The Linux Mail User HOWTO
Eric S. Raymond, <esr@thyrsus.com>
v2.2, 07 May 1999
This document is an introduction to the world of electronic mail
(email) under Linux. It focuses on user-level issues and typical con-
figurations 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 not
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.
______________________________________________________________________
Table of Contents
1. Introduction
1.1 New versions of this document
1.2 Hardware requirements for email programs
1.3 Software sources for email programs
2. Mail User Agents
2.1 Setting your mail editor
2.2 mutt
2.3 elm
2.4 pine
2.5 Netscape
2.6 Emacs rmail/smail and vm.
2.7 BSD mail
2.8 Other user agents
3. Advanced topics
3.1 Aliases
3.2 Forwarding
3.3 Auto-answering
3.4 Mailing lists
3.5 Mail filters
3.6 Coping with spam
4. Other sources of information
4.1 USENET
4.2 Books
4.3 Periodic USENET Postings
4.4 Where
5. Administrivia
5.1 Feedback
5.2 Copyright Information
5.3 Standard Disclaimer
5.4 Acknowledgements
______________________________________________________________________
1. Introduction
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
sendmail-v8. 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 ISP Hookup HOWTO <http://metalab.unc.edu/LDP/HOWTO/ISP-Hookup-
HOWTO.html>.)
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.
1.1. New versions of this document
This document will be posted monthly to the newsgroup
comp.os.linux.answers <news:comp.os.linux.answers> You should also be
able to view the latest version of this HOWTO on the World Wide Web at
<http://metalab.unc.edu/LDP/HOWTO/Mail-User-HOWTO.html>.
1.2. Hardware requirements for email programs
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.
1.3. Software sources for email programs
The software you will need for email support is probably preinstalled
in your Linux distribution. You will find updates on the Metalab
Linux Archive <http://metalab.unc.edu/pub/Linux>, especially in the
mail subdirectory <http://metalab.unc.edu/pub/Linux/system/mail>.
2. Mail User Agents
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).
2.1. Setting your mail editor
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:
______________________________________________________________________
(autoload 'server-edit "server" nil t)
(server-edit)
______________________________________________________________________
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.
2.2. mutt
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
http://www.mutt.org <http://www.mutt.org>.
Mutt respects the EDITOR/VISUAL convention.
2.3. elm
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 Metalab mail user agents
directory <http://metalab.unc.edu/pub/Linux/system/mail>. 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.
2.4. pine
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
http://www.washington.edu/pine <http://www.washington.edu/pine>.
Pine respects the EDITOR/VISUAL convention.
2.5. Netscape
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).
2.6. Emacs rmail/smail and vm.
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 ``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 M-x unrmail 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 http://www.wonderworks.com/vm/
<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.
2.7. BSD mail
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.
2.8. Other user agents
The following also are known to run under Linux. Consult `archie' to
find them...
o mush - mail user's shell, very powerful for filtering and
batch processing
o mh - mail handler, yet another mail user agent
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.
3. Advanced topics
3.1. Aliases
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
______________________________________________________________________
alias esr Eric S. Raymond <esr@thyrsus.com>
______________________________________________________________________
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 /etc/aliases (the
location depends on your MTA). It may be instructive for you to look
at the /etc/aliases 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.
3.2. Forwarding
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 .forward 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.
3.3. Auto-answering
Another common use for the .forward 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.
3.4. Mailing lists
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 /etc/aliases that includes
the contents of a given mailing list file in the target side of an
alias. It looks like this:
______________________________________________________________________
admin-list: ":include:/usr/home/admin/admin-list"
______________________________________________________________________
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 `mail reflectors'. 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 mailing list manager 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 /etc/aliases. For example,
if the admin-list above were going through the mailing list manager
called SmartList on a sendmail system, a portion of /etc/aliases might
look like this:
______________________________________________________________________
admin-list: "|/usr/home/smartlist/bin/flist admin-list"
admin-list-request: "|/usr/home/smartlist/bin/flist admin-list-request"
______________________________________________________________________
Note that this is a pair of aliases. It is conventional for real
mailing lists to have a request address 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 list
<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
List-Managers Mailing List <http://www.greatcircle.com/list-
managers/>, including the FAQ (note: this list is not appropriate for
how-to questions).
3.5. Mail filters
A mail filter 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 part 3
<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).
3.6. Coping with spam
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...").
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.
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 Fight Spam on the
Internet! <http://spam.abuse.net/> page. The Death To Spam!
<http://www.mindworkshop.com/alchemy/nospam.html> page is particularly
effective on methods for stopping or backtracking spam.
4. Other sources of information
4.1. USENET
There are a number of Usenet groups devoted to electronic-mail
technical issues:
o comp.mail.elm the ELM mail system.
o comp.mail.mh The Rand Message Handling system.
o comp.mail.mime Multipurpose Internet Mail Extensions.
o comp.mail.misc General discussions about computer mail.
o comp.mail.multi-media Multimedia Mail.
o comp.mail.mush The Mail User's Shell (MUSH).
o comp.mail.sendmail the BSD sendmail agent.
o comp.mail.smail the smail mail agent.
o comp.mail.uucp Mail in the uucp environment.
4.2. Books
The following is a non-inclusive set of books that will help...
o ``Sendmail" 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.
o "The Internet Complete Reference" 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.
o "The Linux Networking Administrators' Guide" 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.
4.3. Periodic USENET Postings
Also worth mentioning, is Chris Lewis' periodic posting on unix e-mail
software, which is available on
<ftp://rtfm.mit.edu/pub/usenet/comp.mail.misc> as the files named
``UNIX_Email_Software_Survey_*''. An HTMLized version is at
http://www.faqs.org/faqs/mail/setup/unix/
<http://www.faqs.org/faqs/mail/setup/unix/>. At time writing in 1999
this posting has not been seriously updated since 1996, however.
4.4. Where NOT to look for help
There is no longer anything special about configuring and running mail
under Linux, relative to other Unixes. Accordingly, you almost
certainly do NOT 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 ALL your questions.
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.
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.
5. Administrivia
5.1. Feedback
(Vince wrote this section, but my policy is the same.)
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 linux-howto@metalab.unc.edu <mailto:linux-
howto@metalab.unc.edu>).
5.2. Copyright Information
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 all information provided in the HOWTOS is
disseminated. If you have questions, please contact the Linux HOWTO
coordinator, at linux-howto@metalab.unc.edu.
5.3. Standard Disclaimer
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.
5.4. Acknowledgements
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.