item cd [@var{dir}]
@itemx chdir [@var{dir}]
@itemx ch [@var{dir}]
Change to the specified directory. If @var{dir} is omitted, $HOME is
assumed.
@item file [@var{mailbox}]
@itemx fi [@var{mailbox}]
@itemx folder [@var{mailbox}]
@itemx fold [@var{mailbox}]
Read in the contents of the specified @var{mailbox}. The current mailbox
is updated as if @code{quit} command has been issued.
If @var{mailbox} is omitted, the command prints the current mailbox
name followed by the summary information regarding it, e.g.:

@example
& fold
"/var/spool/mail/gray": 23 messages 22 unread
@end example
@end table

@node Controlling Header Display
@subsubsection Controlling header display

To control which headers in the message should be displayed, @command{mail}
keeps two lists: a @dfn{retained} header list and an @dfn{ignored}
header list. If @dfn{retained} header list is not empty, only the
header fields listed in it are displayed when printing the message.
Otherwise, if @dfn{ignored} header list is not empty, only the headers
@emph{not listed} in this list are displayed. The uppercase variants
of message-displaying commands can be used to print all the headers.

The following commands modify and display the contents of both lists.

@table @samp
@item discard [@var{header-field-list}]
@itemx di [@var{header-field-list}]
@itemx ignore [@var{header-field-list}]
@itemx ig [@var{header-field-list}]
Add @var{header-field-list} to the ignored list. When used without
arguments, this command prints the contents of ignored list.
@item retain [@var{header-field-list}]
@itemx ret [@var{header-field-list}]
Add @var{header-field-list} to the retained list. When used without
arguments, this command prints the contents of retained list.
@end table

@node Displaying Information
@subsubsection Displaying information

@table @samp
@item =
Displays the current message number.
@item headers [@var{msglist}]
@itemx h [@var{msglist}]
Lists the current pageful of headers.
@item from [@var{msglist}]
@itemx f [@var{msglist}]
Lists the contents of @samp{From} headers for a given set of messages.
@item z [@var{arg}]
Presents message headers in pagefuls as described for @code{headers}
command. When @var{arg} is @samp{.}, it is generally equivalent to
@code{headers}. When @var{arg} is omitted or is @samp{+}, the next
pageful of headers is displayed. If @var{arg} is @samp{-}, the
previous pageful of headers is displayed. The latter two forms
of @code{z} command may also take a numerical argument meaning the
number of pages to skip before displaying the headers. For
example:

@example
& z +2
@end example
@noindent
will skip two pages of messages before displaying the header summary.
@item size [@var{msglist}]
@itemx si [@var{msglist}]
Lists the message number and message size in bytes for each message in
@var{msglist}.
@item folders
Displays the value of @code{folder} variable.
@item summary
@itemx su
Displays current mailbox summary. E.g.:

@example
& summary
"/var/spool/mail/gray": 23 messages 22 unread
@end example
@end table

@node Displaying Messages
@subsubsection Displaying messages

@table @samp
@item print [@var{msglist}]
@itemx p [@var{msglist}]
@item type [@var{msglist}]
@itemx t [@var{msglist}]
Prints out the messages from @var{msglist}. The variable @code{crt}
determines the minimum number of lines the body of the message must
contain in order to be piped through pager command specified
by environment variable @code{PAGER}. If @code{crt} is set to a numeric
value, this value is taken as the mininmum number of lines. Otherwise,
if @code{crt} is set without a value then the height of the terminal
 screen is used to compute the threshold.  The number of lines on
screen is controlled by @code{screen} variable.
@item Print [@var{msglist}]
@itemx P [@var{msglist}]
@itemx Type [@var{msglist}]
@itemx T [@var{msglist}]
Like print but also prints out ignored header fields.
For detailed description of ignored header lists, see @ref{Controlling Header Display}.
@item decode [@var{msglist}]
@itemx dec [@var{msglist}]
Print a multipart message. The @code{decode} command decodes and prints
out specified message parts. E.g.
@example
& decode 15[2]
+---------------------------------------
| Message=15[2]
| Type=message/delivery-status
| encoding=7bit
+---------------------------------------
Content-Type: message/delivery-status
...
@end example
@item top [@var{msglist}]
@itemx to [@var{msglist}]
Prints the top few lines of each message in @var{msglist}.  The number
of lines printed is controlled by the variable @code{toplines} and
defaults to five.
@item pipe [@var{msglist}] [@var{shell-command}]
@itemx | [@var{msglist}] [@var{shell-command}]
Pipe the contents of specified messages through @var{shell-command}. If
@var{shell-command} is empty but the string variable @code{cmd} is set,
the value of this variable is used as a command name.
@end table

@node Marking Messages
@subsubsection Marking messages

@table @samp
@item tag [@var{msglist}]
@itemx ta [@var{msglist}]
Tag messages. The tagged messages can be referred to in message list
using @samp{:t} notation.
@item untag [@var{msglist}]
@itemx unt [@var{msglist}]
Clear tags from specified messages. To untag all messages tagged so far
type
@example
& untag :t
@end example
@item hold [@var{msglist}]
@itemx ho [@var{msglist}]
@itemx preserve [@var{msglist}]
@itemx pre [@var{msglist}]
Marks each message to be held in user's system mailbox. This command
does not override the effect of @code{delete} command.
@end table

@node Disposing of Messages
@subsubsection Disposing of messages

@table @samp
@item delete [@var{msglist}]
@itemx d [@var{msglist}]
Mark messages as deleted. Upon exiting with @code{quit} command these
messages will be deleted from the mailbox. Until the end of current
session the deleted messages can be referred to in message lists using
:d notation.
@item undelete [@var{msglist}]
@itemx u [@var{msglist}]
Clear delete mark from the specified messages.
@item dp [@var{msglist}]
@itemx dt [@var{msglist}]
Deletes the current message and prints the next message. If
@var{msglist} is specified, deletes all messages from the list and
prints the message, immediately following last deleted one.
@end table

