LDP/LDP/howto/linuxdoc/Mail-User-HOWTO.sgml

<!doctype linuxdoc system>
<article>
<title>The Linux Mail User HOWTO
<author>Eric S. Raymond, <tt>&lt;esr@thyrsus.com&gt;</tt>
<date>v2.2, 07 May 1999

<abstract>
This document is an introduction to the world of <idx>electronic
mail</idx> (<idx>email</idx>) under Linux. It focuses on user-level
issues and typical configurations for Linux home and small-business
machines connected to the net via an ISP.

You need to read this if you plan to communicate locally or to remote
sites via electronic mail.  You probably do <em>not</em> need to read
this document if don't exchange electronic mail with other users on
your system or with other sites.

For information on configuring and administering mail, see the
Mail Administrator HOWTO.
</abstract>

<toc>

<sect>Introduction
<p>
The intent of this document is to explain how email works, and answer
some of the questions that appear to meet the definition of
`frequently asked questions' about e-mail software under Linux.

Modern Linux distributions give you a usable, preconfigured setup for
electronic mail out of the box, usually featuring a late version of
<idx>sendmail-v8</idx>.  This HOWTO will assume that you have such a
setup and a working Internet connection.

(For information on how to set up a PPP or SLIP link to an ISP, see
the <url url="http://metalab.unc.edu/LDP/HOWTO/ISP-Hookup-HOWTO.html"
name="ISP Hookup HOWTO">.)

Accordingly, unlike Vince Skahan's 1.x versions, this HOWTO focuses on
user issues and architecture; most technical hair about UUCP, IDA
sendmail and other formerly important topics has been dropped.

<sect1>New versions of this document
<p>
This document will be posted monthly to the newsgroup <url
url="news:comp.os.linux.answers" name="comp.os.linux.answers"> You
should also be able to view the latest version of this HOWTO on the
World Wide Web at <url
url="http://metalab.unc.edu/LDP/HOWTO/Mail-User-HOWTO.html">.

<sect1>Hardware requirements for email programs
<p>
There are no specific hardware requirements for mail under Linux.
If you have the hardware necessary to connect to the Internet, it
can support email over that link.

<sect1>Software sources for email programs
<p>
The software you will need for email support is probably preinstalled
in your Linux distribution.  You will find updates on the
<url url="http://metalab.unc.edu/pub/Linux" name="Metalab Linux
Archive">, especially in the <url
url="http://metalab.unc.edu/pub/Linux/system/mail" 
name="mail subdirectory">.

<sect>Mail User Agents
<p>
This section contains information related to user agents, which means
the software the user sees and uses.  This software relies on the
transport agents described in the Mail Administrator's HOWTO (which
also include user=agent configuration and troubleshooting tips for
administrators).

<sect1>Setting your mail editor<label id="emacsclient">
<p>
Mail user agents call out to some editor to assist composition of
mail.  Which editor is the default varies.  Most of them respect 
a convention going back to Unix's early days; the contents of the
environment variable VISUAL, if it exists, is taken as the name
of your preferred editor.  If VISUAL is not set, the variable 
EDITOR is checked.

Popular values for EDITOR include `vi' and `emacs'.  But if you are,
like me, the sort who always has an Emacs running, the most useful way
to set EDITOR is to the value `emacsclient'.  Use this with the
following lines in your .emacs file:

<code>
(autoload 'server-edit "server" nil t)
(server-edit)
</code>

The emacsclient program, when it runs, tries to establish
communication with an Emacs instance you already have running and
hand the mail message temporary file to that Emacs to be edited.
The effect of this will be that when your mailer calls out for an
editor, a mail composition window pops open inside your Emacs.

When you are ready to hand the file back to the mailer for 
sending, type C-x #.  The mail buffer will leave your display
and the emacsclient instance your mailer called will return, handing
control back to the mailer.

It is possible to have more than one emacsclient instance open at once
without confusing Emacs.  However, calling up another Emacs while an
emacsclient session is running can confuse emacsclient enough that 
it won't be able to find either instance afterwards.  If this happens,
shut down all your Emacs instances and restart just one.

<sect1>mutt
<p>
This is what I use and recommend.  It is descended from elm and has
similar commands by default, but is much more powerful and
configurable.  It can be a POP3 or IMAP client, and includes excellent
support for MIME and PGP.  There is a Mutt home page at <url
name="http://www.mutt.org" url="http://www.mutt.org">.

