@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
* imap4d::      IMAP4 daemon.
* pop3d::       POP3 daemon.
* frm::         List headers from a mailbox.
* mail::        Send and receive mail.
* messages::    Count the number of messages in a mailbox.
* readmsg::     Extract messages from a folder.
* sieve::       Filter a mailbox.
* guimb::       Mailbox scanning and processing language.
* comsatd::     Comsat daemon.
@end menu

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

imap4d has two operation modes:

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

@example
imap4  stream tcp nowait  root  /usr/local/sbin/imap4d imap4d
@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 @samp{-d} command line switch.
@end table

@subheading Command line options

@table @samp
@item -d[NUMBER]
@itemx --daemon[=NUMBER]
Run in standalone mode. An optional 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
@samp{-d} and its parameter.
@item -h
@itemx --help
Display short help message and exit.
@item -i
@itemx --inetd
Run in inetd mode. 
@item -p NUMBER
@itemx --port NUMBER
Listen on given port NUMBER. This option is meaningful only in
standalone mode. It defaults to port 143.
@item -t NUMBER
@itemx --timeout NUMBER
Set idle timeout to given 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 @file{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 @samp{-d} command line switch.
@end table

@subheading Command line options

@table @samp
@item -d[NUMBER]
@itemx --daemon[=NUMBER]
Run in standalone mode. An optional 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
@samp{-d} and its parameter.
@item -h
@itemx --help
Display short help message and exit.
@item -i
@itemx --inetd
Run in inetd mode. 
@item -p NUMBER
@itemx --port NUMBER
Listen on given port NUMBER. This option is meaningful only in
standalone mode. It defaults to port 110.
@item -t NUMBER
@itemx --timeout NUMBER
Set idle timeout to given 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 @file{frm} command outputs a header information of
the selected messages in a mailbox. By default, @file{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 following command line options alter the behavior of the program:

@table @samp
@item -h
@itemx --help
Display short help message and exit.
@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 @samp{-s} options are allowed.
@item -t
@itemx --align
Tidy mode. Currently is not implemented. Included for compatibility with
@file{frm} program from Elm package.
@item -v
@itemx --version
Display version information and exit
@end table

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

@code{Mail} is an enhanced version of standard @file{/bin/mail} program.
As well as its predecessor, it can be used either in sending mode or
in reading mode. @code{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, @code{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 @samp{--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 @file{mail} program is:

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

@file{Mail} understands following command line options:

@table @samp
@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 (@samp{-f}), and its parameter. Similarly,
when using long option (@samp{--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 -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. @file{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.

@emph{Please note}, that both commands allow you to edit the body of the
message, and not its headers. To change message headers, see
@ref{Modifying the Headers}.

@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
@file{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, @file{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 @file{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 @samp{--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, @file{mail} displays the first page of header
lines and enters interactive mode. In interactive mode, @file{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 @file{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, @file{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}. If the variable @code{crt}
is set and the number of lines in the message is greater than the number
of lines on screen, the message is piped through pager command specified
by environment variable @code{PAGER}. 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 Conditional statements

The conditional statement allows to execute a set of mail commands
depending on the mode the @file{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 @file{mail} is operating in mail sending mode.
@item r
True if @file{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 @file{mail} command prompt if the variable
@code{autoinc} is set.

@node Shell Escapes
@subsubsection Shell escapes

To run arbitrary shell command from @file{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 @file{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.
@*Default: True in interactive mode, False otherwise.

If @code{True}, any messages with number of lines greater than number of
lines on terminal screen (as determined by @code{screen} variable) will
be printed using program set in the environment variable @code{ENVIRON}.

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

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

@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 @samp{--nosum} (@samp{-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}, @file{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 @samp{--quit} (@samp{-q}) option.

When set, causes keyboard interrupts to terminate the program.

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

When this variable is set, @file{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, @file{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
@file{mail} command.

When run with @samp{--norc} (@samp{-N}) option, @file{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 @samp{--with-mail-rc} option. It defaults to
@file{@var{sysconfdir}/mail.rc}.

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

@code{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 accepts following command line options:

@table @samp
@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 is currently in development

@page
@node sieve
@section sieve
@pindex sieve

The program is currently in development

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

@file{Guimb} is for mailboxes what @file{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.

@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
@file{guimb} via the following options:

@table @samp
@item -e
@itemx --expression EXPR
Execute scheme expression.
@item -f
@itemx --file PROGFILE
Read and execute program from PROGFILE.
@end table

You can specify both of them. In this case, the PROGFILE is executed
first.

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

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

@table @code
@item guimb [OPTIONS] [mailbox...]
The resulting mailbox is not saved, unless the user-supplied
scheme program saves it.
@item guimb [OPTIONS] --mailbox DEFMBOX
The contents of DEFMBOX is processed and is replaced with the resulting
mailbox contents. Useful for applying filters to user's mailbox.
@item guimb [OPTIONS] --mailbox DEFMBOX mailbox [mailbox...]
The contents of specified mailboxes is processed, and the resulting
mailbox contents is appended to DEFMBOX.
@item guimb [OPTIONS] --user USER [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 @file{guimb} as a mail delivery agent.
@end table

If no mailboxes are specified in the command line, @file{guimb} reads
and processes its standard input.

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

Sometimes it is necessary to pass some command line options to the
scheme procedure. This can be done via @samp{-g}
(@samp{--guile-command}) command line option. For example:

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

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

@example
progfile -opt 24
@end example

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

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

All arguments enclosed between @samp{-@{} and @samp{-@}} are not processed
by @file{guimb}, they are instead passed to the Scheme program verbatim.

@node Guimb Invocation Summary
@subsection Guimb Invocation Summary

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

@table @samp
@item -d
@itemx --debug
Start with debugging evaluator and backtraces.
@item -e EXPR
@itemx --expression EXPR
Execute given Scheme expression.
@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 @samp{-@{} and @samp{-@}}
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

@table @samp
@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 -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 @samp{-c} or @samp{--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 @file{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 @file{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, @file{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 @file{comsatd} receive the notification messages from
localhost only.

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

By default, when a notification arrives, @file{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