@node Saving Messages
@subsubsection Saving messages

@table @samp
@item save [[@var{msglist}] @var{file}]
@itemx s [[@var{msglist}] @var{file}]
Takes a message list and a file name and appends each message in turn to
the end of the file. The name of file and number of characters appended
to it is echoed on the terminal. Each saved message is marked for
deletion as if with @code{delete} command, unless the variable
@code{keepsave} is set.
@item Save [@var{msglist}]
@itemx S [@var{msglist}]
Like @code{save}, but the file to append messages to is named after the
sender of the first message in @var{msglist}. For example:

@example
@group
& from 14 15
 U  14 smith@@noldor.org Fri Jun 30 18:11  14/358   The Save c
 U  15 gray@@noldor.org  Fri Jun 30 18:30  8/245    Re: The Sa
& Save 14 15
"smith" 22/603
@end group
@end example
@noindent

i.e., 22 lines (603 characters) have been appended to the file ``smith''.
If the file does not exist, it is created.

@item write [[@var{msglist}] @var{file}]
@itemx w [[@var{msglist}] @var{file}]
Similar to @code{save}, except that only message body (without the
header) is saved.
@item Write [@var{msglist}]
@itemx W [@var{msglist}]
Similar to @code{Save}, except that only message body (without the
header) is saved.
@item mbox [@var{msglist}]
@itemx mb [@var{msglist}]
@itemx touch [@var{msglist}]
@itemx tou [@var{msglist}]
Mark list of messages to be saved in the user's mailbox ($HOME/mbox)
upon exiting via @code{quit} command. This is the default action for
all read messages, unless you have variable @code{hold} set.
@item copy [[@var{msglist}] @var{file}]
@itemx c [[@var{msglist}] @var{file}]
Similar to @code{save}, except that saved messages are not marked for
deletion.
@item Copy [@var{msglist}]
@itemx C [@var{msglist}]
Similar to @code{Save}, except that saved messages are not marked for
deletion.
@end table

@node Editing Messages
@subsubsection Editing messages

These command allow to edit messages in a mailbox. @emph{Please note},
that modified messages currently do not replace original ones. i.e.
you have to save them explicitly using your editor's @code{save}
command if you do not want the effects of your editing to be lost.

@table @samp
@item edit [@var{msglist}]
@itemx e [@var{msglist}]
Edits each message in @var{msglist} with the editor, specified in
@code{EDITOR} environment variable.
@item visual [@var{msglist}]
@itemx v [@var{msglist}]
Edits each message in @var{msglist} with the editor, specified in
@code{VISUAL} environment variable.
@end table

@node Scripting
@subsubsection Scripting

@subheading Comments
The @samp{#} character introduces an end-of-line comment. All characters
until and including the end of line are ignored.

@subheading Displaying arbitrary text
The @samp{echo} (@samp{ec}) command prints its arguments to stdout.

@subheading Sourcing external command files
The command @samp{source @var{filename}} reads commands from the named
file. Its minimal abbreviation is @samp{so}.

@subheading Setting and unsetting the variables.

The mail variables may be set using @samp{set} (@samp{se}) command. The
command takes a list of assignments. The syntax of an assignment is

@table @samp
@item @var{name}=@var{string}
Assign a string value to the variable. If @var{string} contains
whitespace characters it must be enclosed in a pair of
double-quote characters (@samp{"})
@item @var{name}=@var{number}
Assign a numeric value to the variable.
@item @var{name}
Assign boolean @code{True} value.
@item no@var{name}
Assign boolean @code{False} value.
@end table

Example:

@example
& set askcc nocrt indentprefix="> "
@end example
@noindent

This statement sets @code{askcc} to @code{True}, @code{crt} to
@code{False}, and @code{indentprefix} to ``> ''.

To unset mail variables use @samp{unset}(@samp{uns}) command. The
command takes a list of variable names to unset.

Example:
To undo the effect of the previous example, do:

@example
& unset askcc crt indentprefix
@end example

@subheading Setting and unsetting shell environment variables.

Shell environment may be modified using @samp{setenv} (@samp{sete})
command. The command takes a list of assignments. The syntax of an
assignment is:

@table @samp
@item @var{name}=@var{value}
If variable @var{name} does not already exist in the environment,
then it is added to the environment with the value @var{value}.
If @var{name} does exist, then its value in the environment is
changed to @var{value}. 
@item @var{name}
Delete the variable @var{name} from the environment (``unset'' it).
@end table

@subheading Conditional statements

The conditional statement allows to execute a set of mail commands
depending on the mode the @command{mail} program is in. The conditional
statement is:

@example
if @var{cond}
...
else
...
endif
@end example
@noindent

where @samp{...} represents the set of commands to be executed in each
branch of the statement. @var{cond} can be one of the following:

@table @samp
@item s
True if @command{mail} is operating in mail sending mode.
@item r
True if @command{mail} is operating in mail reading mode.
@item t
True if stdout is a terminal device (as opposed to a regular file).
@end table

The conditional statements can be nested to arbitrary depth. The minimal
abbreviations for @samp{if}, @samp{else} and @samp{endif} commands are
@samp{i}, @samp{el} and @samp{en}.

Example:

@example
if t
set crt prompt="& "
else
unset prompt
endif
if s
alt gray@@farlep.net gray@@mirddin.farlep.net
set
@end example

@node Aliasing
@subsubsection Aliasing

@table @samp
@item alias [alias [address...]]
@itemx a [alias [address...]]
@itemx group [alias [address...]]
@itemx g [alias [address...]]
With no arguments, prints out all currently-defined aliases.
With one argument, prints out that alias.
With more than one argument, creates a new alias or changes an old one.
@item unalias [alias...]
@itemx una [alias...]
Takes a list of names defined by alias commands and discards the
remembered groups of users.  The alias names no longer have any
significance.
@item alternates name...
@itemx alt name...
The alternates command is useful if you have accounts on several
machines. It can be used to inform mail that the listed addresses are
really you.  When you reply to messages, mail will not send a copy of
the message to any of the addresses listed on the alternates list.
If the alternates command is given with no argument, the current set of
alternate names is displayed.
@end table

@node Replying
@subsubsection Replying

@table @samp
@item mail [address...]
@itemx m [address...]
Switches to compose mode. After composing the message, sends messages to
the specified addresses.