Mutt respects the EDITOR/VISUAL convention.

<sect1>elm
<p>
Elm was the first modern, screen-oriented Unix mailer, but has been
stagnant for years now and is being displaced by Mutt.  Some versions
of elm have POP3 support built in. For more information, see the elm
sources and installation instructions in the <url
url="http://metalab.unc.edu/pub/Linux/system/mail" name="Metalab mail
user agents directory">.  Here are a few points that occasionally trip
people up:

No, stock elm is not PGP-aware.  There are PGP support patches, but
Mutt's PGP support is superior.  If you want to use PGP, I recommend Mutt.

Elm respects the EDITOR/VISUAL convention.

<sect1>pine
<p>
Pine is a user agent designed for novices; it includes news-reading
capability and built-in support for the IMAP remote-mail protocol.  A
lot of people swear by it for new users.  I find its impoverished
command set, limited configurability and native editor hard to take.
It has excellent built-in IMAP support, however.  If you want to check
it out, the distribution is available at <url
name="http://www.washington.edu/pine"
url="http://www.washington.edu/pine">.

Pine respects the EDITOR/VISUAL convention.

<sect1>Netscape
<p>
The Netscape browser has POP3 and IMAP remote-mail capability built
into it, so it can be used as a mail user agent.  I don't recommend
this; it doesn't specialize in being an MUA, and therefore does not
offer many of the services that real MUAs do (such as aliases and
PGP handling).  

Neetscape supplies its own mini-editor, the same one used throughout 
the browser (e.g. for text fields in forms).

<sect1>Emacs rmail/smail and vm.
<p>
Emacs has a mode called smail that can send mail, and another called
rmail that can read mail.  The smail mode can be quite useful, as you
get to compose mail inside a full Emacs environment (but see also the
discussion of <ref id="emacsclient" name="emacsclient"> elsewhere in
this document).

The rmail mode, on the other hand, is not recommended.  Every time you
run it, it converts your inbox to BABYL format; ordinary mail tools
will choke on that.  (If this happens to you, do <tt>M-x unrmail</tt>
from the Emacs command line.)

There is a mailreader for emacs called `vm' that writes and reads
standard V7 mailboxes.  It is not distributed with GNU Emacs,
but you can find its home page at <url
url="http://www.wonderworks.com/vm/"
name="http://www.wonderworks.com/vm/">.

Emacs smail/rmail/vm do not respect the EDITOR/VISUAL
convention. Instead, you use the Emacs they're embedded in.

<sect1>BSD mail
<p>
If you simply type `mail' to the shell on a Linux or any other modern
Unix, you will invoke some variant of the BSD Mail program.  It has a
line-oriented interface originally designed for use on TTYs.  It is,
at this point, only of historical interest.

BSD Mail invented the EDITOR/VISUAL convention.

<sect1>Other user agents
<p>
The following also are known to run under Linux.  Consult `archie' to
find them...
<itemize>
<item>mush      - mail user's shell, very powerful for filtering and
                  batch processing
<item>mh	- mail handler, yet another mail user agent
</itemize>

I don't know enough about mh or mush to describe them in detail.
They both have rather complex interfaces and are designed for
sophisticated mail users.

<sect>Advanced topics
<p>
<sect1>Aliases
<p>
An `alias' is a way to set up a pseudo-address that simply directs
mail to another (single) address.  There are two kinds of aliases:
MUA aliases and MTA aliases.

An MUA alias is one you set up in your MUA as a kind of personal shorthand.
Other people will not be able to see or use this alias.
For example, you could write 

<code>
alias esr	Eric S. Raymond	<esr@thyrsus.com>
</code>

in your mutt configuration file.  This would tell mutt that when it
sees `esr' in an address line, it should behave as through you had
typed `esr@thyrsus.com',  Or you can type `mutt esr' and the expanded
address will be automatically filled in on the `to' line.

An MTA alias is one your MTA expands; it will be usable by everyone,
both on your machine and remotely.  To create MTA aliases you must
modify a system file, usually but not always <file>/etc/aliases</file>
(the location depends on your MTA).  It may be instructive for you to
look at the <file>/etc/aliases</file> on your system; it should
contain a number of standard aliases such as `postmaster'.

