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@setfilename mu4e.info
@settitle Mu4e @value{mu-version} user manual

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@copying
Copyright @copyright{} 2012-2016 Dirk-Jan C. Binnema

@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, no Front-Cover Texts, and no Back-Cover Texts.  A
copy of the license is included in the section entitled ``GNU Free
Documentation License.''
@end quotation
@end copying

@titlepage
@title @t{Mu4e} --- an e-mail client for GNU/Emacs
@subtitle version  @value{mu-version}
@author Dirk-Jan C. Binnema

@c The following two commands start the copyright page.
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@dircategory Emacs
@direntry
* mu4e: (Mu4e).  An email client for GNU/Emacs.
@end direntry

@contents

@ifnottex
@node Top
@top mu4e manual
@end ifnottex

@iftex
@node Welcome to mu4e
@unnumbered Welcome to mu4e
@end iftex

Welcome to @t{mu4e} @value{mu-version}.

@t{mu4e} (@t{mu}-for-emacs) is an e-mail client for GNU-Emacs version
24.4 or higher, built on top of the
@t{mu}@footnote{@url{http://www.djcbsoftware.nl/code/mu}} e-mail search
engine. @t{mu4e} is optimized for fast handling of large amounts of
e-mail.

Some of its highlights:
@itemize
@item Fully search-based: there are no folders@footnote{that is, instead of
folders, you use queries that match messages in a particular folder}, only
queries.
@item Fully documented, with example configurations
@item User-interface optimized for speed, with quick key strokes for common actions
@item Support for non-English languages (so ``angstrom''  matches ``Ångström'')
@item Asynchronous: heavy actions don't block @t{emacs}@footnote{currently,
the only exception to this is @emph{sending mail}; there are solutions
for that though --- see the @ref{FAQ}}
@item Support for cryptography --- signing, encrypting and decrypting
@item Address auto-completion based on the contacts in your messages
@item Extendable with your own snippets of elisp
@end itemize

In this manual, we go through the installation of @t{mu4e}, do some
basic configuration and explain its daily use. We also show you how you
can customize @t{mu4e} for your special needs.

At the end of the manual, there are some example configurations, to get
you up to speed quickly: @ref{Example configurations}. There's also a
section with answers to frequenly asked questions, @ref{FAQ}.

@menu
* Introduction:: Where to begin
* Getting started:: Setting things up
* Main view:: The @t{mu4e} overview
* Headers view:: Lists of message headers
* Message view:: Viewing specific messages
* Editor view:: Creating / editing messages
* Searching:: Some more background on searching/queries
* Marking:: Marking messages and performing actions
* Contexts:: Defining contexts and switching between them
* Dynamic folders:: Folders that change based on circumstances
* Actions:: Defining and using custom actions
* Extending mu4e:: Writing code for @t{mu4e}

Appendices
* Interaction with other tools:: mu4e and the rest of the world
* Example configurations:: Some examples to set you up quickly
* FAQ:: Common questions and answers
* Tips and Tricks:: Useful tips
* How it works:: Some notes about the implementation of @t{mu4e}
* Logging and debugging:: How to debug problems in @t{mu4e}
* GNU Free Documentation License::  The license of this manual
@end menu

@node Introduction
@chapter Introduction

Let's get started!

@menu
* Why another e-mail client::Aren't there enough already
* Other mail clients::Where @t{mu4e} takes its inspiration from
* What mu4e does not do::Focus on the core-business, delegate the rest
* Becoming a mu4e user::Joining the club
@end menu

@node Why another e-mail client
@section Why another e-mail client?

I (the author) spend a @emph{lot} of time dealing with e-mail, both
professionally and privately. Having an efficient e-mail client is
essential. Since none of the existing ones worked the way I wanted, I
thought about creating my own.

@command{emacs} is an integral part of my workflow, so it made a lot of
sense to use it for e-mail as well. And as I had already written an
e-mail search engine (@t{mu}), it seemed only logical to use that as a
basis.

@node Other mail clients
@section Other mail clients

Under the hood, @t{mu4e} is fully search-based, similar to programs like
@t{notmuch}@footnote{@url{http://notmuchmail.org}} and
@t{sup}@footnote{@url{http://sup.rubyforge.org/}}.

However, @t{mu4e}'s user-interface is quite different. @t{mu4e}'s mail
handling (deleting, moving etc.) is inspired by
Wanderlustu@footnote{@url{http://www.gohome.org/wl/}} (another
@t{emacs}-based e-mail client),
@t{mutt}@footnote{@url{http://www.mutt.org/}} and the @t{dired}
file-manager for emacs.

@t{mu4e} tries to keep all the `state' in your maildirs, so you can easily
switch between clients, synchronize over @abbr{IMAP}, backup with @t{rsync}
and so on. If you delete the database, you won't lose any information.

@node What mu4e does not do
@section What @t{mu4e} does not do

There are a number of things that @t{mu4e} does @b{not} do, by design:
@itemize
@item @t{mu}/@t{mu4e} do @emph{not} get your e-mail messages from
a mail server. That task is delegated to other tools, such as
@t{offlineimap}@footnote{@url{http://offlineimap.org/}},
@t{isync/mbsync}@footnote{@url{http://isync.sourceforge.net/}} or
@t{fetchmail}@footnote{@url{http://www.fetchmail.info/}}. As long as the
messages end up in a maildir, @t{mu4e} and @t{mu} are happy to deal with
them.
@item @t{mu4e} also does @emph{not} implement sending of messages; instead, it
depends on @t{smtpmail} (@inforef{Top,,smtpmail}), which is part of
@command{emacs}. In addition, @t{mu4e} piggybacks on Gnus' message editor;
@inforef{Top,,message}.
@end itemize

Thus, many of the things an e-mail client traditionally needs to do, are
delegated to other tools. This leaves @t{mu4e} to concentrate on what it does
best: quickly finding the mails you are looking for, and handle them as
efficiently as possible.

@node Becoming a mu4e user
@section Becoming a @t{mu4e} user

If @t{mu4e} sounds like something for you, give it a shot! We're trying
hard to make it as easy as possible to set up and use; and while you can
use elisp in various places to augment @t{mu4e}, a lot of knowledge
about programming or elisp shouldn't be required. The idea is to provide
sensible defaults, and allow for customization.

When you take @t{mu4e} into use, it's a good idea to subscribe to the
@t{mu}/@t{mu4e}-mailing
list@footnote{@url{http://groups.google.com/group/mu-discuss}}.

Sometimes, you might encounter some unexpected behavior while using
@t{mu4e}. It could be a bug in @t{mu4e}, it could be an issue in other
software. Or it could just be a misunderstanding. In any case, if you
want to report this (either to the mailing list or to
@url{https://github.com/djcb/mu/issues}, the latter is preferred),
please always include the following information:

@itemize
@item what did you expect that should happen? what actually happened?
@item can you provide some exact steps to reproduce?
@item what version of @t{mu4e} and @t{emacs} were you using? What operating system?
@item can you reproduce it with @command{emacs -q} and only loading @t{mu4e}?
@item if the problem is related to some specific message, please include the raw message file (appropriately anonymized, of course)
@end itemize

@node Getting started
@chapter Getting started

In this chapter, we go through the installation of @t{mu4e} and its
basic setup. After we have succeeded in @ref{Getting mail}, and
@pxref{Indexing your messages}, we discuss the @ref{Basic
configuration}.

After these steps, @t{mu4e} should be ready to go!

@menu
* Requirements:: What is needed
* Installation:: How to install @t{mu} and @t{mu4e}
* Getting mail:: Getting mail from a server
* Indexing your messages:: Creating and maintaining the index
* Basic configuration:: Settings for @t{mu4e}
* Folders::  Setting up standard folders
* Retrieval and indexing:: Doing it from @t{mu4e}
* Sending mail:: How to send mail
* Running mu4e:: Overview of the @t{mu4e} views

@end menu

@node Requirements
@section Requirements

@t{mu}/@t{mu4e} are known to work on a wide variety of Unix- and
Unix-like systems, including many Linux distributions, OS X and FreeBSD,
and even on MS-Windows (with Cygwin). @command{emacs} 23 or 24
(recommended) is required, as well as
Xapian@footnote{@url{http://xapian.org/}} and
GMime@footnote{@url{http://spruce.sourceforge.net/gmime/}}.

@t{mu} has optional support for the Guile 2.x (Scheme) programming
language. There are also some GUI-tools, which require GTK+ 3.x and
Webkit.

If you intend to compile @t{mu} yourself, you need to have the typical
development tools, such as C and C++ compilers (both @command{gcc} and
@command{clang} should work), GNU Autotools and @command{make}, and the
development packages for GMime, GLib and Xapian. Optionally (if you use them),
you also need the development packages for GTK+, Webkit and Guile.

@node Installation
@section Installation

@t{mu4e} is part of @t{mu} --- by installing the latter, the former is installed
as well. Some Linux distributions provide packaged versions of
@t{mu}/@t{mu4e}; if you can use those, there is no need to compile anything
yourself. However, if there are no packages for your distribution, if they are
outdated, or if you want to use the latest development versions, you can
follow the steps below.

First, you need make sure you have the necessary dependencies; the details
depend on your distribution. If you're using another distribution (or another
OS), the below can at least be helpful in identifying the packages to install.

We provide some instructions for Debian, Ubuntu and Fedora; if those do not
apply to you, you can follow either @ref{Building from a release tarball} or
@ref{Building from git}.

@subsection Dependencies for Debian/Ubuntu

@example
$ sudo apt-get install libgmime-2.6-dev libxapian-dev
# if libgmime-2.6-dev is not available, try libgmime-2.4-dev

# get emacs 23 or 24 if you don't have it yet
$ sudo apt-get install emacs24

# optional
$ sudo apt-get install guile-2.0-dev html2text xdg-utils

# optional: only needed for msg2pdf and mug (toy gtk+ frontend)
$ sudo apt-get install libwebkit-dev
@end example

@subsection Dependencies for Fedora

@example
$ sudo yum install gmime-devel xapian-core-devel

# get emacs 23 or 24 if you don't have it yet
$ sudo yum install emacs

# optional
$ sudo yum install html2text xdg-utils

# optional: only needed for msg2pdf and mug (toy gtk+ frontend)
$ sudo yum install webkitgtk3-devel
@end example

@subsection Building from a release tarball
@anchor{Building from a release tarball}

Using a release-tarball (as available from
GitHub@footnote{@url{https://github.com/djcb/mu/releases}}),
installation follows the typical steps:

@example
$ tar xvfz mu-<version>.tar.gz  # use the specific version
$ cd mu-<version>
# On the BSDs: use gmake instead of make
$ ./configure && make
$ sudo make install
@end example

Xapian, GMime and their dependencies must be installed.

@subsection Building from git
@anchor{Building from git}

Alternatively, if you build from the git repository or use a tarball
like the ones that @t{github} produces, the instructions are slightly
different, and require you to have @t{autotools} (@t{autoconf},
@t{autoconf-archive}, @t{automake}, @t{libtool}, and friends) installed:

@example
# get from git (alternatively, use a github tarball)
$ git clone git://github.com/djcb/mu.git

$ cd mu
$ ./autogen.sh && ./configure && make
# On the BSDs: use gmake instead of make
$ sudo make install
@end example

(Xapian, GMime and their dependencies must be installed).

After this, @t{mu} and @t{mu4e} should be installed @footnote{there's a hard
dependency between versions of @t{mu4e} and @t{mu} --- you cannot combine
different versions} on your system, and be available from the command line
in @command{emacs}.