@item reply [@var{msglist}]
@itemx respond [@var{msglist}]
@itemx r [@var{msglist}]

For each message in @var{msglist}, switches to compose mode and sends
the composed message to the sender and all recipients of the message.

@item Reply [@var{msglist}]
@itemx Respond [@var{msglist}]
@itemx R [@var{msglist}]

Like @code{reply}, except that the composed message is sent only to
originators of the specified messages.

@item followup [@var{msglist}]
@itemx fo [@var{msglist}]

Switches to compose mode. After composing, sends the message to the
originators and recipients of all messages in @var{msglist}.

@item Followup [@var{msglist}]
@itemx F [@var{msglist}]

Similar to @code{followup}, but reply message is sent only to
originators of messages in @var{msglist}.
@end table

@node Incorporating New Mail
@subsubsection Incorporating new mail

The @code{incorporate} (@code{inc}) command incorporates newly arrived
messages to the displayed list of messages. This is done automatically
before returning to @command{mail} command prompt if the variable
@code{autoinc} is set.

@node Shell Escapes
@subsubsection Shell escapes

To run arbitrary shell command from @command{mail} command prompt, use
@code{shell} (@code{sh}) command. If no arguments are specified, the
command starts the user login shell. Otherwise, it uses its first
argument as a file name to execute and all subsequent arguments are
passed as positional parameters to this command. The @code{shell}
command can also be spelled as @code{!}.

@c **********************************

@node Mail Variables
@subsection How to alter the behavior of mail

Following variables control the behavior of GNU @command{mail}:

@table @code
@item Sign
@*Type: String.
@*Default: Unset.

Contains the filename holding users signature. The contents of this
file is appended to the end of a message being composed by @code{~A}
escape.
@item appenddeadletter
@*Type: Boolean.
@*Default: False.

If this variable is @code{True}, the contents of canceled letter is
appended to the user's @file{dead.letter} file. Otherwise it overwrites
its contents.

@item askbcc
@*Type: Boolean.
@*Default: False.

When set to @code{True} the user will be prompted to enter @code{Bcc}
field before composing the message.

@item askcc
@*Type: Boolean.
@*Default: True.

When set to @code{True} the user will be prompted to enter @code{Cc}
field before composing the message.

@item asksub
@*Type: Boolean.
@*Default: True in interactive mode, False otherwise.

When set to @code{True} the user will be prompted to enter @code{Subject}
field before composing the message.

@item autoinc
@*Type: Boolean.
@*Default: True.

Automatically incorporate newly arrived messages.

@item autoprint
@*Type: Boolean.
@*Default: False.

Causes the delete command to behave like dp - thus, after deleting a
message, the next one will be typed automatically.

@item cmd
@*Type: String.
@*Default: Unset.

Contains default shell command for @code{pipe}.

@item columns
@*Type: Numeric.
@*Default: Detected at startup by querying the terminal device. If this
fails, the value of environment variable @code{COLUMNS} is used.

This variable contains the number of columns on terminal screen.

@item crt
@*Type: Boolean or Numeric
@*Default: True in interactive mode, False otherwise.

The variable @code{crt} determines the minimum number of lines the body
of the message must contain in order to be piped through pager command
specified by environment variable @code{PAGER}. If @code{crt} is set
to a numeric value, this value is taken as the threshold. Otherwise,
if @code{crt} is set without a value, then the height of the terminal
screen is used to compute the threshold.  The number of lines on
screen is controlled by @code{screen} variable.

@item dot
@*Type: Boolean.
@*Default: False.

If @code{True}, causes @command{mail} to interpret a period alone on a line as the
terminator of a message you are sending.

@item editheaders
@*Type: Boolean.
@*Default: False.

When set, @command{mail} will include message headers in the text to
be the @code{~e} and @code{~v} escapes, thus allowing you to customize
the headers.

@item escape
@*Type: String.
@*Default: ~

If defined, the first character of this option gives the character to
denoting escapes.

@item folder
@*Type: String.
@*Default: Unset.

The name of the directory to use for storing folders of messages. If
unset, $HOME is assumed.

@item header
@*Type: Boolean.
@*Default: True, unless started with @option{--nosum} (@option{-N}) option.

Whether to run @code{headers} command automatically after entering
interactive mode.

@item hold
@*Type: Boolean.
@*Default: False.

When set to @code{True}, the read or saved messages will be stored in
user's mailbox (@file{$HOME/mbox}). Otherwise, they will be held in
system mailbox also. This option is in effect only when operating
upon user's system mailbox.

@item ignore
@*Type: Boolean.
@*Default: False.

When set to @code{True}, @command{mail} will ignore keyboard interrupts
when composing messages. Otherwise an interrupt will be taken as a
signal to abort composing.

@item ignoreeof
@*Type: Boolean.
@*Default: False.

Controls whether typing EOF character terminates the letter being
composed.

@item indentprefix
@*Type: String.
@*Default: "\t" (a tab character).

String used by the @code{~m} tilde escape for indenting quoted messages.

@item keepsave
@*Type: Boolean.
@*Default: False.

Controls whether saved messages should be kept in system mailbox too.
This variable is in effect only when operating upon a user's system
mailbox.

@item metoo
@*Type: Boolean.
@*Default: False.

Usually, when an alias is expanded that contains the sender, the sender
is removed from the expansion.  Setting this option causes the sender to
be included in the group.

@item mode
@*Type: String.
@*Default: The name of current operation mode.

Setting this variable does not affect the operation mode of the program.

@item noregex
@*Type: Boolean.
@*Default: False.

Setting this to @code{True} enables use of regular expressions in
@samp{/.../} message specifications.

@item outfolder
@*Type: String.
@*Default: Unset.

