Configuring elmLinux Network Administrators GuidePrevChapter 17. Electronic MailNextConfiguring elmelm stands for “electronic mail” and is one
of the more reasonably named Unix tools. It provides a full-screen interface
with a good help feature. We won't discuss how to use elm
here, but only dwell on its configuration options.Theoretically, you can run elm unconfigured, and everything
works well—if you are lucky. But there are a few options that must be
set, although they are required only on occasion.When it starts, elm reads a set of configuration variables
from the elm.rc file in /etc/elm.
Then it attempts to read the file .elm/elmrc in your
home directory. You don't usually write this file yourself. It is created when
you choose “Save new options” from elm's options
menu.The set of options for the private elmrc file is also
available in the global elm.rc file. Most settings in
your private elmrc file override those of the global file.Global elm OptionsIn the global elm.rc file, you must set the options
that pertain to your host's name. For example, at the Virtual Brewery, the file
for vlager contains the following:
#
# The local hostname
hostname = vlager
#
# Domain name
hostdomain = .vbrew.com
#
# Fully qualified domain name
hostfullname = vlager.vbrew.comThese options set elm's idea of the local hostname.
Although this information is rarely used, you should set the options.
Note that these particular options only take effect when giving them in
the global configuration file; when found in your private
elmrc, they will be ignored.National Character SetsA set of standards and RFCs have been developed that amend the RFC-822
standard to support various types of messages, such as plain text,
binary data, PostScript files, etc. These standards are commonly
referred to as MIME, or Multipurpose Internet Mail Extensions. Among
other things, MIME also lets the recipient know if a character set
other than standard ASCII has been used when writing the message, for
example, using French accents or German
umlauts. elm supports these characters to some
extent.The character set used by Linux internally to represent characters is
usually referred to as ISO-8859-1, which is the name of the standard it
conforms to. It is also known as Latin-1. Any message using characters
from this character set should have the following line in its header:
Content-Type: text/plain; charset=iso-8859-1The receiving system should recognize this field and take appropriate
measures when displaying the message. The default for
text/plain messages is a
charset value of
us-ascii.To be able to display messages with character sets other than ASCII,
elm must know how to print these characters. By default,
when elm receives a message with a
charset field other than
us-ascii (or a content type other than
text/plain, for that matter), it
tries to display the message using a command called
metamail. Messages that require metamail
to be displayed are shown with an M in the very first
column in the overview screen.Since Linux's native character set is ISO-8859-1, calling
metamail is not necessary to display messages using
this character set. If elm is told that the display
understands ISO-8859-1, it will not use metamail,
but will display the message directly instead. This can be enabled by
setting the following option in the global
elm.rc:
displaycharset = iso-8859-1Note that you should set this option even when you are never going to
send or receive any messages that actually contain characters other than
ASCII. This is because people who do send such messages usually
configure their mailer to put the proper Content-Type:
field into the mail header by default, whether or not they are sending
ASCII-only messages.However, setting this option in elm.rc is not
enough. When displaying the message with its built-in pager,
elm calls a library function for each character to
determine whether it is printable. By default, this function will only
recognize ASCII characters as printable and display all other
characters as ^?. You may overcome this function by setting
the environment variable LC_CTYPE to ISO-8859-1, which tells the library to
accept Latin-1 characters as printable. Support for this and other
features have been available since Version 4.5.8 of the Linux standard library.When sending messages that contain special characters from ISO-8859-1,
you should make sure to set two more variables in the
elm.rc file:
charset = iso-8859-1
textencoding = 8bitThis makes elm report the character set as ISO-8859-1
in the mail header and send it as an 8-bit value (the default is to strip all
characters to 7-bit).Of course, all character set options we've discussed here may also be
set in the private elmrc file instead of the global one
so individual users can have their own default settings if the global one
doesn't suit them.PrevHomeNextHow Does Mail Routing Work?UpSendmail
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