You may need to restart @command{emacs}, so it can find @t{mu4e} in its
@code{load-path}. If, even after restarting, @command{emacs} cannot find
@t{mu4e}, you may need to add it to your @code{load-path} explicitly; check
where @t{mu4e} is installed, and add something like the following to your
configuration before trying again:
@lisp
;; the exact path may differ --- check it
(add-to-list 'load-path "/usr/local/share/emacs/site-lisp/mu4e")
@end lisp

@subsection mu4e and emacs customization

There is some support for using the @command{emacs} customization system in
@t{mu4e}, but for now, we recommend setting the values manually. Please refer
to @ref{Example configurations} for a couple of examples of this; here we go
through things step-by-step.

@node Getting mail
@section Getting mail

In order for @t{mu} (and, by extension, @t{mu4e}) to work, you need to have
your e-mail messages stored in a
@emph{maildir}@footnote{@url{http://en.wikipedia.org/wiki/Maildir}; in this
manual we use the term `maildir' for both the standard and the hierarchy of
maildirs that store your messages} --- a specific directory structure with
one-file-per-message. If you are already using a maildir, you are lucky. If
not, some setup is required:

@itemize
@item @emph{Using an external IMAP or POP server} --- if you are using an
@abbr{IMAP} or @abbr{POP} server, you can use tools like @t{getmail},
@t{fetchmail}, @t{offlineimap} or @t{isync} to download your messages into a
maildir (@file{~/Maildir}, often). Because it is such a common case, there is
a full example of setting @t{mu4e} up with @t{offlineimap} and Gmail;
@pxref{Gmail configuration}.
@item @emph{Using a local mail server} --- if you are using a local mail-server
(such as @t{postfix} or @t{qmail}), you can teach them to deliver into a
maildir as well, maybe in combination with @t{procmail}. A bit of googling
should be able to provide you with the details.
@end itemize

@node Indexing your messages
@section Indexing your messages

After you have succeeded in @ref{Getting mail}, we need to @emph{index} the
messages. That is --- we need to scan the messages in the maildir and store the
information about them in a special database. We can do that from @t{mu4e} ---
@ref{Main view}, but the first time, it is a good idea to run it from the
command line, which makes it easier to verify that everything works correctly.

Assuming that your maildir is at @file{~/Maildir}, we issue the following
command:
@example
  $ mu index --maildir=~/Maildir
@end example

This should scan your @file{~/Maildir}@footnote{In most cases, you do not even
need to provide the @t{--maildir=~/Maildir} since it is the default; see the
@t{mu-index} man-page for details} and fill the database, and give progress
information while doing so.

The indexing process may take a few minutes the first time you do it
(for thousands of e-mails); afterwards it is much faster, since @t{mu}
only scans messages that are new or have changed. Indexing is discussed
in full detail in the @t{mu-index} man-page.

After the indexing process has finished, you can quickly test if everything
worked, by trying some command-line searches, for example
@example
  $ mu find hello
@end example

which lists all messages that match @t{hello}. For more examples of searches,
see @ref{Queries}, or check the @t{mu-find} and @t{mu-easy} man pages. If all
of this worked well, we are well on our way setting things up; the next step
is to do some basic configuration for @t{mu4e}.

@node Basic configuration
@section Basic configuration

Before we can start using @t{mu4e}, we need to tell @command{emacs} to load
it. So, add to your @file{~/.emacs} (or its moral equivalent, such as
@file{~/.emacs.d/init.el}) something like:

@lisp
(require 'mu4e)
@end lisp

If @command{emacs} complains that it cannot find @t{mu4e}, check your
@code{load-path} and make sure that @t{mu4e}'s installation directory is part
of it. If not, you can add it:

@lisp
(add-to-list 'load-path MU4E-PATH)
@end lisp

with @t{MU4E-PATH} replaced with the actual path.

@node Folders
@section Folders

The next step is to tell @t{mu4e} where it can find your Maildir, and
some special folders.

So, for example@footnote{Note that the folders (@t{mu4e-sent-folder},
@t{mu4e-drafts-folder}, @t{mu4e-trash-folder} and
@t{mu4e-refile-folder}) can also be @emph{functions} that are evaluated
at runtime. This allows for dynamically changing them depending on the
situation. See @ref{Dynamic folders} for details.}:
@lisp
;; these are actually the defaults
(setq
  mu4e-maildir       "~/Maildir"   ;; top-level Maildir
  mu4e-sent-folder   "/sent"       ;; folder for sent messages
  mu4e-drafts-folder "/drafts"     ;; unfinished messages
  mu4e-trash-folder  "/trash"      ;; trashed messages
  mu4e-refile-folder "/archive")   ;; saved messages
@end lisp

Note, @code{mu4e-maildir} takes an actual filesystem-path, the other
folder names are all relative to @code{mu4e-maildir}. Also note that
this must @emph{not} be a symbolic link.

If you use @t{mu4e-context}, see @ref{Contexts and special folders} for
what that means for these special folders.

@node Retrieval and indexing
@section Retrieval and indexing with mu4e

As we have seen, we can do all of the mail retrieval @emph{outside} of
@command{emacs}/@t{mu4e}. However, you can also do it from within
@t{mu4e}.

@subsection Basics

To set up mail-retrieval from withing @t{mu4e}, set the variable
@code{mu4e-get-mail-command} to the program or shell command you want to
use for retrieving mail. You can then get your e-mail using @kbd{M-x
mu4e-update-mail-and-index}, or @kbd{C-S-u} in all @t{mu4e}-views;
alternatively, you can use @kbd{C-c C-u}, which may be more convenient
if you use emacs in a terminal.

You can kill the (foreground) update process with @kbd{q}.

It is possible to update your mail and index periodically in the
background or foreground, by setting the variable
@code{mu4e-update-interval} to the number of seconds between these
updates. If set to @code{nil}, it won't update at all. After you make
changes to @code{mu4e-update-interval}, @t{mu4e} must be restarted
before the changes take effect. By default, this will run in
background and to change it to run in foreground, set
@code{mu4e-index-update-in-background} to @code{nil}.

@subsection Handling errors during mail retrieval

If the mail-retrieval process returns with a non-zero exit code,
@t{mu4e} shows a warning (unless @code{mu4e-index-update-error-warning}
is set to @code{nil}), but then try to index your maildirs anyway
(unless @code{mu4e-index-update-error-continue} is set to @code{nil}).

Reason for these defaults is that some of the mail-retrieval programs
may return non-zero, even when the updating process succeeded; however,
it is hard to tell such pseudo-errors from real ones like `login
failed'.

If you need more refinement, it may be useful to wrap the mail-retrieval
program in a shell-script, for example @t{fetchmail} returns 1 to
indicate `no mail'; we can handle that with:
@lisp
(setq mu4e-get-mail-command "fetchmail -v || [ $? -eq 1 ]")
@end lisp
A similar approach can be used with other mail retrieval programs,
although not all of them have their exit codes documented.

@subsection Implicit mail retrieval

If you don't have a specific command for getting mail, for example
because you are running your own mail-server, you can leave
@code{mu4e-get-mail-command} at @t{"true"} (the default), in which case
@t{mu4e} won't try to get new mail, but still re-index your messages.

@subsection Speeding up indexing

If you have a large number of e-mail messages in your store,
(re)indexing might take a while. The defaults for indexing are to ensure
that we always have correct, up-to-date information about your messages,
even if other programs have modified the Maildir.

The downside of this thoroughness (which is the default) is that it is
relatively slow, something that can be noticeable with large e-mail
corpa. For a faster approach, you can use the following:

@lisp
(setq
  mu4e-index-cleanup nil      ;; don't do a full cleanup check
  mu4e-index-lazy-check t)    ;; don't consider up-to-date dirs
@end lisp

In many cases, the mentioned thoroughness might not be needed, and these
settings give a very significant speed-up. Note that you can of course
occasionally run a thorough indexing round. For further details, please
refer to the @t{mu-index} manpage.

@subsection Example setup

A simple setup could look something like:

@lisp
(setq
  mu4e-get-mail-command "offlineimap"   ;; or fetchmail, or ...
  mu4e-update-interval 300)             ;; update every 5 minutes
@end lisp

A hook @code{mu4e-update-pre-hook} is available which is run right
before starting the process. That can be useful, for example, to
influence, @code{mu4e-get-mail-command} based on the the current
situation (location, time of day, ...).

It is possible to get notifications when the indexing process does any
updates --- for example when receiving new mail. See
@code{mu4e-index-updated-hook} and some tips on its usage in the
@ref{FAQ}.

@node Sending mail
@section Sending mail

@t{mu4e} re-uses Gnus' @code{message-mode} (@inforef{Top,,message}) for
writing mail and inherits the setup for sending mail as well.

For sending mail using @abbr{SMTP}, @t{mu4e} uses @t{smtpmail}
(@inforef{Top,,smtpmail}). This package supports many different ways to
send mail; please refer to its documentation for the details.

Here, we only provide some simple examples --- for more, see @ref{Example
configurations}.

A very minimal setup:

@lisp
;; tell message-mode how to send mail
(setq message-send-mail-function 'smtpmail-send-it)
;; if our mail server lives at smtp.example.org; if you have a local
;; mail-server, simply use 'localhost' here.
(setq smtpmail-smtp-server "smtp.example.org")
@end lisp

Since @t{mu4e} (re)uses the same @t{message mode} and @t{smtpmail} that Gnus
uses, many settings for those also apply to @t{mu4e}.

@subsection Dealing with sent messages

By default, @t{mu4e} puts a copy of messages you sent in the folder determined
by @code{mu4e-sent-folder}.  In some cases, this may not be what you want -
for example, when using Gmail-over-@abbr{IMAP}, this interferes with Gmail's
handling of the sent messages folder, and you may end up with duplicate
messages.

You can use the variable @code{mu4e-sent-messages-behavior} to customize what
happens with sent messages. The default is the symbol @code{sent} which, as
mentioned, causes the message to be copied to your sent-messages folder. Other
possible values are the symbols @code{trash} (the sent message is moved to the
trash-folder (@code{mu4e-trash-folder}), and @code{delete} to simply discard
the sent message altogether (so Gmail can deal with it).

For Gmail-over-@abbr{IMAP}, you could add the following to your settings:
@verbatim
;; don't save messages to Sent Messages, Gmail/IMAP takes care of this
(setq mu4e-sent-messages-behavior 'delete)
@end verbatim
And that's it! We should now be ready to go.

For more complex needs, @code{mu4e-sent-messages-behavior} can also be
a parameter-less function that returns one of the mentioned symbols;
see the built-in documentation for the variable.

@node Running mu4e
@section Running mu4e

After following the steps in this chapter, we now (hopefully!) have a
working @t{mu4e} setup. Great! In the next chapters, we walk you
through the various views in @t{mu4e}.

For your orientation, the diagram below shows how the views relate to each
other, and the default key-bindings to navigate between them.

@cartouche
@verbatim

   [C]       +--------+   [RFCE]
   --------> | editor | <--------
  /          +--------+          \
 /         [RFCE]^                \
/                |                 \
+-------+ [sjbB]+---------+  [RET]  +---------+
| main  | <---> | headers | <---->  | message |
+-------+  [q]  +---------+ [qbBjs] +---------+
                   [sjbB]                ^
[.] | [q]
    V
  +-----+
  | raw |
  +-----+

Default bindings
----------------
R: Reply      s: search            .: raw view (toggle)
F: Forward    j: jump-to-maildir   q: quit
C: Compose    b: bookmark-search
E: Edit       B: edit bookmark-search

@end verbatim
@end cartouche

@node Main view
@chapter The main view

After you have installed @t{mu4e} (@pxref{Getting started}), you can start it
with @kbd{M-x mu4e}. @t{mu4e} does some checks to ensure everything is set up
correctly, and then shows you the @t{mu4e} main view. Its major mode is
@code{mu4e-main-mode}.