Contains the directory in which files created by @code{save},
@code{write}, etc. commands will be stored. When unset, current
directory is assumed.

@item page
@*Type: Boolean.
@*Default: False.

If set to @code{True}, the @code{pipe} command will emit a linefeed
character after printing each message.

@item prompt
@*Type: String.
@*Default: "? "

Contains the command prompt sequence.

@item quiet
@*Type: Boolean.
@*Default: False.

When set, suppresses the output of the startup banner.

@item quit
@*Type: Boolean.
@*Default: False, unless started with @option{--quit} (@option{-q}) option.

When set, causes keyboard interrupts to terminate the program.

@item rc
@*Type: Boolean.
@*Default: True, unless started with @option{--norc} (@option{-N}) option.

When this variable is set, @command{mail} will read the system-wide
configuration file upon startup. See @ref{Mail Configuration Files}.

@item record
@*Type: String.
@*Default: Unset.

When set, any outgoing message will be saved to the named file.

@item save
@*Type: Boolean.
@*Default: True.

When set, the aborted messages will be stored in the user's
@file{dead.file}. See also @code{appenddeadletter}.

@item screen
@*Type: Numeric.
@*Default: Detected at startup by querying the terminal device. If this
fails, the value of environment variable @code{LINES} is used.

This variable contains the number of lines on terminal screen.

@item sendmail
@*Type: String.
@*Default: sendmail:/usr/lib/sendmail

Contains the URL of mail transport agent.

@item sign
@*Type: String.
@*Default: Unset.

Contains the user's signature. The contents of this variable is appended
to the end of a message being composed by @code{~a} escape. Use
@code{Sign} variable, if your signature occupies more than one line.

@item subject
@*Type: String.
@*Default: Unset.

Contains default subject line. This will be used when @code{asksub} is
off.

@item toplines
@*Type: Numeric.
@*Default: 5

Number of lines to be displayed by @code{top} and @code{Top} commands.

@item verbose
@*Type: Boolean.
@*Default: False.

When set, the actual delivery of messages is displayed on the user's terminal.
@end table

@node Mail Configuration Files
@subsection Personal and system-wide configuration files

Upon startup, @command{mail} reads the contents of the two command files:
the system-wide configuration file, and the user's configuration
file. Each line read from these files is processed like a usual
@command{mail} command.

When run with @option{--norc} (@option{-N}) option, @command{mail} does
not read the contents of system-wide configuration file. The user's
file, if it exists, is always processed.

The user's configuration file is located in the user's home
directory and is named @file{.mailrc}. The location and name of
the system-wide configuration file is determined when configuring the
package via @option{--with-mail-rc} option. It defaults to
@file{@var{sysconfdir}/mail.rc}.

@page
@node mail.local
@section mail.local --- Deliver mail to the local mailbox.
@pindex mail.local

@command{mail.local} reads the standard input up to an end-of-file
and appends the received data to the local mailboxes.

@menu
* Invocation::     Mail.local options
* MTA::            Using mail.local with various MTAs
* Mailbox Quotas:: Setting up mailbox quotas. 
* Filters::        Implementing user-defined mail filters. 
@end menu

@node Invocation
@subsection Invoking mail.local

The program uses following option groups: @xref{mailbox}, @xref{auth},
@xref{logging}.

@table @option
@item -f @var{addr}
@itemx --from @var{addr}
Specify the sender's name. This option forces @command{mail.local} to
add @samp{From } envelope to the beginning of the message. If it is
not specified, @command{mail.local} first looks into the first line
from the standard input. If it starts with @samp{From }, it is assumed
to contain a valid envelope. If it does not, @command{mail.local}
creates the envelope by using current user name and date.
@item -h
@itemx --help
Display this help and exit.
@item -L
@itemx --license
Display GNU General Public License and exit.
@item -m @var{path}
@itemx --mail-spool @var{path}
Specify path to mailspool directory.
@item -q
@itemx --quota-db @var{file}
Specify path to mailbox quota database (@pxref{Mailbox Quotas}). 
@item -s @var{pattern}
@itemx --source @var{pattern}
Set name pattern for user-defined mail filters (@pxref{Filters}). The
metacharacters @samp{%u} and @samp{%h} in the pattern are expanded to
the current recipient user name and home directory correspondingly.
@item -t @var{number}
@itemx --timeout @var{number}
Wait @var{number} seconds for acquiring the lockfile. If it doesn't
become available after that amount of time, return failure. The timeout
defaults to 5 minutes.
@item -x guile
@itemx --debug guile
Start with guile debugging evaluator and backtraces. This is convenient
for debugging user-defined filters (@pxref{Filters}).
@item -x @var{number}
@itemx --debug @var{number}
Set debugging level.
@item -v
@itemx --version
Display program version and exit.
@item --ex-multiple-delivery-success
Don't return errors when delivering to multiple recipients.
@item --ex-quota-tempfail
Return temporary failure if disk or mailbox quota is exceeded. By
default, 'service unavailable' is returned if the message exceeds
the mailbox quota.
@end table

@node MTA
@subsection Using mail.local with various MTAs

This section explains how to invoke @command{mail.local} from
configuration files of various Mail Transport Agents.

All examples in this section suppose that @command{mail.local}
must receive following command line switches:

@example
  -s %h/.filter.scm -q /etc/mail/userquota
@end example

@menu
* sendmail::    Using mail.local with sendmail.
* exim::        Using mail.local with exim.
@end menu

@node sendmail
@subsubsection Using mail.local with sendmail.

The @command{mail.local} must be invoked from the local mailer
definition in the @file{sendmail.cf} file. It must have the
following flags set @samp{lswS}, meaning the mailer is local,
the quote characters should be stripped off the address before
invoking the mailer, the user must have a valid account on this
machine and the userid should not be reset before calling the
mailer. Additionally, @samp{fn} flags may be specified to allow
@command{mail.local} to generate usual @samp{From } envelope
instead of the one supplied by sendmail.

