emacs/doc/misc/smtpmail.texi

\input texinfo  @c -*-texinfo-*-
@setfilename ../../info/smtpmail
@settitle Emacs SMTP Library
@syncodeindex vr fn
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Copyright @copyright{} 2003-2012
Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover texts being ``A GNU Manual'',
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''.

(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.''
@end quotation
@end copying

@dircategory Emacs lisp libraries
@direntry
* SMTP: (smtpmail).             Emacs library for sending mail via SMTP.
@end direntry

@titlepage
@title{Emacs SMTP Library}
@subtitle{An Emacs package for sending mail via SMTP}
@author{Simon Josefsson, Alex Schroeder}
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top Emacs SMTP Library

@insertcopying
@end ifnottex

@menu
* How Mail Works::      Brief introduction to mail concepts.
* Emacs Speaks SMTP::   How to use the SMTP library in Emacs.
* Authentication::      Authenticating yourself to the server.
* Queued delivery::     Sending mail without an internet connection.
* Server workarounds::  Mail servers with special requirements.
* Debugging::           Tracking down problems.
* GNU Free Documentation License:: The license for this documentation.

Indices

* Index::               Index over variables and functions.
@end menu

@node How Mail Works
@chapter How Mail Works

@cindex SMTP
@cindex MTA
   On the internet, mail is sent from mail host to mail host using the
simple mail transfer protocol (SMTP).  To send and receive mail, you
must get it from and send it to a mail host.  Every mail host runs a
mail transfer agent (MTA) such as Exim that accepts mails and passes
them on.  The communication between a mail host and other clients does
not necessarily involve SMTP, however.  Here is short overview of what
is involved.

@cindex MUA
   The mail program --- also called a mail user agent (MUA) ---
usually sends outgoing mail to a mail host.  When your computer is
permanently connected to the internet, it might even be a mail host
itself.  In this case, the MUA will pipe mail to the
@file{/usr/lib/sendmail} application.  It will take care of your mail
and pass it on to the next mail host.

@cindex ISP
   When you are only connected to the internet from time to time, your
internet service provider (ISP) has probably told you which mail host
to use.  You must configure your MUA to use that mail host.  Since you
are reading this manual, you probably want to configure Emacs to use
SMTP to send mail to that mail host.  More on that in the next
section.

@cindex MDA
   Things are different when reading mail.  The mail host responsible
for your mail keeps it in a file somewhere.  The messages get into the
file by way of a mail delivery agent (MDA) such as procmail.  These
delivery agents often allow you to filter and munge your mails before
you get to see it.  When your computer is that mail host, this file is
called a spool, and sometimes located in the directory
@file{/var/spool/mail/}.  All your MUA has to do is read mail from the
spool, then.

@cindex POP3
@cindex IMAP
   When your computer is not always connected to the internet, you
must get the mail from the remote mail host using a protocol such as
POP3 or IMAP.  POP3 essentially downloads all your mail from the mail
host to your computer.  The mail is stored in some file on your
computer, and again, all your MUA has to do is read mail from the
spool.

   When you read mail from various machines, downloading mail from the
mail host to your current machine is not convenient.  In that case,
you will probably want to use the IMAP protocol.  Your mail is kept on
the mail host, and you can read it while you are connected via IMAP to
the mail host.

@cindex Webmail
   So how does reading mail via the web work, you ask.  In that case,
the web interface just allows you to remote-control a MUA on the web
host.  Whether the web host is also a mail host, and how all the
pieces interact is completely irrelevant.  You usually cannot use
Emacs to read mail via the web, unless you use software that parses
the ever-changing HTML of the web interface.

@node Emacs Speaks SMTP
@chapter Emacs Speaks SMTP

   Emacs includes a package for sending your mail to a SMTP server and
have it take care of delivering it to the final destination, rather
than letting the MTA on your local system take care of it.  This can
be useful if you don't have a MTA set up on your host, or if your
machine is often disconnected from the internet.

  Sending mail via SMTP requires configuring your mail user agent
(@pxref{Mail Methods,,,emacs}) to use the SMTP library.  How to do
this should be described for each mail user agent; for the default
mail user agent the variable @code{send-mail-function} (@pxref{Mail
Sending,,,emacs}) is used; for the Message and Gnus user agents the
variable @code{message-send-mail-function} (@pxref{Mail
Variables,,,message}) is used.

@example
;; If you use the default mail user agent.
(setq send-mail-function 'smtpmail-send-it)
;; If you use Message or Gnus.
(setq message-send-mail-function 'smtpmail-send-it)
@end example

  Before using SMTP you must find out the hostname of the SMTP server
to use.  Your system administrator should provide you with this
information, but often it is the same as the server you receive mail
from.