@menu
* Overview: MV Overview. What is the main view
* Basic actions::What can we do
* Bookmarks: MV Bookmarks. Jumping to other places
* Miscellaneous::Notes
@end menu

@node MV Overview
@section Overview

The main view looks something like the following:

@cartouche
@verbatim
* mu4e - mu for emacs version 0.X.X CG

  Basics

	* [j]ump to some maildir
	* enter a [s]earch query
	* [C]ompose a new message

  Bookmarks

	* [bu] Unread messages
	* [bt] Today's messages
	* [bw] Last 7 days
	* [bp] Messages with images
	* [bs] Sent mail
	* [bf] Flagged messages
	* [b]] Flow
	* [b/] Test

  Misc

	* [;]Switch context
	* [U]pdate email & database

	* [N]ews
	* [A]bout mu4e
	* [H]elp
	* [q]uit

@end verbatim
@end cartouche

In the example above, you can see the letters ``@t{CG}'', which indicate:
@itemize
@item @t{C}: support for decryption of encrypted messages, and verifying
signatures. See @ref{MSGV Crypto} in the @ref{Message view} for details.
@item @t{G}: support for the Guile 2.0 programming language
@end itemize
Whether you see both, one or none of these letters depends on the way @t{mu}
is built.

Let's walk through the menu.

@node Basic actions
@section Basic actions

First, the @emph{Basics}:
@itemize
@item @t{[j]ump to some maildir}: after pressing @key{j} (``jump''),
@t{mu4e} asks you for a maildir to visit. These are the maildirs you set in
@ref{Basic configuration} and any of your own. If you choose @key{o}
(``other'') or @key{/}, you can choose from all maildirs under
@code{mu4e-maildir}. After choosing a maildir, the messages in that maildir
are listed, in the @ref{Headers view}.
@item @t{enter a [s]earch query}: after pressing @key{s}, @t{mu4e} asks
you for a search query, and after entering one, shows the results in the
@ref{Headers view}.
@item @t{[C]ompose a new message}: after pressing @key{C}, you are dropped in
the @ref{Editor view} to write a new message.
@end itemize

@node MV Bookmarks
@section Bookmarks

The next item in the Main view is @emph{Bookmarks}. Bookmarks are predefined
queries with a descriptive name and a shortcut --- in the example above, we see
the default bookmarks. You can view the list of messages matching a certain
bookmark by pressing @key{b} followed by the bookmark's shortcut. If you'd
like to edit the bookmarked query first before invoking it, use @key{B}.

Bookmarks are stored in the variable @code{mu4e-bookmarks}; you can add your
own and/or replace the default ones; @xref{Bookmarks}.

@node Miscellaneous
@section Miscellaneous

Finally, there are some @emph{Misc} (miscellaneous) actions:
@itemize
@item @t{[U]pdate email & database} executes the shell-command in the variable
@code{mu4e-get-mail-command}, and afterwards updates the @t{mu} database;
see @ref{Indexing your messages} and @ref{Getting mail} for details.
@item @t{toggle [m]ail sending mode (direct)} toggles between sending
mail directly, and queuing it first (for example, when you are offline), and
@t{[f]lush queued mail} flushes any queued mail. This item is visible only
if you have actually set up mail-queuing. @ref{Queuing mail}
@item @t{[A]bout mu4e} provides general information about the program
@item @t{[H]elp} shows help information for this view
@item Finally, @t{[q]uit mu4e} quits your @t{mu4e}-session
@end itemize

@node Headers view
@chapter The headers view

The headers view shows the results of a query. The header-line shows
the names of the fields. Below that, there is a line with those
fields, for each matching message, followed by a footer line. The
major-mode for the headers view is @code{mu4e-headers-mode}.

@menu
* Overview: HV Overview. What is the Header View
* Keybindings::Do things with your keyboard
* Marking: HV Marking. Selecting messages for doing things
* Sorting and threading::Influencing the display
* Custom headers: HV Custom headers. Adding your own headers
* Actions: HV Actions. Defining and using actions
* Split view::Seeing both headers and messages
@end menu

@node HV Overview
@section Overview

An example headers view:
@cartouche
@verbatim
Date V       Flgs  From/To             List       Subject
06:32        Nu    To Edmund Dantès    GstDev       + Re: Gstreamer-V4L...
15:08        Nu    Abbé Busoni         GstDev         + Re: Gstreamer-V...
18:20        Nu    Pierre Morrel       GstDev           \ Re: Gstreamer...
2013-03-18   S     Jacopo              EmacsUsr   + emacs server on win...
2013-03-18   S     Mercédès            EmacsUsr     \ RE: emacs server ...
2013-03-18   S     Beachamp            EmacsUsr   + Re: Copying a whole...
22:07        Nu    Albert de Moncerf   EmacsUsr     \ Re: Copying a who...
2013-03-18   S     Gaspard Caderousse  GstDev     | Issue with GESSimpl...
2013-03-18   Ss    Baron Danglars      GuileUsr   | Guile-SDL 0.4.2 ava...
End of search results
@end verbatim
@end cartouche

Some notes to explain what you see in the example:

@itemize
@item The fields shown in the headers view can be influenced by customizing
the variable @code{mu4e-headers-fields}; see @code{mu4e-header-info} for the
list of built-in fields. Apart from the built-in fields, you can also create
custom fields using @code{mu4e-header-info-custom}; see @ref{HV Custom
headers} for details.
@item By default, the date is shown with the @t{:human-date} field, which
shows the @emph{time} for today's messages, and the @emph{date} for older
messages. If you want to distinguish between `today' and `older', you can use
the @t{:date} field instead.
@item You can customize the date and time formats with the variable
@code{mu4e-headers-date-format} and @code{mu4e-headers-time-format},
respectively. In the example, we use @code{:human-date}, which shows when the
time when the message was sent today, and the date otherwise.
@item By default, the subject is shown using the @t{:subject} field;
however, it is also possible to use @t{:thread-subject}, which shows
the subject of a thread only once, similar to the display of the
@t{mutt} e-mail client.
@item The header field used for sorting is indicated by ``@t{V}'' or
``@t{^}''@footnote{or you can use little graphical triangles; see
variable @code{mu4e-use-fancy-chars}}, corresponding to the sort order
(descending or ascending, respectively). You can influence this by a
mouse click, or @key{O}. Not all fields allow sorting.
@item Instead of showing the @t{From:} and @t{To:} fields separately, you
can use From/To (@t{:from-or-to} in @code{mu4e-headers-fields} as a more
compact way to convey the most important information: it shows @t{From:}
@emph{except} when the e-mail was sent by the user (i.e., you) --- in that case
it shows @t{To:} (prefixed by @t{To}@footnote{You can customize this by
changing the variable @code{mu4e-headers-from-or-to-prefix} (a cons cell)}, as
in the example above). To determine whether a message was sent by you,
@t{mu4e} uses the variable @code{mu4e-user-mail-address-list}, a list of
your e-mail addresses.
@item The `List' field shows the mailing-list a message is sent to;
@code{mu4e} tries to create a convenient shortcut for the mailing-list name;
the variable @code{mu4e-user-mailing-lists} can be used to add your
your own shortcuts. You can use @code{mu4e-mailing-list-patterns} to
to specify generic shortcuts, e.g. to shorten list names which contain
dots (@t{mu4e} defaults to shortening up to the first dot):
@lisp
(setq mu4e-mailing-list-patterns '(``\\([-_a-z0-9.]+\\)\.lists\.company\.com'')))
@end lisp
@item The letters in the `Flags' field correspond to the following: D=@emph{draft},
F=@emph{flagged} (i.e., `starred'), N=@emph{new}, P=@emph{passed} (i.e.,
forwarded), R=@emph{replied}, S=@emph{seen}, T=@emph{trashed},
a=@emph{has-attachment}, x=@emph{encrypted}, s=@emph{signed},
u=@emph{unread}. The tooltip for this field also contains this information.
@item The subject field also indicates the discussion threads @footnote{using
Jamie Zawinski's mail threading algorithm,
@url{http://www.jwz.org/doc/threading.html}}.
@item The headers view is @emph{automatically updated} if any changes are
found during the indexing process, and if there is no current
user-interaction. If you do not want such automatic updates, set
@code{mu4e-headers-auto-update} to @code{nil}.
@item Just before executing a search, a hook-function
@code{mu4e-headers-search-hook} is invoked, which receives the search
expression as its parameter.
@item Also, there is a hook-function @code{mu4e-headers-found-hook} available which
is invoked just after @t{mu4e} has completed showing the messages in the
headers-view.
@end itemize

@node Keybindings
@section Keybindings

Using the below key bindings, you can do various things with these messages;
these actions are also listed in the @t{Headers} menu in the @command{emacs}
menu bar.

@verbatim
key          description
===========================================================
n,p          view the next, previous message
],[          move to the next, previous unread message
y            select the message view (if it's visible)
RET          open the message at point in the message view

searching
---------
s            search
S            edit last query
/            narrow the search
b            search bookmark
B            edit bookmark before search
j            jump to maildir
M-left,\     previous query
M-right      next query

O            change sort order
P            toggle threading
Q            toggle full-search
V            toggle skip-duplicates
W            toggle include-related

marking
-------
d            mark for moving to the trash folder
=            mark for removing trash flag ('untrash')
DEL,D        mark for complete deletion
m            mark for moving to another maildir folder
r            mark for refiling
+,-          mark for flagging/unflagging
?,!          mark message as unread, read

u            unmark message at point
U            unmark *all* messages

%            mark based on a regular expression
T,t          mark whole thread, subthread

<insert>,*   mark for 'something' (decide later)
#            resolve deferred 'something' marks

x            execute actions for the marked messages

composition
-----------
R,F,C        reply/forward/compose
E            edit (only allowed for draft messages)


misc
----
;            switch context
a            execute some custom action on a header
|            pipe message through shell command
C-+,C--      increase / decrease the number of headers shown
H            get help
C-S-u        update mail & reindex
q            leave the headers buffer
@end verbatim


@node HV Marking
@section Marking

You can @emph{mark} messages for a certain action, such as deletion or
move. After one or more messages are marked, you can then execute
(@code{mu4e-mark-execute-all}, @key{x}) these actions. This two-step
mark-execute sequence is similar to what e.g. @t{dired} does. It is how
@t{mu4e} tries to be as quick as possible, while avoiding accidents.

The mark/unmark commands support the @emph{region} (i.e., ``selection'') ---
so, for example, if you select some messages and press @key{DEL}, all messages
in the region are marked for deletion.

You can mark all messages that match a certain pattern with @key{%}. In
addition, you can mark all messages in the current thread (@key{T}) or
sub-thread (@key{t}).

When you do a new search or refresh the headers buffer while you still have
marked messages, you are asked what to do with those marks --- whether to
@emph{apply} them before leaving, or @emph{ignore} them. This behavior can be
influenced with the variable @code{mu4e-headers-leave-behavior}.

For more information about marking, see @ref{Marking}.

@node Sorting and threading
@section Sorting and threading

By default, @t{mu4e} sorts messages by date, in descending order: the most
recent messages are shown at the top. In addition, the messages are
@emph{threaded}, i.e., shown in the context of a discussion thread; this also
affects the sort order.