Here is an example of mailer definition in @file{sendmail.cf}

@example 
Mlocal, P=/usr/local/libexec/mail.local,
        F=lsDFMAw5:/|@@qSPfhn9,
        S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,
        T=DNS/RFC822/X-Unix,
        A=mail -s %h/.filter.scm -q /etc/mail/userquota $u
@end example

To define local mailer in @samp{mc} source file, it will suffice to
set:

@example
define(`LOCAL_MAILER_PATH', `/usr/local/libexec/mail.local')
define(`LOCAL_MAILER_ARGS',
       `mail -s %h/.filter.scm -q /etc/mail/userquota $u')
@end example

@node exim
@subsubsection Using mail.local with exim.

Using @command{mail.local} with exim is quite straightforward. The
following example illustrates the definition of appropriate transport
and director in @file{exim.conf}:

@example
# transport
mail_local_pipe:
  driver = pipe
  command = /usr/local/libexec/mail.local -s %h/.filter.scm \
              -q /etc/mail/userquota $local_part
  return_path_add
  delivery_date_add
  envelope_to_add
  
# director
mail_local:
  driver = localuser
  transport = mail_local_pipe
@end example

@node Mailbox Quotas
@subsection Setting up mailbox quotas

@node Filters
@subsection Implementing user-defined mail filters.

@page
@node messages
@section messages --- Count the number of messages in a mailbox.
@pindex messages

@command{Messages} prints on standard output the number of messages
contained in each folder specified in command line. If no folders
are specified, it operates upon user's system mailbox. For each
folder, the following output line is produced:

@example
     Number of messages in @var{folder}: @var{number}
@end example
@noindent
where @var{folder} represents the folder name, @var{number} represents
the number of messages.

The program uses following option groups: @xref{mailbox}.

The program accepts following command line options:

@table @option
@item -q
@itemx --quite
@itemx -s
@itemx --silent
Be quiet. Display only number of messages per mailbox, without leading text.
@item -?
@itemx --help
Output help message and exit.
@item --usage
Output short usage summary and exit.
@item -V
@itemx --version
Output program version and exit.
@end table

@page
@node readmsg
@section readmsg --- Extract messages from a folder.
@pindex readmsg

The program, readmsg, extracts with the selection argument messages from
a mailbox.  Selection can be specify by:

@enumerate

@item
A lone ``*'' means select all messages in the mailbox.

@item
A list of message numbers may be specified.  Values
of  ``0''  and ``$'' in the list both mean the last
message in the mailbox.  For example:
@example
     readmsg 1 3 0
@end example
extracts  three messages from the folder:  the first, the third, and the last.

@item
Finally, the selection may be some text to match.  This  will  select  a  mail
message which exactly matches the specified text.  For example,
@example
     readmsg staff meeting
@end example
extracts the message which contains the words ``staff meeting.''  Note that it
will not match a message containing ``Staff Meeting'' - the matching  is  case
sensitive.   Normally only the first message which matches the pattern will be
printed.

@end enumerate

@subheading Command line options

@table @option

@item -a
@itemx --show-all
If a pattern is use for selection show all messages that match pattern
by default only the first one is presented.

@item -d
@itemx --debug
Display mailbox debuging information.

@item -f @var{MAILBOX}
@itemx --folder=@var{MAILBOX}
Specified the default mailbox.

@item -h
@itemx --header
Show the entire header and ignore the weedlist.

@item -n
@itemx --no-header
Do not print the message header.

@item -p
@itemx --form-feed
Put form-feed (Control-L) between messages instead of newline.

@item  -w @var{weedlist}
@itemx --weedlist=@var{weedlist}
A whitespace or coma separated list of header names to show per message.
Default is --weedlist=''From Subject Date To CC Apparently-''

@end table

@page
@node sieve
@section sieve
@pindex sieve

Sieve is a language for filtering e-mail messages at time of final
delivery, described in RFC 3028. GNU mailutils provides two
implementations of this language: a stand-alone @dfn{sieve interpreter}
and a @dfn{sieve translator and filter}. The following sections describe these
utilities in detail.

@menu
* sieve interpreter::   A Sieve Interpreter
* sieve.scm::           A Sieve to Scheme Translator and Filter
@end menu

@node sieve interpreter
@subsection A Sieve Interpreter

Sieve interpreter @command{sieve} allows to apply Sieve scripts to an
arbitrary number of mailboxes. Currently @command{sieve} supports the
following actions:

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

@subheading Invocation

The @command{sieve} invocation syntax is:

@example
        sieve [@var{options}] @var{script}
@end example

@noindent
where @var{script} denotes the filename of the sieve program to parse,
and @var{options} is one or more of the following:

@table @option
@item -c
@itemx --compile-only
Compile script and exit.

@item -d[@var{flags}]
@itemx --debug[=@var{flags}]
Specify debug flags. The @var{flags} argument is a sequence of one or
more of the following letters:

@multitable @columnfractions .40 .45
@item @samp{a} @tab Enable address parser traces
@item @samp{g} @tab Enable main parser traces
@item @samp{T} @tab Enable mailutil traces
@item @samp{P} @tab Trace network protocols
@item @samp{t} @tab Enable sieve trace 
@item @samp{h} @tab Debug sieve header filling
@item @samp{q} @tab Trace sieve message queries
@end multitable

When omitted, @var{flags} defaults to @samp{TPt}.

@item -f
@itemx --mbox-url=@var{mbox}
Mailbox to sieve (defaults to user's system mailbox)

@item -k
@itemx --keep-going
Keep on going if execution fails on a message

@item -M
@itemx --mailer-url=@var{mailer}
Override the mailer URL (defaults to "sendmail:")

@item -n
@itemx --no-actions
Dry run: do not execute any actions, just print what would be done.

@item -t @var{ticket}
@itemx --ticket=@var{ticket}
Ticket file for mailbox authentication
@end table

Apart from these, @command{sieve} understands the options from the
@code{mailbox} option group (@pxref{mailbox}).