Your MTA may also allow the target of an alias to be a filename, which
will be treated as a mailbox the mail is to be appended to (this is
useful for archiving mail).  It may also allow the target of an alias
to be a program, in which case mail to that alias will be passed to
an instance of the program on its standard input.

<sect1>Forwarding
<p>
MTA aliases usually require administrator privileges to set up.  But
it is desirable for mail users to be able to set up forwarding of
their own mail without administrator intervention.

To support this, most MTAs follow sendmail's lead and look for a file
called <tt><idx>.forward</idx></tt> in your home directory.  The
contents of this file is interpreted like the target of an alias which
should receive all your mail.  The most common use for this facility
is to redirect your mail to an account on another machine.

<sect1>Auto-answering
<p>
Another common use for the <tt>.forward</tt> facility is to pass your
mail to a `vacation' program.  A vacation program reads incoming mail
and automatically generates a canned reply to it; they are so called
because the most common form of canned reply is to inform the sender
that you are on vacation and will not be reachable until a given date.

There is no one standard vacation program that is in universal use.  
There are two good reasons for this: one, that such a program is
very easy to write as a shellscript of filter rule (see below); and
two, that vacation programs interact badly with mailing lists.

You should temporarily unsubscribe from all mailing lists you are on
before setting up auto-answering; otherwise, all members of the
mailing lists mail find they are being flooded with canned messages
by your vacation program.  This is considered very rude behavior
and will guarantee you quite a frosty reception on your return.

<sect1>Mailing lists
<p>
A mailing list is a pseudo-address that sends mail to more than
one user.

In its simplest form, mailing list is just an MTA alias with more than
one recipient. Some small mailing lists are maintained this way.
Sendmail assists by supporting a syntax in <file>/etc/aliases</file>
that includes the contents of a given mailing list file in the target
side of an alias.  It looks like this:

<code>
admin-list:     ":include:/usr/home/admin/admin-list"
</code>

with the advantage that the admin-list file can live in
unprivileged-user space somewhere (root is only needed to set
up the original inclusion). Some other MTAs have similar features.

These simple lists are commonly called `<idx>mail reflectors</idx>'.
There are a couple of problems with mail reflectors.  One is that
bounce messages from failed attempts to broadcast goes to all users.
Another is that all subscriptions and unsubscriptions have to be done
manually by the mailing list administrator.

A kind of software called a <idx>mailing list manager</idx> has
evolved to address these problems and other related ones.  Its
most important function is to permit mailing list users to subscribe
and unscubscribe without going through the list maintainer.

A mailing-list manager keeps its own user-list information and hooks up
to the MTA through a program alias in <file>/etc/aliases</file>.
For example, if the admin-list above were going through the mailing
list manager called SmartList on a sendmail system, a portion of
<file>/etc/aliases</file> might look like this:

<code>
admin-list: "|/usr/home/smartlist/bin/flist admin-list"
admin-list-request: "|/usr/home/smartlist/bin/flist admin-list-request"
</code>

Note that this is a pair of aliases.  It is conventional for real
mailing lists to have a <idx>request address</idx> to be used for user
subscription and unsubscription requests.  It is considered rude and
ignorant to send subscription/unsubscription requests to the main
address of such a list -- don't do it.

The robot sitting behind the request address may offer other features
besides just subscription/unsubscription.  It may respond to help
requests, allow you to query who is on the list, or give you automated
access to list archives.  It may also allow list administrators to
restrict posting to known members, set the list to auto-subscribe
nonmembers when they first post, or set various security policy
options.  Mailing-list managers differ primarily in the design and
range of these secondary features.

Unfortunately, the format for sending commands to mailing-list request
robots is not standard.  Some expect commands in the subject line, 
some ignore the subject line and expect commands in the message body.
You need to pay attention to the response mail you get when you first
subscribe; it's a good idea to save such mail to a subscriptions
mailbox for later reference.

The most important mailing-list managers to know about are majordomo,
listserv, listproc, and smartlist; majordomo is the most popular by a
considerable margin.  There is a rather comprehensive <url name="list"
url="http://www.catalog.com/vivian/mailing-list-software.html"> of
such packages on the Web.