The header field used for sorting is indicated by ``@t{V}'' or
``@t{^}''@footnote{or you can use little graphical triangles; see variable
@code{mu4e-use-fancy-chars}}, indicating the sort order (descending or
ascending, respectively).

You can change the sort order by clicking the corresponding field with the
mouse, or with @kbd{M-x mu4e-headers-change-sorting} (@key{O}); note that not
all fields can be used for sorting. You can toggle threading on/off using
@kbd{M-x mu4e-headers-toggle-threading} or @key{P}. For both of these functions,
unless you provide a prefix argument (@key{C-u}), the current search is
updated immediately using the new parameters. You can toggle full-search
(@ref{Searching}) using @kbd{M-x mu4e-headers-toggle-full-search} or @key{Q}.

If you want to change the defaults for these settings, you can use the
variables @code{mu4e-headers-sort-field} and
@code{mu4e-headers-show-threads}, as well as
@code{mu4e-headers-change-sorting} to change the sorting of the current
search results.

@node HV Custom headers
@section Custom headers

Sometimes the normal headers that @t{mu4e} offers (Date, From, To, Subject
etc.) may not be enough. For these cases, @t{mu4e} offers @emph{custom
headers} in both the headers-view and the message-view.

You can do so by adding a description of your custom header to
@code{mu4e-header-info-custom}, which is a list of custom headers.

Let's look at an example --- suppose we want to add a custom header that shows
the number of recipients for a message, i.e., the sum of the number of
recipients in the @t{To:} and @t{Cc:} fields. Let's further suppose that our function
takes a message-plist as its argument (@ref{Message functions}).

@lisp
(add-to-list 'mu4e-header-info-custom
  '(:recipnum .
     ( :name "Number of recipients"  ;; long name, as seen in the message-view
       :shortname "Recip#"           ;; short name, as seen in the headers view
       :help "Number of recipients for this message" ;; tooltip
       :function (lambda (msg)
          (format "%d"
            (+ (length (mu4e-message-field msg :to))
               (length (mu4e-message-field msg :cc))))))))
@end lisp

Or, let's get the full mailing-list name:
@lisp
(add-to-list 'mu4e-header-info-custom
 '(:full-mailing-list .
     ( :name "Mailing-list"               ;; long name, as seen in the message-view
       :shortname "ML"                    ;; short name, as seen in the headers view
       :help "Full name for mailing list" ;; tooltip
       :function (lambda (msg)
           (or (mu4e-message-field msg :mailing-list) "")))))
@end lisp

You can then add the custom header to your @code{mu4e-headers-fields},
just like the built-in headers. After evaluation, your headers-view
should include a new header @t{Recip#} with the number of recipients,
and/or @t{ML} with the full mailing-list name.

This function can be used in both the headers-view and the message-view;
if you need something specific for one of these, you can check for the
mode in your function, or create separate functions.

@node HV Actions
@section Actions

@code{mu4e-headers-action} (@key{a}) lets you pick custom actions to perform
on the message at point. You can specify these actions using the variable
@code{mu4e-headers-actions}. See @ref{Actions} for the details.

@t{mu4e} defines some default actions. One of those is for @emph{capturing} a
message: @key{a c} `captures' the current message. Next, when you're editing
some message, you can include the previously captured message as an
attachment, using @code{mu4e-compose-attach-captured-message}. See
@file{mu4e-actions.el} in the @t{mu4e} source distribution for more example
actions.

@node Split view
@section Split view

Using the @emph{Split view}, we can see the @ref{Headers view} and the
@ref{Message view} next to each other, with the message selected in the
former, visible in the latter. You can influence the way the splitting is done
by customizing the variable @code{mu4e-split-view}. Possible values are:

@itemize
@item @t{horizontal} (this is the default): display the message view below the
header view. Use @code{mu4e-headers-visible-lines} the set the number of lines
shown (default: 8).
@item @t{vertical}: display the message view on the
right side of the header view. Use @code{mu4e-headers-visible-columns} to set
the number of visible columns (default: 30).
@item @t{single-window}: single window mode. Single-window mode tries to
minimize mu4e window operations (opening, killing, resizing, etc) and buffer
changes, while still retaining the view and headers buffers. In addition, it
replaces mu4e main view with a minibuffer prompt containing the same
information.
@item anything else: don't do any splitting
@end itemize

@noindent
Some useful key bindings in the split view:
@itemize
@item @key{C-+} and @key{C--}: interactively change the number of columns or
headers shown
@item You can change the selected window from the
headers-view to the message-view and vice-versa with
@code{mu4e-select-other-view}, bound to @key{y}
@end itemize

@node Message view
@chapter The message view

After selecting a message in the @ref{Headers view}, it appears in a message
view window, which shows the message headers, followed by the message
body. Its major mode is @code{mu4e-view-mode}.

@menu
* Overview: MSGV Overview. What is the Message View
* Keybindings: MSGV Keybindings. Do things with your keyboard
* Attachments:: Opening and saving them
* Viewing images inline::Images display inside emacs
* Displaying rich-text messages::Dealing with HTML mail
* Verifying signatures and decryption: MSGV Crypto. Support for cryptography
* Custom headers: MSGV Custom headers. Your own headers
* Actions: MSGV Actions. Defining and using actions.
@end menu

@node MSGV Overview
@section Overview

An example message view:

@cartouche
@verbatim
    From: randy@epiphyte.com
    To: julia@eruditorum.org
    Subject: Re: some pics
    Flags: (seen attach)
    Date: Mon 19 Jan 2004 09:39:42 AM EET
    Maildir: /inbox
    Attachments(2): [1]DSCN4961.JPG(1.3M), [2]DSCN4962.JPG(1.4M)
     
    Hi Julia,
     
    Some pics from our trip to Cerin Amroth. Enjoy!
     
    All the best,
    Randy.
     
    On Sun 21 Dec 2003 09:06:34 PM EET, Julia wrote:
     
    [....]
@end verbatim
@end cartouche

Some notes:
@itemize
@item The variable @code{mu4e-view-fields} determines the header fields to be
shown; see @code{mu4e-header-info} for a list of built-in fields. Apart from
the built-in fields, you can also create custom fields using
@code{mu4e-header-info-custom}; see @ref{MSGV Custom headers}.
@item You can set the date format with the variable
@code{mu4e-date-format-long}.
@item By default, only the names of contacts in address fields are visible
(see @code{mu4e-view-show-addresses} to change this). You can view the e-mail
addresses by clicking on the name, or pressing @key{M-RET}.
@item You can compose a message for the contact at point by either clicking
@key{[mouse-2]} or pressing @key{C}.
@item The body text can be line-wrapped using @t{visual-line-mode}. @t{mu4e}
defines @key{w} to toggle between the wrapped and unwrapped state. If you want
to do this automatically when viewing a message, invoke @code{visual-line-mode}
in your @code{mu4e-view-mode-hook}.
@item For messages that support it, you can toggle between html and text versions using
@code{mu4e-view-toggle-html}, bound to @key{h};
@item You can hide cited parts
in messages (the parts starting with ``@t{>}'') using
@code{mu4e-view-hide-cited}, bound to @key{#}. If you want to do this
automatically for every message, invoke the function in your
@code{mu4e-view-mode-hook}.
@item For search-related operations, see @ref{Searching}.
@item You can scroll down the message using @key{SPC}; if you do this at the
end of a message,it automatically takes you to the next one. If you want to
prevent this behavior, set @code{mu4e-view-scroll-to-next} to @code{nil}.
@end itemize

@node MSGV Keybindings
@section Keybindings

You can find most things you can do with this message in the @emph{View} menu,
or by using the keyboard; the default bindings are:

@verbatim
key          description
==============================================================
n,p          view the next, previous message
],[          move to the next, previous unread message
y            select the headers view (if it's visible)

RET          scroll down
M-RET        open URL at point / attachment at point

SPC          scroll down, if at end, move to next message
S-SPC        scroll up

searching
---------
s            search
e            edit last query
/            narrow the search
b            search bookmark
B            edit bookmark before search
j            jump to maildir

M-left       previous query
M-right      next query

marking
-------
d            mark for moving to the trash folder
=            mark for removing trash flag ('untrash')
DEL,D        mark for complete deletion
m            mark for moving to another maildir folder
r            mark for refiling
+,-          mark for flagging/unflagging

u            unmark message at point
U            unmark *all* messages

%            mark based on a regular expression
T,t          mark whole thread, subthread

<insert>,*   mark for 'something' (decide later)
#            resolve deferred 'something' marks

x            execute actions for the marked messages

composition
-----------
R,F,C        reply/forward/compose
E            edit (only allowed for draft messages)

actions
-------
g            go to (visit) numbered URL (using `browse-url')
(or: <mouse-1> or M-RET with point on url)
C-u g visits multiple URLs
f            fetch (download )the numbered URL.
C-u f fetches multiple URLs
k            save the numbered URL in the kill-ring.
C-u k saves multiple URLs

e            extract (save) attachment (asks for number)
(or: <mouse-2> or S-RET with point on attachment)
C-u e extracts multiple attachments
o            open attachment (asks for number)
(or: <mouse-1> or M-RET with point on attachment)

a            execute some custom action on the message
A            execute some custom action on an attachment

misc
----
;            switch context
c            copy address at point (with C-u copy long version)

h            toggle between html/text (if available)
w            toggle line wrapping
#            toggle show/hide cited parts

v            show details about the cryptographic signature

.            show the raw message view. 'q' takes you back.
C-+,C--      increase / decrease the number of headers shown
H            get help
C-S-u        update mail & reindex
q            leave the message view
@end verbatim

For the marking commands, please refer to @ref{Marking messages}.

@node Attachments
@section Attachments

By default, @t{mu4e} uses the @t{xdg-open}-program
@footnote{@url{http://portland.freedesktop.org/wiki/}} or (on OS X) the
@t{open} program for opening attachments. If you want to use another
program, you do so by setting the @t{MU_PLAY_PROGRAM} environment
variable to the program to be used.

The default directory for extracting (saving) attachments is your home
directory (@file{~/}); you can change this using the variable
@code{mu4e-attachment-dir}, for example:

@lisp
(setq mu4e-attachment-dir  "~/Downloads")
@end lisp

For more flexibility, @code{mu4e-attachment-dir} can also be a user-provided
function. This function receives two parameters: the file-name and the
mime-type as found in the e-mail message@footnote{sadly, often
@t{application/octet-stream} is used for the mime-type, even if a better type
is available} of the attachment, either or both of which can be @t{nil}. For
example:

@lisp
(setq mu4e-attachment-dir
  (lambda (fname mtype)
     (cond
        ;; docfiles go to ~/Desktop
       ((and fname (string-match "\\.doc$" fname))  "~/Desktop")
       ;; ... other cases  ...
       (t "~/Downloads")))) ;; everything else
@end lisp

You can extract multiple attachments at once by prefixing the extracting
command by @key{C-u}; so @kbd{C-u e} asks you for a range of attachments to
extract (for example, @kbd{1 3-6 8}). The range "@samp{a}" is a shortcut for
@emph{all} attachments.

@node Viewing images inline
@section Viewing images inline

It is possible to show images inline in the message view buffer if you run
@command{emacs} in GUI-mode. You can enable this by setting the variable
@code{mu4e-view-show-images} to @t{t}. Since @command{emacs} does not always
handle images correctly, this is not enabled by default. If you are using
@command{emacs} 24 with
@emph{ImageMagick}@footnote{@url{http://www.imagemagick.org}} support, make
sure you call @code{imagemagick-register-types} in your configuration, so it
is used for images.