@c ***********************************************************************

@page
@node sieve.scm
@subsection A Sieve to Scheme Translator and Filter

A Sieve to Scheme Translator @command{sieve.scm} translates a given
Sieve script into an equivalent Scheme program and optionally executes
it. The program itself is written in Scheme and requires presence of
Guile 1.4 on the system. For more information on Guile refer to
@ref{Top,,Overview,guile,The Guile Reference Manual}.

@table @option
@item -f @var{filename}
@itemx --file @var{filename}
Set input file name.

@item -o @var{filename}
@itemx --output @var{filename}
Set output file name

@item -L @var{dirname}
@itemx --lib-dir @var{dirname}
Set sieve library directory name

@item -d @var{level}
@item --debug @var{level}
Set debugging level

@end table            

The Scheme programs produced by @command{sieve.scm} can be used with
@command{guimb} or @command{mail.local}.

@c ***********************************************************************
@page
@node guimb
@section guimb --- A mailbox scanning and processing language.
@pindex guimb

@command{Guimb} is for mailboxes what @command{awk} is for text files.
It processes mailboxes, applying the user-supplied scheme procedures
to each of them in turn and saves the resulting output in mailbox
format.

The program uses following option groups: @xref{mailbox}.

@menu
* Specifying Scheme Program to Execute::
* Specifying Mailboxes to Operate Upon::
* Passing Options to Scheme::
* Guimb Invocation Summary::
* Scheme Procedures and Variables::
@end menu

@node Specifying Scheme Program to Execute
@subsection Specifying Scheme Program to Execute

The Scheme program or expression to be executed is passed to
@command{guimb} via the following options:

@table @option
@item -s @var{file}
@itemx --source @var{file}
Load Scheme source code from @var{file}.
@item -c @var{expr}
@itemx --code @var{expr}
Execute given scheme expression.
@end table

The above switches stop further argument processing, and pass all
remaining arguments as the value of @code{(command-line)}.

If the remaining arguments must be processed by @command{guimb} itself,
use following options:

@table @option
@item -e @var{expr}
@itemx --expression @var{expr}
Execute scheme expression.
@item -f @var{file}
@itemx --file @var{file}
Load Scheme source code from @var{file}.
@end table

You can specify both of them. In this case, the @var{file} is read
first, then @var{expr} is executed. You may still pass any additional
arguments to the script using @option{--guile-arg} option
(@pxref{Passing Options to Scheme}).

@node Specifying Mailboxes to Operate Upon
@subsection Specifying Mailboxes to Operate Upon

There are four basic ways of passing mailboxes to @command{guimb}.

@table @code
@item guimb [@var{options}] [@var{mailbox}...]
The resulting mailbox is not saved, unless the user-supplied
scheme program saves it.
@item guimb [@var{options}] --mailbox @var{defmbox}
The contents of @var{defmbox} is processed and is replaced with the resulting
mailbox contents. Useful for applying filters to user's mailbox.
@item guimb [@var{options}] --mailbox @var{defmbox} mailbox [mailbox...]
The contents of specified mailboxes is processed, and the resulting
mailbox contents is appended to @var{defmbox}.
@item guimb [@var{options}] --user @var{username} [mailbox...]
The contents of specified mailboxes is processed, and the resulting
mailbox contents is appended to the user's system mailbox. This allows
to use @command{guimb} as a mail delivery agent.
@end table

If no mailboxes are specified in the command line, @command{guimb} reads
and processes the system mailbox of the current user.

@node Passing Options to Scheme
@subsection Passing Options to Scheme

Sometimes it is necessary to pass some command line options to the
scheme procedure. There are three ways of doing so.

When using @option{--source} (@option{-s}) or @option{--code}
(@option{-c}) options, all the rest of the command line following
the option's argument is passed to Scheme program verbatim. This
allows for making guimb scripts executable by the shell. If your system
supports @samp{#!} magic at the start of scripts, add the following two
lines to the beginning of your script to allow for its immediate execution:

@example
#! /usr/local/bin/guimb -s
!#
@end example

@noindent
(replace @samp{/usr/local/bin/} with the actual path to the @command{guimb}).

Otherwise, if you use @option{--file} or @option{--expression} oprions,
the additional arguments may be passed to the Scheme program @option{-g}
(@option{--guile-arg}) command line option. For example:

@example
guimb --guile-arg -opt --guile-arg 24 --file progfile
@end example

In this example, the scheme procedure will see the following command line:

@example
progfile -opt 24
@end example

Finally, if there are many arguments to be passed to Scheme, it is more
convenient to enclose them in @option{-@{} and @option{-@}} escapes:

@example
guimb -@{ -opt 24 -@} --file progfile
@end example

@node Guimb Invocation Summary
@subsection Guimb Invocation Summary

This is a short summary of the command line options available to
@command{guimb}.

@table @option
@item -d
@itemx --debug
Start with debugging evaluator and backtraces.
@item -e EXPR
@itemx --expression EXPR
Execute given Scheme expression.
@item -m @var{path}
@itemx --mail-spool=@var{path}
Set path to the mailspool directory
@item -f PROGFILE
@itemx --file PROGFILE
Read Scheme program from PROGFILE.
@item -g ARG
@itemx --guile-command ARG
Append ARG to the command line passed to Scheme program.
@item -@{ ... -@}
Pass all command line options enclosed between @option{-@{} and @option{-@}}
to Scheme program.
@item -m
@itemx --mailbox MBOX
Set default mailbox name.
@item -u
@itemx --user NAME
Act as local MDA for user NAME.
@item -h
@itemx --help
Display help message.
@item  -v
@itemx --version
Display program version.
@end table

@node Scheme Procedures and Variables
@subsection Scheme Procedures and Variables

@menu
* Address Functions::
* Mailbox Functions::
* Message Functions::
* MIME Functions::
* Log Functions::
@end menu


@node Address Functions
@subsubsection Address Functions

@deffn Function mu-address-get-personal ADDRESS NUM
Return personal part of an email address.
@end deffn

@deffn Function mu-address-get-comments ADDRESS NUM
@end deffn

@deffn Function mu-address-get-email ADDRESS NUM
Return email part of an email address.
@end deffn