For more about mailing list managers, consult the resources at the
<url name="List-Managers Mailing List"
url="http://www.greatcircle.com/list-managers/">, including the FAQ
(note: this list is <em>not</em> appropriate for how-to questions).  

<sect1>Mail filters
<p>
A <idx>mail filter</idx> is a program that sits between your local
delivery agent and you, automatically dispatching or rejecting 
mail before you see it.

Mail filters have a number of uses.  The most important are spam
filtering, dispatching to multiple mailboxes by topic or sender,
and auto-answering mail.

Typically, you set up mail filtering by putting a program alias 
for the filter program in your .forward file, and writing a 
file of filtering rules.  The format and location of the filter
rules file varies between filter programs.

There are good feature summaries of the three major mail filters
(procmail, mailagent, and deliver) in <url name="part 3"
url="http://www.faqs.org/faqs/mail/setup/unix/part3/index.html"> of
Chris Lewis's Email Software Survey.  The most popular of these
is (despite its rather nasty rule syntax) procmail, which is 
universally present on Linux systems (and, indeed, is generally used
as the system's local delivery agent).

<sect1>Coping with spam
<p>
Spam is sometimes known as `UCE' (Unsolicited Commercial Email) or
`UBE' (Unsolicited Bulk Email).  As these names imply, it is an
obnoxious form of advertising that stuffs your mailbox with form
letters.  (The term `spam' comes from a Monty Python's Flying Circus
skit in which a choir of Vikings endlessly repeats the chant
"Spam spam spam spam...").
<p>
Most spam seems to consist of solicitations for pyramid schemes, ads
for pornography, or (annoyingly) attempts to sell spam-sending
programs.  A few individual spams (like MAKE MONEY FAST or the Craig
Shergold postcard hoax) have been so persistent as to become
legendary.  Spam tends to be both verbose and illiterate.  It's a
waste of time and a huge waste of network bandwidth.
<p>
The spam epidemic seems to have peaked in mid-1997 and been slowly
in decline since, but it can still be a serious annoyance.  If you're
being deluged with spam, get educated.  Browse the <url
url="http://spam.abuse.net/" name="Fight Spam on the Internet!"> page.
The <url url="http://www.mindworkshop.com/alchemy/nospam.html"
name="Death To Spam!"> page is particularly effective on methods  for
stopping or backtracking spam.

<sect>Other sources of information
<p>   
<sect1>USENET
<p>
There are a number of Usenet groups devoted to electronic-mail
technical issues:

<itemize>
<item><htmlurl url="news:comp.mail.elm" name="comp.mail.elm">
	the ELM mail system.
<item><htmlurl url="news:comp.mail.mh" name="comp.mail.mh">
	The Rand Message Handling system.
<item><htmlurl url="news:comp.mail.mime" name="comp.mail.mime">
	Multipurpose Internet Mail Extensions.
<item><htmlurl url="news:comp.mail.misc" name="comp.mail.misc">
	General discussions about computer mail.
<item><htmlurl url="news:comp.mail.multi-media" name="comp.mail.multi-media">
	Multimedia Mail.
<item><htmlurl url="news:comp.mail.mush" name="comp.mail.mush">
	The Mail User's Shell (MUSH).
<item><htmlurl url="news:comp.mail.sendmail" name="comp.mail.sendmail">
	the BSD sendmail agent.
<item><htmlurl url="news:comp.mail.smail" name="comp.mail.smail">
	the smail mail agent.
<item><htmlurl url="news:comp.mail.uucp" name="comp.mail.uucp">
	Mail in the uucp environment.
</itemize>

<sect1>Books
<p>   
The following is a non-inclusive set of books that will help...

<itemize>
<item>``<em>Sendmail</em>" from O'Reilly and Associates is
the definitive reference on sendmail-v8 and sendmail+IDA.  It's a
``must have'' for anybody hoping to make sense out of sendmail without
bleeding in the process.

<item>"<em>The Internet Complete Reference</em>" from Osborne is a
fine reference book that explains the various services available on
Internet and is a great source for information on news, mail, and
various other Internet resources.