@lisp
;; enable inline images
(setq mu4e-view-show-images t)
;; use imagemagick, if available
(when (fboundp 'imagemagick-register-types)
  (imagemagick-register-types))
@end lisp

@node Displaying rich-text messages
@section Displaying rich-text messages

@t{mu4e} normally prefers the plain-text version for messages that
consist of both a plain-text and html (rich-text) versions of the
body-text. You can change this by setting @code{mu4e-view-prefer-html}
to @t{t}. And you can toggle this value (globally) using @kbd{h} in the
message view; this also refreshes the message with the new setting.

Note, when using html-based rendering, you don't get the hyperlink
shortcuts the text-version provides.

If there is only an html-version, or if the plain-text version is too
short in comparison with the html part@footnote{this is e.g. for the
case where the text-part is only a short blurb telling you to use the
html-version; see @code{mu4e-view-html-plaintext-ratio-heuristic}},
@t{mu4e} tries to convert the html into plain-text for display.

With emacs 24.4 or newer, this defaults to @code{mu4e-shr2text}, which
uses the built-in @t{shr} renderer. For older emacs versions, this
defaults to the built-in @code{html2text} function. In practice, the
latter gives much better results.

If you use @code{mu4e-shr2text}, it might be useful to emulate some of
the @t{shr} key bindings, with something like:
@lisp
(add-hook 'mu4e-view-mode-hook
  (lambda()
    ;; try to emulate some of the eww key-bindings
    (local-set-key (kbd "<tab>") 'shr-next-link)
    (local-set-key (kbd "<backtab>") 'shr-previous-link)))
@end lisp

If you're using a dark theme, and the messages are hard to read, it can help to change
the luminosity, e.g.:
@lisp
(setq shr-color-visible-luminance-min 80)
@end lisp

If your emacs does not have @t{shr} yet, it can be useful to use a
custom method. For that, you can set the variable
@code{mu4e-html2text-command} to either a shell command or a function
instead.

@subsection Html2text commands

If @code{mu4e-html2text-command} is a shell command, it is expected to
take html from standard input and write plain text in @t{UTF-8} encoding
on standard output.

An example of such a program is the program that is actually
@emph{called}
@t{html2text}@footnote{@url{http://www.mbayer.de/html2text/}}. After
installation, you can set it up with something like the following:

@lisp
(setq mu4e-html2text-command "html2text -utf8 -width 72")
@end lisp

An alternative to this is the Python @t{python-html2text} package; after
installing that, you can tell @t{mu4e} to use it with something like:

@lisp
(setq mu4e-html2text-command
  "html2markdown | grep -v '&nbsp_place_holder;'")
@end lisp

On OS X, there is a program called @t{textutil} as yet another
alternative:

@lisp
(setq mu4e-html2text-command
  "textutil -stdin -format html -convert txt -stdout")
@end lisp

@subsection Html2text functions
@anchor{Html2text functions}

If @code{mu4e-html2text-command} refers to an elisp function, the
function is expected to take a message plist as its input, and returns
the transformed data.


You can easily create your own function, for instance:

@lisp
(defun my-mu4e-html2text (msg)
  "My html2text function; shows short message inline, show
long messages in some external browser (see `browse-url-generic-program')."
  (let ((html (or (mu4e-message-field msg :body-html) "")))
    (if (> (length html) 20000)
      (progn
	(mu4e-action-view-in-browser msg)
	"[Viewing message in external browser]")
      (mu4e-shr2text msg))))

(setq mu4e-html2text-command 'my-mu4e-html2text)
@end lisp

@subsection Privacy aspects
@anchor{Privacy aspects}

When opening your messages in a graphical browser, it may expose you
doing so to the sender, due to the presence of specially crafted image
URLs, or Javascript.

If that is an issue, it is recommended to use a browser (or browser
profile) that does not load images. The same applies to Javascript.


@node MSGV Crypto
@section Crypto

The @t{mu4e} message view supports@footnote{Crypto-support in @t{mu4e}
requires @t{mu} to have been build with crypto-support; see the
@ref{FAQ}} decryption of encrypted messages, as well as verification of
signatures. For signing/encrypting messages your outgoing messages, see
@ref{Signing and encrypting}.

Currently, only PGP/MIME is supported; PGP-inline and S/MIME are not.

For all of this to work, @command{gpg-agent} must be running, and it
must set the environment variable @t{GPG_AGENT_INFO}. You can check from
@command{emacs} with @key{M-x getenv GPG_AGENT_INFO}.

In many mainstream Linux/Unix desktop environments, everything works
out-of-the-box, but if your environment does not automatically start
@command{gpg-agent}, you can do so by hand:
@verbatim
$ eval $(gpg-agent --daemon)
@end verbatim

@noindent
This starts the daemon, and sets the environment variable.

@subsection Decryption
@anchor{Decryption}

If you receive messages that are encrypted (using PGP/MIME), @t{mu4e} can try
to decrypt them, base on the setting of @code{mu4e-decryption-policy}. If you
set it to @t{t}, @t{mu4e} attempts to decrypt messages automatically; this is
the default. If you set it to @t{nil}, @t{mu4e} @emph{won't} attempt to
decrypt anything. Finally, if you set it to @t{'ask}, it asks you what to do,
each time an encrypted message is encountered.

When opening an encrypted message, @t{mu} consults @t{gpg-agent} to see if it
already has unlocked the key needed to decrypt the message; if not, it prompts
you for a password (typically with a separate top-level window). This is only
needed once per session.

@subsection Verifying signatures
@anchor{Verifying signatures}

Some e-mail messages are cryptographically signed, and @t{mu4e} can check the
validity of these signatures. If a message has one or more signatures, the
message view shows an extra header @t{Signature:} (assuming it is part of your
@code{mu4e-view-fields}), and one or more `verdicts' of the signatures found;
either @t{verified}, @t{unverified} or @t{error}. For instance:

@verbatim
Signature: unverified (Details)
@end verbatim
or
@verbatim
Signature: verified Darrow Andromedus <darrow@rising.com> (Details)
@end verbatim

You can see the details of the signature verification by activating the
@t{Details} or pressing @key{v}. This pops up a little window with the
details of the signatures found and whether they could be verified or
not.

Note that @t{mu4e} does not check whether the signer is the same as the
sender of the message, since this would cause too many false negatives
for senders that use an address that is not part of their certificate.
Also, the From: address can easily be forged.

For more information, see the @command{mu-verify} manual page.

@node MSGV Custom headers
@section Custom headers

Sometimes the normal headers that @t{mu4e} offers (Date, From, To, Subject
etc.) may not be enough. For these cases, @t{mu4e} offers @emph{custom
headers} in both the headers-view and the message-view.

See @ref{HV Custom headers} for an example of this; the difference for the
message-view is that you should add your custom header to
@code{mu4e-view-fields} rather than @code{mu4e-headers-fields}.

@node MSGV Actions
@section Actions

You can perform custom functions (``actions'') on messages and their
attachments. For a general discussion on how to define your own, see
@ref{Actions}.

@subsection Message actions
@code{mu4e-view-action} (@key{a}) lets you pick some custom action to perform
on the current message. You can specify these actions using the variable
@code{mu4e-view-actions}; @t{mu4e} defines a number of example actions.

@subsection Attachment actions
Similarly, there is @code{mu4e-view-attachment-action} (@key{A}) for actions
on attachments, which you can specify with
@code{mu4e-view-attachment-actions}.

@t{mu4e} predefines a number of attachment-actions:
@itemize
@item @t{open-with} (@key{w}): open the attachment with some arbitrary
program. For example, suppose you have received a message with a picture
attachment; then, @kbd{A w 1 RET gimp RET} opens that attachment in @emph{The
Gimp}
@item @t{pipe} (@key{|}: process the attachment with some Unix shell-pipe and
see the results. Suppose you receive a patch file, and would like to get an
overview of the changes, using the @t{diffstat} program. You can use something
like: @kbd{A | 1 RET diffstat -b RET}.
@item @command{emacs} (@key{e}): open the attachment in your running @command{emacs}. For
example, if you receive some text file you'd like to open in @command{emacs}:
@kbd{A e 1 RET}.
@end itemize

These actions all work on a @emph{temporary copy} of the attachment.

@node Editor view
@chapter The editor view

Writing e-mail messages takes place in the Editor View. @t{mu4e}'s editor view
builds on top of Gnus' @t{message-mode}. Most of the @t{message-mode}
functionality is available, as well some @t{mu4e}-specifics. Its major mode is
@code{mu4e-compose-mode}.

@menu
* Overview: EV Overview. What is the Editor view
* Keybindings: EV Keybindings. Doing things with your keyboard
* Address autocompletion:: Quickly entering known addresses
* Compose hooks::Calling functions when composing
* Signing and encrypting:: Support for cryptography
* Queuing mail:: Sending mail when the time is ripe
* Message signatures:: Adding your personal footer to messages
* Other settings::Miscellanea
@end menu

@node EV Overview
@section Overview

@cartouche
@verbatim
    From: Rupert the Monkey <rupert@example.com>
    To: Wally the Walrus <wally@example.com>
    Subject: Re: Eau-qui d'eau qui?
    --text follows this line--
     
    On Mon 16 Jan 2012 10:18:47 AM EET, Wally the Walrus wrote:
     
    > Hi Rupert,
    >
    > Dude - how are things?
    >
    > Later -- wally.
@end verbatim
@end cartouche


@node EV Keybindings
@section Keybindings

@t{mu4e}'s editor view derives from Gnus' message editor and shares most of
its keybindings. Here are some of the more useful ones (you can use the menu
to find more):

@verbatim
key          description
---          -----------
C-c C-c      send message
C-c C-d      save to drafts and leave
C-c C-k      kill the message buffer (the message remains in the draft folder)
C-c C-a      attach a file (pro-tip: drag & drop works as well)

(mu4e-specific)
C-S-u        update mail & reindex
@end verbatim

@node Address autocompletion
@section Address autocompletion

@t{mu4e} supports@footnote{@command{emacs} 23.2 or higher is required}
autocompleting addresses when composing e-mail messages. @t{mu4e} uses the
e-mail addresses from the messages you sent or received as the source for
this. Address auto-completion is enabled by default; if you want to disable it
for some reason, set @t{mu4e-compose-complete-addresses} to @t{nil}.

Emacs 24 also supports cycling through the alternatives. When there are more
than @emph{5} matching addresses, they are shown in a @t{*Completions*}
buffer. Once the number of matches gets below this number, one is inserted in
the address field and you can cycle through the alternatives using @key{TAB}.