@deffn Function mu-address-get-domain ADDRESS NUM
Return domain part of an email address
@end deffn

@deffn Function mu-address-get-local ADDRESS NUM
Return local part of an email address.
@end deffn

@deffn Function mu-address-get-count ADDRESS
Return number of parts in email address.
@end deffn

@node Mailbox Functions
@subsubsection Mailbox Functions

@deffn Function mu-mailbox-open URL MODE
Opens a mailbox specified by URL.
@end deffn

@deffn Function mu-mailbox-close MBOX
Closes mailbox MBOX
@end deffn

@deffn Function mu-mailbox-get-url MBOX
Returns the URL of the mailbox.
@end deffn

@deffn Function mu-mailbox-get-port MBOX MODE
Returns a port associated with the contents of the MBOX.
MODE is a string defining operation mode of the stream. It may
contain any of the two characters: @samp{r} for reading, @samp{w} for
writing.
@end deffn

@deffn Function mu-mailbox-get-message MBOX MSGNO
Retrieve from MBOX message # MSGNO.
@end deffn

@deffn Function mu-mailbox-messages-count MBOX
Returns number of messages in the mailbox.
@end deffn

@deffn Function mu-mailbox-expunge MBOX
Expunges deleted messages from the mailbox.
@end deffn

@deffn Function mu-mailbox-url MBOX
Returns the URL of the mailbox
@end deffn

@deffn Function mu-mailbox-append-message MBOX MESG
Appends the message to the mailbox
@end deffn

@node Message Functions
@subsubsection Message Functions

@deffn Function mu-message-copy MESG
Creates the copy of the given message.
@end deffn

@deffn Function mu-message-set-header MESG HEADER VALUE REPLACE
Sets new VALUE to the header HEADER of the message MESG.
If the HEADER is already present in the message its value
is replaced with the supplied one if the optional REPLACE is
#t. Otherwise new header is created and appended.
@end deffn

@deffn Function mu-message-get-size MESG
Returns the size of the given message.
@end deffn

@deffn Function mu-message-get-lines MESG
Returns number of lines in the given message.
@end deffn

@deffn Function mu-message-get-sender MESG
Returns the sender email address for the message MESG.
@end deffn

@deffn Function mu-message-get-header MESG HEADER
Returns the header value of the HEADER in the MESG.
@end deffn

@deffn Function mu-message-get-header-fields MESG HEADERS
Returns the list of headers in the MESG. If optional HEADERS is
specified it should be a list of header names to restrict return
value to.
@end deffn

@deffn Function mu-message-set-header-fields MESG LIST REPLACE
Set the headers in the message MESG from LIST
LIST is a list of (cons HEADER VALUE)
Optional parameter REPLACE specifies whether the new header
values should replace the headers already present in the
message.
@end deffn

@deffn Function mu-message-delete MESG FLAG
Mark given message as deleted. Optional FLAG allows to toggle deleted mark
The message is deleted if it is #t and undeleted if it is #f
@end deffn

@deffn Function mu-message-get-flag MESG FLAG
Return value of the attribute FLAG.
@end deffn

@deffn Function mu-message-set-flag MESG FLAG VALUE
Set the given attribute of the message. If optional VALUE is #f, the
attribute is unset.
@end deffn

@deffn Function mu-message-get-user-flag MESG FLAG
Returns value of the user attribute FLAG.
@end deffn

@deffn Function mu-message-set-user-flag MESG FLAG VALUE
Set the given user attribute of the message. If optional VALUE is
#f, the attribute is unset.
@end deffn

@deffn Function mu-message-get-port MESG MODE FULL
Returns a port associated with the given MESG. MODE is a string
defining operation mode of the stream. It may contain any of the
two characters: @samp{r} for reading, @samp{w} for writing.
If optional FULL argument specified, it should be a boolean value.
If it is #t then the returned port will allow access to any
part of the message (including headers). If it is #f then the port
accesses only the message body (the default).
@end deffn

@deffn Function mu-message-get-body MESG
Returns the message body for the message MESG.
@end deffn

@deffn Function mu-message-send MESG MAILER
Sends the message MESG. Optional MAILER overrides default
mailer settings in mu-mailer.
@end deffn

@node MIME Functions
@subsubsection MIME Functions

@deffn Function mu-mime-create FLAGS MESG
Creates a new MIME object.
@end deffn

@deffn Function mu-mime-multipart? MIME
Returns #t if MIME is a multipart object.
@end deffn

@deffn Function mu-mime-get-num-parts MIME
Returns number of parts in a MIME object.
@end deffn

@deffn Function mu-mime-get-part MIME PART
Returns part number PART from a MIME object.
@end deffn

@deffn Function mu-mime-add-part MIME MESG
Adds MESG to the MIME object.
@end deffn

@deffn Function mu-mime-get-message MIME
Converts MIME object to a message.
@end deffn

@node Log Functions
@subsubsection Log Functions

@deffn Function mu-openlog IDENT OPTION FACILITY
Opens a connection to the system logger for Guile program.
@end deffn

@deffn Function mu-logger PRIO TEXT
Generates a log message to be distributed via syslogd.
@end deffn

@deffn Function mu-closelog
Closes the channel to the system logger open by mu-openlog.
@end deffn

@page
@node comsatd
@section Comsat daemon
@pindex comsatd

Comsatd is the server which receives reports of incoming mail and
notifies users, wishing to get this service. It can be started
either from @file{inetd.conf} or as a standalone daemon.

@menu
* Starting comsatd::       Invocation.
* Configuring comsatd::    Configuration of comsatd.
* dot.biffrc::             A per-user configuration file.
@end menu

@node Starting comsatd
@subsection Starting comsatd

@command{Comsatd} uses following option groups: @xref{mailbox},
@xref{daemon}, @xref{logging}.