@table @code
@item smtpmail-smtp-server
@vindex smtpmail-smtp-server
@vindex SMTPSERVER
  The variable @code{smtpmail-smtp-server} controls the hostname of
the server to use.  It is a string with an IP address or hostname.  It
defaults to the contents of the @env{SMTPSERVER} environment
variable, or, if empty, the contents of
@code{smtpmail-default-smtp-server}.

@item smtpmail-default-smtp-server
@vindex smtpmail-default-smtp-server
  The variable @code{smtpmail-default-smtp-server} controls the
default hostname of the server to use.  It is a string with an IP
address or hostname.  It must be set before the SMTP library is
loaded.  It has no effect if set after the SMTP library has been
loaded, or if @code{smtpmail-smtp-server} is defined.  It is usually
set by system administrators in a site wide initialization file.
@end table

The following example illustrates what you could put in
@file{~/.emacs} to set the SMTP server name.

@example
;; Send mail using SMTP via mail.example.org.
(setq smtpmail-smtp-server "mail.example.org")
@end example

@cindex Mail Submission
SMTP is normally used on the registered ``smtp'' TCP service port 25.
Some environments use SMTP in ``Mail Submission'' mode, which uses
port 587.  Using other ports is not uncommon, either for security by
obscurity purposes, port forwarding, or otherwise.

@table @code
@item smtpmail-smtp-service
@vindex smtpmail-smtp-service
  The variable @code{smtpmail-smtp-service} controls the port on the
server to contact.  It is either a string, in which case it will be
translated into an integer using system calls, or an integer.
@end table

The following example illustrates what you could put in
@file{~/.emacs} to set the SMTP service port.

@example
;; Send mail using SMTP on the mail submission port 587.
(setq smtpmail-smtp-service 587)
@end example

@node Authentication
@chapter Authentication

@cindex SASL
@cindex CRAM-MD5
@cindex LOGIN
@cindex STARTTLS
@cindex TLS
@cindex SSL
Many environments require SMTP clients to authenticate themselves
before they are allowed to route mail via a server.  The two following
variables contains the authentication information needed for this.

The first variable, @code{smtpmail-auth-credentials}, instructs the
SMTP library to use a SASL authentication step, currently only the
CRAM-MD5 and LOGIN mechanisms are supported and will be selected in
that order if the server support both.

The second variable, @code{smtpmail-starttls-credentials}, instructs
the SMTP library to connect to the server using STARTTLS.  This means
the protocol exchange may be integrity protected and confidential by
using the Transport Layer Security (TLS) protocol, and optionally also
authentication of the client and server.

TLS is a security protocol that is also known as SSL, although
strictly speaking, SSL is an older variant of TLS.  TLS is backwards
compatible with SSL.  In most mundane situations, the two terms are
equivalent.

The TLS feature uses the elisp package @file{starttls.el} (see it for
more information on customization), which in turn require that at
least one of the following external tools are installed:

@enumerate
@item
The GnuTLS command line tool @samp{gnutls-cli}, you can get it from
@url{http://www.gnu.org/software/gnutls/}.  This is the recommended
tool, mainly because it can verify the server certificates.

@item
The @samp{starttls} external program, you can get it from
@file{starttls-*.tar.gz} from @uref{ftp://ftp.opaopa.org/pub/elisp/}.
@end enumerate

It is not uncommon to use both these mechanisms, e.g., to use STARTTLS
to achieve integrity and confidentiality and then use SASL for client
authentication.

@table @code
@item smtpmail-auth-credentials
@vindex smtpmail-auth-credentials
  The variable @code{smtpmail-auth-credentials} contains a list of
hostname, port, username and password tuples.  When the SMTP library
connects to a host on a certain port, this variable is searched to
find a matching entry for that hostname and port.  If an entry is
found, the authentication process is invoked and the credentials are
used.

The hostname field follows the same format as
@code{smtpmail-smtp-server} (i.e., a string) and the port field the
same format as @code{smtpmail-smtp-service} (i.e., a string or an
integer).  The username and password fields, which either can be
@code{nil} to indicate that the user is prompted for the value
interactively, should be strings with the username and password,
respectively, information that is normally provided by system
administrators.