@subsection Limiting the number of addresses

If you have a lot of mail, especially from mailing lists and the like, there
can be a @emph{lot} of e-mail addresses, many of which may not be very useful
when auto-completing. For this reason, @t{mu4e} attempts to limit the number
of e-mail addresses in the completion pool by filtering out the ones that are
not likely to be relevant. The following variables are available for tuning
this:

@itemize
@item @code{mu4e-compose-complete-only-personal} --- when set to @t{t},
only consider addresses that were seen in @emph{personal} messages --- that is,
messages in which one of my e-mail addresses was seen in one of the address
fields. This is to exclude mailing list posts. You can define what is
considered `my e-mail address' using @code{mu4e-user-mail-address-list}, a
list of e-mail address (defaults to @code{user-mail-address}, and when
indexing from the command line, the @t{--my-address} parameter for @t{mu
index}.
@item @code{mu4e-compose-complete-only-after} --- only consider e-mail
addresses last seen after some date. Parameter is a string, parseable by
@code{org-parse-time-string}. This excludes old e-mail addresses. The default
is @t{"2010-01-01"}, i.e., only consider e-mail addresses seen since the start
of 2010.
@item @code{mu4e-compose-complete-ignore-address-regexp} --- a regular expression to
filter out other `junk' e-mail addresses; defaults to ``@t{no-?reply}''.
@end itemize

@node Compose hooks
@section Compose hooks

If you want to change some setting, or execute some custom action before
message composition starts, you can define a @emph{hook function}. @t{mu4e}
offers two hooks:
@itemize
@item @code{mu4e-compose-pre-hook}: this hook is run @emph{before} composition
starts; if you are composing a @emph{reply}, @emph{forward} a message, or
@emph{edit} an existing message, the variable
@code{mu4e-compose-parent-message} points to the message being replied to,
forwarded or edited, and you can use @code{mu4e-message-field} to get the
value of various properties (and see @ref{Message functions}).
@item @code{mu4e-compose-mode-hook}: this hook is run just before composition
starts, when the whole buffer has already been set up. This is a good place
for editing-related settings. @code{mu4e-compose-parent-message} (see above)
is also at your disposal.
@end itemize

@noindent
Let's look at some examples. First, suppose we want to set the
@t{From:}-address for a reply message based on the receiver of the original:
@lisp
;; 1) messages to me@@foo.example.com should be replied with From:me@@foo.example.com
;; 2) messages to me@@bar.example.com should be replied with From:me@@bar.example.com
;; 3) all other mail should use From:me@@cuux.example.com
(add-hook 'mu4e-compose-pre-hook
  (defun my-set-from-address ()
    "Set the From address based on the To address of the original."
    (let ((msg mu4e-compose-parent-message)) ;; msg is shorter...
      (when msg
	(setq user-mail-address
	  (cond
	    ((mu4e-message-contact-field-matches msg :to "me@@foo.example.com")
	      "me@@foo.example.com")
	    ((mu4e-message-contact-field-matches msg :to "me@@bar.example.com")
	      "me@@bar.example.com")
	    (t "me@@cuux.example.com")))))))
@end lisp

Second, as mentioned, @code{mu4e-compose-mode-hook} is especially useful for
editing-related settings. For example:
@lisp
(add-hook 'mu4e-compose-mode-hook
  (defun my-do-compose-stuff ()
    "My settings for message composition."
    (set-fill-column 72)
    (flyspell-mode)))
@end lisp

This hook is also useful for adding headers or changing headers, since the
message is fully formed when this hook runs. For example, to add a
@t{Bcc:}-header, you could add something like the following, using
@code{message-add-header} from @code{message-mode}.

@lisp
(add-hook 'mu4e-compose-mode-hook
  (defun my-add-bcc ()
    "Add a Bcc: header."
    (save-excursion (message-add-header "Bcc: me@@example.com\n"))))
@end lisp

@noindent
For a more general discussion about extending @t{mu4e}, see @ref{Extending
mu4e}.

@node Signing and encrypting
@section Signing and encrypting

Signing and encrypting of messages is possible using @t{emacs-mime}
(@inforef{Composing,,emacs-mime}), most easily accessed through the
@t{Attachments}-menu while composing a message, or with @kbd{M-x
mml-secure-message-encrypt-pgp}, @kbd{M-x mml-secure-message-sign-pgp}.

The support for encryption and signing is @emph{independent} of the support
for their counterparts, decrypting and signature verification (as discussed in
@ref{MSGV Crypto}). Even if your @t{mu4e} does not have support for the latter
two, you can still sign/encrypt messages.

Currently, decryption and signature verification only works for PGP/MIME;
inline-PGP and S/MIME are not supported.

Important note: the messages are encrypted when they are @emph{sent}:
this means that draft messages are @emph{not} encrypted. So if you are
using e.g. @t{offlineimap} or @t{mbsync} to synchronize with some remote
IMAP-service, make sure the drafts folder is @emph{not} in the set of
synchronized folders, for obvious reasons.

@node Queuing mail
@section Queuing mail

If you cannot send mail right now, for example because you are currently
offline, you can @emph{queue} the mail, and send it when you have restored
your internet connection. You can control this from the @ref{Main view}.

To allow for queuing, you need to tell @t{smtpmail} where you want to store
the queued messages. For example:

@lisp
(setq smtpmail-queue-mail t  ;; start in queuing mode
  smtpmail-queue-dir   "~/Maildir/queue/cur")
@end lisp

For convenience, we put the queue directory somewhere in our normal
maildir. If you want to use queued mail, you should create this directory
before starting @t{mu4e}. The @command{mu mkdir} command may be useful here,
so for example:

@verbatim
  $ mu mkdir ~/Maildir/queue
  $ touch ~/Maildir/queue/.noindex
@end verbatim

The file created by the @command{touch} command tells @t{mu} to ignore this
directory for indexing, which makes sense since it contains @t{smtpmail}
meta-data rather than normal messages; see the @t{mu-mkdir} and @t{mu-index}
man-pages for details.

@emph{Warning}: when you switch on queued-mode, your messages @emph{won't}
reach their destination until you switch it off again; so, be careful not to
do this accidentally!

@node Message signatures
@section Message signatures

Message signatures are the standard footer blobs in e-mail messages where you
can put in information you want to include in every message. The text to
include is set with @code{mu4e-compose-signature}.

If you don't want to include this automatically with each message,
you can set @code{mu4e-compose-signature-auto-include} to @code{nil}; you can
then still include the signature manually, using the function
@code{message-insert-signature}, typically bound to @kbd{C-c C-w}.

@node Other settings
@section Other settings

@itemize
@item If you want use @t{mu4e} as @command{emacs}' default program for sending mail,
see @ref{Emacs default}.
@item Normally, @t{mu4e} @emph{buries} the message buffer after sending; if you want
to kill the buffer instead, add something like the following to your
configuration:
@lisp
(setq message-kill-buffer-on-exit t)
@end lisp
@item If you want to exclude your own e-mail address when ``replying to
all'', set @code{mu4e-compose-dont-reply-to-self} to @code{t}.  In order
for this to work properly you need to properly set the
@code{user-mail-address} variable or in the case you use multiple e-mail
addresses you need to set the @code{mu4e-user-mail-address-list}
variable accordingly.
@end itemize

@node Searching
@chapter Searching

@t{mu4e} is fully search-based: even if you `jump to a folder', you are
executing a query for messages that happen to have the property of being in a
certain folder (maildir).

Normally, queries return up to @code{mu4e-headers-results-limit} (default:
500) results. That is usually more than enough, and makes things significantly
faster. Sometimes, however, you may want to show @emph{all} results; you can
enable this with @kbd{M-x mu4e-headers-toggle-full-search}, or by customizing
the variable @code{mu4e-headers-full-search}. This applies to all search
commands.

You can also influence the sort order and whether threads are shown or not;
see @ref{Sorting and threading}.

@menu
* Queries:: Searching for messages.
* Bookmarks:: Remembering queries.
* Maildir searches:: Queries for maildirs.
* Other search functionality:: Some more tricks.
@end menu

@node Queries
@section Queries

@t{mu4e} queries are the same as the ones that @t{mu find}
understands@footnote{with the caveat that command-line queries are
subject to the shell's interpretation before @t{mu} sees them}. Let's
look at some examples here; you can consult the @code{mu-query} man page
for the details.

@itemize

@item Get all messages regarding @emph{bananas}:
@verbatim
bananas
@end verbatim

@item Get all messages regarding @emph{bananas} from @emph{John} with an attachment:
@verbatim
from:john and flag:attach and bananas
@end verbatim

@item Get all messages with subject @emph{wombat} in June 2017
@verbatim
subject:wombat and date:20170601..20170630
@end verbatim

@item Get all messages with PDF attachments in the @t{/projects} folder
@verbatim
maildir:/projects and mime:application/pdf
@end verbatim

@item Get all messages about @emph{Rupert} in the @t{/Sent Items} folder. Note that
maildirs with spaces must be quoted.
@verbatim
"maildir:/Sent Items" and rupert
@end verbatim

@item Get all important messages which are signed:
@verbatim
flag:signed and prio:high
@end verbatim

@item Get all messages from @emph{Jim} without an attachment:
@verbatim
from:jim and not flag:attach
@end verbatim

@item Get all messages with Alice in one of the contacts-fields (@t{to}, @t{from},
@t{cc}, @t{bcc}):
@verbatim
contact:alice
@end verbatim

@item Get all unread messages where the subject mentions Ångström: (search is
case-insensitive and accent-insensitive, so this matches Ångström, angstrom,
aNGstrøM, ...)
@verbatim
subject:Ångström and flag:unread
@end verbatim

@item Get all unread messages between Mar-2012 and Aug-2013 about some bird:
@verbatim
date:20120301..20130831 and nightingale and flag:unread
@end verbatim

@item Get today's messages:
@verbatim
date:today..now
@end verbatim

@item Get all messages we got in the last two weeks regarding @emph{emacs}:
@verbatim
date:2w.. and emacs
@end verbatim

@item Get messages from the @emph{Mu} mailing list:
@verbatim
list:mu-discuss.googlegroups.com
@end verbatim

Note --- in the @ref{Headers view} you may see the `friendly name' for a
list; however, when searching you need the real name. You can see the
real name for a mailing list from the friendly name's tool-tip.

@item Get messages with a subject soccer, Socrates, society, ...; note that
the `*'-wildcard can only appear as a term's rightmost character:
@verbatim
subject:soc*
@end verbatim

@item Get all messages @emph{not} sent to a mailing-list:
@verbatim
NOT flag:list
@end verbatim

@item Get all mails with attachments with filenames starting with @emph{pic}; note
that the `*' wildcard can only appear as the term's rightmost character:
@verbatim
file:pic*
@end verbatim

@item Get all messages with PDF-attachments:
@verbatim
mime:application/pdf
@end verbatim

Get all messages with image attachments, and note that the `*' wildcard can
only appear as the term's rightmost character:
@verbatim
mime:image/*
@end verbatim

@end itemize

@node Bookmarks
@section Bookmarks

If you have queries that you use often, you may want to store them as
@emph{bookmarks}. Bookmark searches are available in the main view
(@pxref{Main view}), header view (@pxref{Headers view}), and message
view (@pxref{Message view}), using (by default) the key @key{b}
(@kbd{M-x mu4e-search-bookmark}), or @key{B} (@kbd{M-x
mu4e-search-bookmark-edit}) which lets you edit the bookmark first.

@subsection Setting up bookmarks

@t{mu4e} provides a number of default bookmarks. Their definition is
instructive:

@lisp
(defvar mu4e-bookmarks
  `( ,(make-mu4e-bookmark
	:name  "Unread messages"
	:query "flag:unread AND NOT flag:trashed"
	:key ?u)
     ,(make-mu4e-bookmark
	:name "Today's messages"
	:query "date:today..now"
	:key ?t)
     ,(make-mu4e-bookmark
	:name "Last 7 days"
	:query "date:7d..now"
	:key ?w)
     ,(make-mu4e-bookmark
	:name "Messages with images"
	:query "mime:image/*"
	:key ?p))
  "A list of pre-defined queries. Each query is represented by a
mu4e-bookmark structure with parameters @t{:name} with the name
of the bookmark, @t{:query} with the query expression (a query
string or an s-expression that evaluates to query string) and a
@t{:key}, which is the shortcut-key for the query.

An older form of bookmark, a 3-item list with (QUERY DESCRIPTION
KEY) is still recognized as well, for backward-compatibility.")
@end lisp

You can replace these or add your own items, by putting in your
configuration (@file{~/.emacs}) something like:
@lisp
(add-to-list 'mu4e-bookmarks
  (make-mu4e-bookmark
    :name  "Big messages"
    :query "size:5M..500M"
    :key ?b))
 @end lisp

This prepends your bookmark to the list, and assigns the key @key{b} to it. If
you want to @emph{append} your bookmark, you can use @code{t} as the third
argument to @code{add-to-list}.