<item>"<em>The Linux Networking Administrators' Guide</em>" from Olaf
Kirch of the LDP is available on the net and is also
published by (at least) O'Reilly and SSC.  It makes a fine
one-stop shopping guide to learn about everything you ever imagined
you'd need to know about Unix networking.
</itemize>

<sect1>Periodic USENET Postings
<p>
Also worth mentioning, is Chris Lewis' periodic posting on unix e-mail
software, which is available on 
<url url="ftp://rtfm.mit.edu/pub/usenet/comp.mail.misc">
as the files named ``UNIX_Email_Software_Survey_*''.  An HTMLized
version is at <url url="http://www.faqs.org/faqs/mail/setup/unix/"
name="http://www.faqs.org/faqs/mail/setup/unix/">.  At time writing in
1999 this posting has not been seriously updated since 1996, however.

<sect1>Where <em>NOT</em> to look for help
<p>
There is no longer anything special about configuring and running mail
under Linux, relative to other Unixes.  Accordingly, you almost
certainly do <em>NOT</em> want to be posting generic mail-related
questions to the comp.os.linux.* newsgroups.

Unless your posting is truly Linux-specific (ie, ``please tell me what routers
are already compiled into the SLS1.03 version of smail3.1.28'') you should be
asking your questions in one of the newsgroups or mailing lists referenced
above.

Let me repeat that.

There is virtually no reason to post anything mail-related in the
comp.os.linux hierarchy any more.  There are existing newsgroups in the
comp.mail.* hierarchy to handle <em>ALL</em> your questions.

<em>
If you post to comp.os.linux.* for non-Linux-specific questions, you are
looking in the wrong place for help.  The electronic mail experts hang out in
the places indicated above and generally not in the Linux groups.
</em>

<em>
Posting to the Linux hierarchy for non-linux-specific questions wastes your
time and everybody else's...and it frequently delays you from getting the
answer to your question.
</em>

<sect>Administrivia
<p>
<sect1>Feedback
<p>   
(Vince wrote this section, but my policy is the same.)
<p>
I am interested in any feedback, positive or negative, regarding the content
of this document via e-mail.  Definitely contact me if you find errors or
obvious omissions.

I read, but do not necessarily respond to, all e-mail I receive.  Requests for
enhancements will be considered and acted upon based on that day's combination
of available time, merit of the request, and daily blood pressure :-)
   
Flames will quietly go to /dev/null so don't bother.

In particular, the Linux filesystem standard for pathnames is an evolving
thing.  What's in this document is there for illustration only based on the
current standard at the time that part of the document was written and in
the paths used in the distributions or `kits' I've personally seen.  Please
consult your particular Linux distribution(s) for the paths they use.

Feedback concerning the actual format of the document should go to the HOWTO
coordinator - mail to <url url="mailto:linux-howto@metalab.unc.edu"
name="linux-howto@metalab.unc.edu">).

<sect1>Copyright Information
<p>   
The Mail-HOWTO is copyrighted (c)1999 Eric S. Raymond.  Copyright is
retained for the purpose of enforcing the Linux Documentation Project
license terms.

A verbatim copy may be reproduced or distributed in any medium physical or
electronic without permission of the author.  Translations are similarly
permitted without express permission if it includes a notice on who translated
it.
   
Short quotes may be used without prior consent by the author.  Derivative work
and partial distributions of the Mail-HOWTO must be accompanied with either a
verbatim copy of this file or a pointer to the verbatim copy.
   
Commercial redistribution is allowed and encouraged; however, the
maintainer would appreciate being notified of any such distributions
(as a courtesy).
   
In short, we wish to promote dissemination of this information through as many
channels as possible. However, we do wish to retain copyright on the HOWTO
documents.
   
We further want that <em>all</em> information provided in the HOWTOS
is disseminated.  If you have questions, please contact the Linux
HOWTO coordinator, at <tt>linux-howto@metalab.unc.edu</tt>.

<sect1>Standard Disclaimer
<p>   
Of course, we disavow any potential liability for the contents of this
document.  Use of the concepts, examples, and/or other content of this
document is entirely at your own risk.

<sect1>Acknowledgements
<p>
This was originally authored by Vince Skahan.  I have rewritten it for
the modern ISP-centric world in which UUCP is little more than a
memory.

In May 1999, the name was changed from "The Linux Electronic Mail HOWTO" to
avoid a collision with Guylhem Aznar's Mail HOWTO, which will become
the Mail Administrator HOWTO.
</article>