@item smtpmail-starttls-credentials
@vindex smtpmail-starttls-credentials
  The variable @code{smtpmail-starttls-credentials} contains a list of
tuples with hostname, port, name of file containing client key, and
name of file containing client certificate.  The processing is similar
to the previous variable.  The client key and certificate may be
@code{nil} if you do not wish to use client authentication.
@end table

The following example illustrates what you could put in
@file{~/.emacs} to enable both SASL authentication and STARTTLS.  The
server name (@code{smtpmail-smtp-server}) is @var{hostname}, the
server port (@code{smtpmail-smtp-service}) is @var{port}, and the
username and password are @var{username} and @var{password}
respectively.

@example
;; Authenticate using this username and password against my server.
(setq smtpmail-auth-credentials
      '(("@var{hostname}" "@var{port}" "@var{username}" "@var{password}")))

;; Note that if @var{port} is an integer, you must not quote it as a
;; string.  Normally @var{port} should be the integer 25, and the example
;; become:
(setq smtpmail-auth-credentials
      '(("@var{hostname}" 25 "@var{username}" "@var{password}")))

;; Use STARTTLS without authentication against the server.
(setq smtpmail-starttls-credentials
      '(("@var{hostname}" "@var{port}" nil nil)))
@end example

@node Queued delivery
@chapter Queued delivery

@cindex Dialup connection
If you connect to the internet via a dialup connection, or for some
other reason don't have permanent internet connection, sending mail
will fail when you are not connected.  The SMTP library implements
queued delivery, and the following variable control its behavior.

@table @code
@item smtpmail-queue-mail
@vindex smtpmail-queue-mail
  The variable @code{smtpmail-queue-mail} controls whether a simple
off line mail sender is active.  This variable is a boolean, and
defaults to @code{nil} (disabled).  If this is non-@code{nil}, mail is
not sent immediately but rather queued in the directory
@code{smtpmail-queue-dir} and can be later sent manually by invoking
@code{smtpmail-send-queued-mail} (typically when you connect to the
internet).

@item smtpmail-queue-dir
@vindex smtpmail-queue-dir
  The variable @code{smtpmail-queue-dir} specifies the name of the
directory to hold queued messages.  It defaults to
@file{~/Mail/queued-mail/}.
@end table

@findex smtpmail-send-queued-mail
  The function @code{smtpmail-send-queued-mail} can be used to send
any queued mail when @code{smtpmail-queue-mail} is enabled.  It is
typically invoked interactively with @kbd{M-x
smtpmail-send-queued-mail RET} when you are connected to the internet.

@node Server workarounds
@chapter Server workarounds

Some SMTP servers have special requirements.  The following variables
implement support for common requirements.

@table @code

@item smtpmail-local-domain
@vindex smtpmail-local-domain
  The variable @code{smtpmail-local-domain} controls the hostname sent
in the first @code{EHLO} or @code{HELO} command sent to the server.
It should only be set if the @code{system-name} function returns a
name that isn't accepted by the server.  Do not set this variable
unless your server complains.

@item smtpmail-sendto-domain
@vindex smtpmail-sendto-domain
  The variable @code{smtpmail-sendto-domain} makes the SMTP library
add @samp{@@} and the specified value to recipients specified in the
message when they are sent using the @code{RCPT TO} command.  Some
configurations of sendmail requires this behavior.  Don't bother to
set this unless you have get an error like:

@example
        Sending failed; SMTP protocol error
@end example

when sending mail, and the debug buffer (@pxref{Debugging})) contains
an error such as:

@example
        RCPT TO: @var{someone}
        501 @var{someone}: recipient address must contain a domain
@end example

@end table


@node Debugging
@chapter Debugging

Sometimes delivery fails, often with the generic error message
@samp{Sending failed; SMTP protocol error}.  Enabling one or both of
the following variables and inspecting a trace buffer will often give
clues to the reason for the error.

@table @code

@item smtpmail-debug-info
@vindex smtpmail-debug-info
  The variable @code{smtpmail-debug-info} controls whether to print
the SMTP protocol exchange in the minibuffer, and retain the entire
exchange in a buffer @samp{*trace of SMTP session to @var{server}*},
where @var{server} is the name of the mail server to which you send
mail.

@item smtpmail-debug-verb
@vindex smtpmail-debug-verb
  The variable @code{smtpmail-debug-verb} controls whether to send the
@code{VERB} token to the server.  The @code{VERB} server instructs the
server to be more verbose, and often also to attempt final delivery
while your SMTP session is still running.  It is usually only useful
together with @code{smtpmail-debug-info}.  Note that this may cause
mail delivery to take considerable time if the final destination
cannot accept mail.

@end table

@node GNU Free Documentation License
@chapter GNU Free Documentation License
@include doclicense.texi

@node Index
@chapter Index

@section Concept Index

@printindex cp

@section Function and Variable Index

@printindex fn

@bye