In the various @t{mu4e} views, pressing @key{b} lists all the bookmarks
defined in the echo area, with the shortcut key highlighted. So, to invoke the
bookmark we just defined (to get the list of "Big Messages"), all you need to
type is @kbd{bb}.

@subsection Lisp expressions as bookmarks

Instead of using strings, it is also possible to use Lisp expressions as
bookmarks. The only requirement is that they evaluate to a query string.

For example, to get all the messages that are at most a week old in your
inbox:

@lisp
(add-to-list 'mu4e-bookmarks
  (make-mu4e-bookmark
   :name  "Inbox messages in the last 7 days"
   :query (concat "maildir:/inbox AND date:"
             (format-time-string "%Y%m%d"
                (subtract-time (current-time) (days-to-time 7))))
   :key ?w) t)
@end lisp

@subsection Editing bookmarks before searching

There is also @kbd{M-x mu4e-headers-search-bookmark-edit} (key @key{B}), which
lets you edit the bookmarked query before invoking it. This can be useful if
you have many similar queries, but need to change some parameter. For example,
you could have a bookmark @samp{"date:today..now AND "}@footnote{Not a valid
search query by itself}, which limits any result to today's messages.

@node Maildir searches
@section Maildir searches

Maildir searches are quite similar to bookmark searches (see @ref{Bookmarks}),
with the difference being that the target is always a maildir --- maildir
queries provide a `traditional' folder-like interface to a search-based e-mail
client. By default, maildir searches are available in the @ref{Main view},
@ref{Headers view}, and @ref{Message view}, with the key @key{j}
(@code{mu4e-jump-to-maildir}).

@subsection Setting up maildir shortcuts

You can search for maildirs like any other message property
(e.g. with a query like @t{maildir:/myfolder}), but since it is so common,
@t{mu4e} offers a shortcut for this.

For this to work, you need to set the variable @code{mu4e-maildir-shortcuts}
to the list of maildirs you want to have quick access to, for example:

@lisp
(setq mu4e-maildir-shortcuts
  '( ("/inbox"     . ?i)
     ("/archive"   . ?a)
     ("/lists"     . ?l)
     ("/work"      . ?w)
     ("/sent"      . ?s)))
@end lisp

This sets @key{i} as a shortcut for the @t{/inbox} folder --- effectively a
query @t{maildir:/inbox}. There is a special shortcut @key{o} or @key{/} for
@emph{other} (so don't use those for your own shortcuts!), which allows you to
choose from @emph{all} maildirs that you have. There is support for
autocompletion; note that the list of maildirs is determined when @t{mu4e}
starts; if there are changes in the maildirs while @t{mu4e} is running, you
need to restart @t{mu4e}.

Each of the folder names is relative to your top-level maildir directory; so
if you keep your mail in @file{~/Maildir}, @file{/inbox} would refer to
@file{~/Maildir/inbox}. With these shortcuts, you can jump around your
maildirs (folders) very quickly --- for example, getting to the @t{/lists}
folder only requires you to type @kbd{jl}, then change to @t{/work} with
@kbd{jw}.

While in queries you need to quote folder names (maildirs) with spaces in
them, you should @emph{not} quote them when used in
@code{mu4e-maildir-shortcuts}, since @t{mu4e} does that automatically for you.

The very same shortcuts are used by @kbd{M-x mu4e-mark-for-move} (default
shortcut @key{m}); so, for example, if you want to move a message to the
@t{/archive} folder, you can do so by typing @kbd{ma}.

@node Other search functionality
@section Other search functionality

@subsection Navigating through search queries
You can navigate through previous/next queries using
@code{mu4e-headers-query-prev} and @code{mu4e-headers-query-next}, which are
bound to @key{M-left} and @key{M-right}, similar to what some web browsers do.

@t{mu4e} tries to be smart and not record duplicate queries. Also, the number
of queries remembered has a fixed limit, so @t{mu4e} won't use too much
memory, even if used for a long time. However, if you want to forget
previous/next queries, you can use @kbd{M-x mu4e-headers-forget-queries}.

@subsection Narrowing search results

It can be useful to narrow existing search results, that is, to add some
clauses to the current query to match fewer messages.

For example, suppose you're looking at some mailing list, perhaps by
jumping to a maildir (@kbd{M-x mu4e-headers-jump-to-maildir}, @key{j}) or
because you followed some bookmark (@kbd{M-x mu4e-headers-search-bookmark},
@key{b}). Now, you want to narrow things down to only those messages that have
attachments.

This is when @kbd{M-x mu4e-headers-search-narrow} (@key{/}) comes in handy. It
asks for an additional search pattern, which is appended to the current search
query, in effect getting you the subset of the currently shown headers that
also match this extra search pattern. @key{\} takes you back to the previous
query, so, effectively `widens' the search. Technically, narrowing the results
of query @t{x} with expression @t{y} implies doing a search @t{(x) AND (y)}.

Note that messages that were not in your original search results because
of @code{mu4e-headers-results-limit} may show up in the narrowed query.

@subsection Including related messages
@anchor{Including related messages}

It can be useful to not only show the messages that directly match a certain
query, but also include messages that are related to these messages. That is,
messages that belong to the same discussion threads are included in the
results, just like e.g. Gmail does it. You can enable this behavior by setting
@code{mu4e-headers-include-related} to @code{t}, and you can toggle between
including/not-including with @key{W}.

Be careful though when e.g. deleting ranges of messages from a certain
folder --- the list may now also include messages from @emph{other}
folders.

@subsection Skipping duplicates
@anchor{Skipping duplicates}

Another useful feature is skipping of @emph{duplicate messages}. When you have
copies of messages, there's usually little value in including more than one in
search results. A common reason for having multiple copies of messages is the
combination of Gmail and @t{offlineimap}, since that is the way the labels /
virtual folders in Gmail are represented. You can enable skipping duplicates
by setting @code{mu4e-headers-skip-duplicates} to @code{t}, and you can toggle
between the skipping/not skipping with @key{V}.

Note, messages are considered duplicates when they have the same
@t{Message-Id}.

@node Marking
@chapter Marking

In @t{mu4e}, the common way to do things with messages is a two-step process -
first you @emph{mark} them for a certain action, then you @emph{execute}
(@key{x}) those marks. This is similar to the way @t{dired} operates. Marking
can happen in both the @ref{Headers view} and the @ref{Message view}.

@menu
* Marking messages::Selecting message do something with them
* What to mark for::What can we do with them
* Executing the marks::Do it
* Leaving the headers buffer::Handling marks automatically when leaving
* Built-in marking functions::Helper functions for dealing with them
* Custom mark functions::Define your own mark function
* Adding a new kind of mark::Adding your own marks
@end menu

@node Marking messages
@section Marking messages

There are multiple ways to mark messages:
@itemize
@item @emph{message at point}: you can put a mark on the message-at-point in
either the @ref{Headers view} or @ref{Message view}
@item @emph{region}: you can put a mark on all messages in the current region
(selection) in the @ref{Headers view}
@item @emph{pattern}: you can put a mark on all messages in the @ref{Headers
view} matching a certain pattern with @kbd{M-x mu4e-headers-mark-pattern}
(@key{%})
@item @emph{thread/subthread}: You can put a mark on all the messages in the
thread/subthread at point with @kbd{M-x mu4e-headers-mark-thread} and @kbd{M-x
mu4e-headers-mark-subthread}, respectively
@end itemize

@node What to mark for
@section What to mark for

@t{mu4e} supports a number of marks:

@cartouche
@verbatim
mark for/as  | keybinding  | description
-------------+-------------+------------------------------
'something'  | *, <insert> | mark now, decide later
delete       | D, <delete> | delete
flag         | +           | mark as 'flagged' ('starred')
move         | m           | move to some maildir
read         | !           | mark as read
refile       | r           | mark for refiling
trash        | d           | move to the trash folder
untrash      | =           | remove 'trash' flag
unflag       | -           | remove 'flagged' mark
unmark       | u           | remove mark at point
unmark all   | U           | remove all marks
unread       | ?           | marks as unread
action       | a           | apply some action
@end verbatim
@end cartouche

After marking a message, the left-most columns in the headers view indicate
the kind of mark. This is informative, but if you mark many (say, thousands)
messages, this slows things down significantly@footnote{this uses an
@command{emacs} feature called @emph{overlays}, which are slow when used a lot
in a buffer}. For this reason, you can disable this by setting
@code{mu4e-headers-show-target} to @code{nil}.

@t{something} is a special kind of mark; you can use it to mark messages
for `something', and then decide later what the `something' should
be@footnote{This kind of `deferred marking' is similar to the facility
in @t{dired}, @t{midnight commander}
(@url{http://www.midnight-commander.org/}) and the like, and uses the
same key binding (@key{insert}).}  Later, you can set the actual mark
using @kbd{M-x mu4e-mark-resolve-deferred-marks}
(@key{#}). Alternatively, @t{mu4e} will ask you when you try to execute
the marks (@key{x}).

@node Executing the marks
@section Executing the marks

After you have marked some messages, you can execute them with @key{x}
(@kbd{M-x mu4e-mark-execute-all}).

A hook, @code{mu4e-mark-execute-pre-hook}, is available which is run
right before execution of each mark. The hook is called with two
arguments, the mark and the message itself.

@node Leaving the headers buffer
@section Leaving the headers buffer

When you quit or update a headers buffer that has marked messages (for
example, by doing a new search), @t{mu4e} asks you what to do with them,
depending on the value of the variable @code{mu4e-headers-leave-behavior} ---
see its documentation.

@node Built-in marking functions
@section Built-in marking functions

Some examples of @t{mu4e}'s built-in marking functions.

@itemize
@item @emph{Mark the message at point for trashing}: press @key{d}
@item @emph{Mark all messages in the buffer as unread}: press @kbd{C-x h o}
@item @emph{Delete the messages in the current thread}: press @kbd{T D}
@item @emph{Mark messages with a subject matching ``hello'' for flagging}:
press @kbd{% s hello RET}.
@end itemize

@node Custom mark functions
@section Custom mark functions

Sometimes, the built-in functions to mark messages may not be sufficient for
your needs. For this, @t{mu4e} offers an easy way to define your own custom
mark functions. You can choose one of the custom marker functions by pressing
@key{&} in the @ref{Headers view} and @ref{Message view}.

Custom mark functions are to be appended to the list
@code{mu4e-headers-custom-markers}. Each of the elements of this list
('markers') is a list with two or three elements:
@enumerate
@item The name of the marker --- a short string describing this marker. The
first character of this string determines its shortcut, so these should be
unique. If necessary, simply prefix the name with a unique character.
@item a predicate function, taking two arguments @var{msg} and @var{param}.
@var{msg} is the message plist (see @ref{Message functions}) and @var{param} is
a parameter provided by the third of the marker elements (see the next
item). The predicate function should return non-@t{nil} if the message
matches.
@item (optionally) a function that is evaluated once, and the result is passed as a
parameter to the predicate function. This is useful when user-input is needed.
@end enumerate

Let's look at an example: suppose we want to match all messages that have more
than @emph{n} recipients --- we could do this with the following recipe:

@lisp
(add-to-list 'mu4e-headers-custom-markers
  '("More than n recipients"
     (lambda (msg n)
       (> (+ (length (mu4e-message-field msg :to))
	    (length (mu4e-message-field msg :cc))) n))
     (lambda ()
       (read-number "Match messages with more recipients than: "))) t)
@end lisp

After evaluating this expression, you can use it by pressing @key{&} in
the headers buffer to select a custom marker function, and then @key{M}
to choose this particular one (@t{M} because it is the first character
of the description).