@table @option
@item -c @var{file}
@itemx --config @var{file}
Read configuration from given @var{file}. For more information about
comsatd configuration files, see @ref{Configuring comsatd}.
@item -d
@itemx --daemon
Run as a standalone daemon.
@item -i
@itemx --inetd
The server is started from @file{/etc/inetd.conf} file:

@example
comsat dgram  udp wait  root  /usr/sbin/comsatd \
comsatd -c /etc/comsat.conf
@end example

This is the default operation mode.
@item -m @var{path}
@itemx --mail-spool=@var{path}
Set path to the mailspool directory
@item -p @var{number}
@itemx --port @var{number}
Specify the port number to listen on. Default is 512.
@item -v
@itemx --version
Output version and exit successfully.
@item -h
@itemx --help
Display short help message and exit.
@end table

@node Configuring comsatd
@subsection Configuring comsatd

The configuration parameters for comsatd are kept in a single
configuration file. The file uses line-oriented format: each line
contains a single statement. Comments are introduced with the @samp{#}
sign and empty lines are ignored. You can specify the configuration
file to use by using @option{-c} or @option{--config} command line switch.

The configuration file statements can logically be subdivided into
@dfn{General Settings}, @dfn{Security Settings} and @dfn{Access Control
Lists}. The following sections address each of these statement group in
detail.

@menu
* General Settings::
* Security Settings::
* Access Control Lists::
@end menu

@node General Settings
@subsubsection General Settings

These statements control the general behavior of the comsat daemon:

@table @asis
@item max-lines @var{number}
Set maximum number of message body lines to be output.
@item allow-biffrc ( yes | no )
Enable or disable processing of user's @file{.biffrc} file. By default,
it is enabled.
@end table

@node Security Settings
@subsubsection Security Settings

These statements control the way @command{comsatd} fights possible
flooding attacks.

@table @asis
@item max-requests @var{number}
Set maximum number of incoming requests per @samp{request-control-interval}.
@item request-control-interval @var{number}
Set the request control interval (seconds).
@item overflow-delay-time @var{number}
Set the initial amount of time to sleep, after the first overflow occurs.
@item overflow-control-interval @var{number}
Set the overflow control interval. If two consecutive overflows happen
within @var{number} seconds, the overflow-delay-time is doubled.
@end table

@node Access Control Lists
@subsubsection Access Control Lists

Access control lists determine from which addresses @command{comsatd}
will receive mail notification messages.

The access control lists are introduced in configuration file using
keyword @samp{acl}. General format for an ACL rule is

@example
acl @var{action} @var{netlist}
@end example

@noindent
Here, @var{action} specifies the action to be taken when a request
arrives from one of the networks, listed in @var{netlist}. There are
two possible actions: @samp{allow} and @samp{deny}.

The @var{netlist} is a whitespace-separated list of network numbers.
Each network number may be specified in one of the following forms:

@table @asis
@item @var{netnum}
Means a single host with IP address @var{netnum}.
@item @var{netnum}/@var{netmask}
@item @var{netnum}/@var{masklen}
@item @samp{any}
Denotes any IP address. It is equivalent to @samp{0.0.0.0/0}.
@end table

Upon receiving a notification message, @command{comsatd} compares its
source address against each ACL rule in the order of their appearance
in the configuration file. The first rule that matches the packet
determines whether the message will be processed or rejected. If
no matching rule was found, the default rule applies. Currently, default
rule is

@example
acl allow any
@end example

@noindent
If you don't need such behavior, specify the default rule explicitly.
For example, the common use would be:

@example
@group
acl allow 127.0.0.1
acl deny any
@end group
@end example

@noindent
which makes @command{comsatd} receive the notification messages from
localhost only.

@node dot.biffrc
@subsection A per-user configuration file.

By default, when a notification arrives, @command{comsatd} prints subject,
from headers and the first five lines from the new message to the user's
tty. The user is allowed to change this behavior by using his own
configuration file. This file should be located in the user's home
directory and should be named @file{.biffrc}. It must be owned by the
user and have its permissions bits set to 0600. (@emph{Please note},
that the use of per-user configuration files may be disabled, by
specifying @samp{allow-biffrc no} in the main configuration file, see
@pxref{Configuring comsatd}).

The @file{.biffrc} file consists of a series of statements. Each
statement occupies one line and defines an action to be taken upon
arrival of a new mail. Very long lines may be split using @samp{\} as
the last character on the line. As usual, comments may be introduced with
@samp{#} character.

The actions specified in @file{.biffrc} file are executed in turn.
The following actions are defined:

@table @asis
@item beep
Produce an audible signal.
@item echo @var{string}
Output @var{string} to user's terminal device.
@item exec @var{prog} @var{arglist}
Execute program @var{prog} with arguments from @var{arglist}. @var{prog}
must be specified with absolute pathname. It may not be a setuid or
setgid program.
@end table

In the description above, @var{string} denotes any sequence of
characters. This sequence must be enclosed in a pair of double-quotes,
if it contains whitespace characters. The @samp{\} character inside a
string starts a C escape sequence. Following meta-characters may be
used in strings:

@table @asis
@item $u
Expands to username
@item $h
Expands to hostname
@item $H@{name@}
Expands to value of message header @samp{name}.
@item $B(@var{c},@var{l})
Expands to message body. @var{c} and @var{l} give maximum number of
characters and lines in the expansion. When omitted, they default to 400, 5.
@end table

@subsubsection Example I.

Dump to the user's terminal the contents of @samp{From} and
@samp{Subject} headers followed by at most 5 lines of message body.
@example
@group
echo "Mail to \a$u@@$h\a\n---\n\
From: $H@{from@}\n\
Subject: $H@{Subject@}\n\
---\n\
$B(,5)\
---\n"
@end group
@end example

@subsubsection Example II.

Produce a bell, then pop up the xmessage window on display :0.0 with
the text formatted in the same manner as in the previous example.

@example
@group
beep
exec /usr/X11R6/bin/xmessage \
-display :0.0 -timeout 10 "Mail to $u@@$h \n---\n\
From: $H@{from@}\n\
Subject: $H@{Subject@}\n\
---\n\
$B(,5)\
---\n"
@end group
@end example