As you can see, it's not very hard to define simple functions to match
messages. There are more examples in the defaults for
@code{mu4e-headers-custom-markers}; see @file{mu4e-headers.el} and see
@ref{Extending mu4e} for general information about writing your own functions.


@node Adding a new kind of mark
@section Adding a new kind of mark

It is possible to configure new marks. To do so, one can add entries
in the list @code{mu4e-marks}. Such an element must have the following form:

@lisp
(SYMBOL
  :char STRING
  :prompt STRING
  :ask-target (lambda () TARGET)
  :dyn-target (lambda (TARGET MSG) DYN-TARGET)
  :show-target (lambda (DYN-TARGET) STRING)
  :action (lambda (DOCID MSG DYN-TARGET) nil))
@end lisp

The symbol can be any symbol, except for @code{'unmark} and
@code{'something}, which are reserved. The rest is a plist with the
following elements:

@itemize
@item @code{:char} --- the character to display in the headers view.
@item @code{:prompt} --- the prompt to use when asking for marks
(used for example when marking a whole thread).
@item @code{:ask-target} --- a function run once per bulk-operation, and thus suitable for
querying the user about a target for move-like marks. If @t{nil}, the
@t{TARGET} passed to @code{:dyn-target} is @t{nil}.
@item @code{:dyn-target} --- a function run once per message
(The message is passed as @t{MSG} to the function). This function allows
to compute a per-message target, for refile-like marks. If @t{nil}, the
@t{DYN-TARGET} passed to the @code{:action} is the @t{TARGET} obtained as above.
@item @code{:show-target} --- how to display the target in the headers view.
If @code{:show-target} is @t{nil} the @t{DYN-TARGET} is shown (and
@t{DYN-TARGET} must be a string).
@item @code{:action} --- the action to apply on the message when the mark is executed.
@end itemize

As an example, suppose we would like to add a mark for tagging
messages (GMail-style), then we can run the following code (after
loading @t{mu4e}):

@lisp
(add-to-list 'mu4e-marks
  '(tag
     :char       "g"
     :prompt     "gtag"
     :ask-target (lambda () (read-string "What tag do you want to add?"))
     :action      (lambda (docid msg target)
		    (mu4e-action-retag-message msg (concat "+" target)))))
@end lisp

As another example, suppose we would like to ``archive and mark read''
a message (GMail-style), then we can run the following code (after
loading @t{mu4e}):

@lisp
(add-to-list 'mu4e-marks
  '(archive
     :char       "A"
     :prompt     "Archive"
     :show-target (lambda (target) "archive")
     :action      (lambda (docid msg target)
		    ;; must come before proc-move since retag runs
		    ;; 'sed' on the file
		    (mu4e-action-retag-message msg "-\\Inbox")
		    (mu4e~proc-move docid nil "+S-u-N"))))
@end lisp

Adding to @code{mu4e-marks} list allows to use the mark in bulk operations
(for example when tagging a whole thread), but does not bind the mark
to a key to use at the top-level. This must be done separately. In our
example:

@lisp
(mu4e~headers-defun-mark-for tag)
(mu4e~headers-defun-mark-for archive)
(define-key mu4e-headers-mode-map (kbd "g") 'mu4e-headers-mark-for-tag)
(define-key mu4e-headers-mode-map (kbd "A") 'mu4e-headers-mark-for-archive)
@end lisp

@node Contexts
@chapter Contexts

@menu
* What are contexts::Defining the concept
* Context policies::How to determine the current context
* Contexts and special folders::Using context variables to determine them
* Contexts example::How to define contexts
* Some context tricks::Other thing to do with contexts
@end menu

It can be useful to switch between different sets of settings in
@t{mu4e}; a typical example is the case where you have different e-mail
accounts for private and work email, each with their own values for
folders, e-mail addresses, mailservers and so on.

The @code{mu4e-context} system is a @t{mu4e}-specific mechanism to allow
for that; users can define different @i{contexts} corresponding with
groups of setting and either manually switch between them, or let
@t{mu4e} determine the right context based on some user-provided
function.

Note that there are a number of existing ways to switch accounts in
@t{mu4e}, for example using the method described in the @ref{Tips and
Tricks} section of this manual. Those still work --- but the new mechanism
has the benefit of being a core part of @code{mu4e}, thus allowing for
deeper integration.

@node What are contexts
@section What are contexts

Let's see what's contained in a context. Most of it is optional.

A @code{mu4e-context} is Lisp object with the following members:
@itemize
@item @t{name}: the name of the context, e.g. @t{work} or @t{private}
@item @t{vars}:
an association-list (alist) of variable settings for this account.
@item @t{enter-func}:
an (optional) function that takes no parameter and is invoked when entering
the context. You can use this for extra setup etc.
@item @t{leave-func}:
an (optional) function that takes no parameter and is invoked when leaving
the context. You can use this for clearing things up.
@item @t{match-func}:
an (optional) function that takes an @t{MSG} message plist as argument,
and returns non-@t{nil} if this context matches the situation. @t{mu4e}
uses the first context that matches, in a couple of situations:
@itemize
@item when starting @t{mu4e} to determine the
starting context; in this case, @t{MSG} is nil. You can use e.g. the
host you're running or the time of day to determine which context
matches.
@item before replying to or forwarding a
message with the given message plist as parameter, or @t{nil} when
composing a brand new message. The function should return @t{t} when
this context is the right one for this message, or @t{nil} otherwise.
@item when determining the target folders for deleting, refiling etc;
see @ref{Contexts and special folders}.
@end itemize
@end itemize

@t{mu4e} uses a variable @code{mu4e-contexts}, which is a list of such
objects.

@node Context policies
@section Context policies

When you have defined contexts and you start @t{mu4e} it decides which
context to use based on the variable @code{mu4e-context-policy};
similarly, when you compose a new message, the context is determined
using @code{mu4e-compose-context-policy}.

For both of these, you can choose one of the following policies:
@itemize
@item a symbol @code{always-ask}: unconditionally ask the user what context to pick.
@end itemize

The other choices @b{only apply if none of the contexts match} (i.e.,
none of the contexts' match-functions returns @code{t}). We have the
following options:

@itemize
@item a symbol @code{ask}: ask the user if @t{mu4e} can't figure
things out the context by itself (through the match-function). This is a
good policy if there are no match functions, or if the match functions
don't cover all cases.
@item a symbol @code{ask-if-none}: if there's already a context, don't change it; otherwise,
ask the user.
@item a symbol @code{pick-first}: pick the first (default) context. This is a good choice if
you want to specify context for special case, and fall back to the first
one if none match.
@item @code{nil}: don't change the context; this is useful if you don't change
contexts very often, and e.g. manually changes contexts with @kbd{M-x
mu4e-context-switch}.
@end itemize

@node Contexts and special folders
@section Contexts and special folders

As we discussed in @ref{Folders} and @ref{Dynamic folders}, @t{mu4e}
recognizes a number of special folders: @code{mu4e-sent-folder},
@code{mu4e-drafts-folder}, @code{mu4e-trash-folder} and
@code{mu4e-refile-folder}.

When you have a headers-buffer with messages that belong to different
contexts (say, a few different accounts), it is desirable for each of
them to use the specific folders for their own context --- so, for
instance, if you trash a message, it needs to go to the trash-folder for
the account it belongs to, which is not necessarily the current context.

To make this easy to do, whenever @t{mu4e} needs to know the value for
such a special folder for a given message, it tries to determine the
appropriate context using @code{mu4e-context-determine} (and policy
@t{nil}; see @ref{Context policies}). If it finds a matching context, it
let-binds the @code{vars} for that account, and then determines the
value for the folder. It does not, however, call the @code{enter-func}
or @code{leave-func}, since we are not really switching contexts.

In practice, this means that as long as each of the accounts has a good
@t{match-func}, all message operations automatically find the
appropriate folders.

@node Contexts example
@section Example

Let's explain how contexts work by looking at an example. We define two
contexts, `Private' and `Work' for a fictional user @emph{Alice
Derleth}.

Note that in this case, we automatically switch to the first context
when starting; see the discussion in the previous section.

@lisp

 (setq mu4e-contexts
    `( ,(make-mu4e-context
	  :name "Private"
	  :enter-func (lambda () (mu4e-message "Entering Private context"))
          :leave-func (lambda () (mu4e-message "Leaving Private context"))
	  ;; we match based on the contact-fields of the message
	  :match-func (lambda (msg)
			(when msg 
			  (mu4e-message-contact-field-matches msg 
			    :to "aliced@@home.example.com")))
	  :vars '( ( user-mail-address	    . "aliced@@home.example.com"  )
		   ( user-full-name	    . "Alice Derleth" )
		   ( mu4e-compose-signature .
		     (concat
		       "Alice Derleth\n"
		       "Lauttasaari, Finland\n"))))
       ,(make-mu4e-context
	  :name "Work"
	  :enter-func (lambda () (mu4e-message "Switch to the Work context"))
	  ;; no leave-func
	  ;; we match based on the maildir of the message
	  ;; this matches maildir /Arkham and its sub-directories
	  :match-func (lambda (msg)
			(when msg
			  (string-match-p "^/Arkham" (mu4e-message-field msg :maildir))))
	  :vars '( ( user-mail-address	     . "aderleth@@miskatonic.example.com" )
		   ( user-full-name	     . "Alice Derleth" )
		   ( mu4e-compose-signature  .
		     (concat
		       "Prof. Alice Derleth\n"
		       "Miskatonic University, Dept. of Occult Sciences\n"))))

       ,(make-mu4e-context
	  :name "Cycling"
	  :enter-func (lambda () (mu4e-message "Switch to the Cycling context"))
	  ;; no leave-func
	  ;; we match based on the maildir of the message; assume all
	  ;; cycling-related messages go into the /cycling maildir
	  :match-func (lambda (msg)
			(when msg
			  (string= (mu4e-message-field msg :maildir) "/cycling")))
	  :vars '( ( user-mail-address	     . "aderleth@@example.com" )
		   ( user-full-name	     . "AliceD" )
		   ( mu4e-compose-signature  . nil)))))

  ;; set `mu4e-context-policy` and `mu4e-compose-policy` to tweak when mu4e should
  ;; guess or ask the correct context, e.g.

  ;; start with the first (default) context; 
  ;; default is to ask-if-none (ask when there's no context yet, and none match)
  ;; (setq mu4e-context-policy 'pick-first)

  ;; compose with the current context is no context matches;
  ;; default is to ask 
  ;; (setq mu4e-compose-context-policy nil)
@end lisp

A couple of notes about this example:
@itemize
@item You can manually switch the context use @code{M-x mu4e-context-switch},
by default bound to @kbd{;} in headers, view and main mode.
The current context appears in the mode-line.
@item Normally, @code{M-x mu4e-context-switch} does not call the enter or 
leave functions if the 'new' context is the same as the old one.
However, with a prefix-argument (@kbd{C-u}), you can force @t{mu4e} to
invoke those function even in that case.
@item The function @code{mu4e-context-current} returns the current-context; 
the current context is also visible in the mode-line when in
headers, view or main mode.
@item You can set any kind of variable; including settings for mail servers etc. 
However, settings such as @code{mu4e-maildir} and @code{mu4e-mu-home} are
not changeable after they have been set without quitting @t{mu4e} first.
@item @code{leave-func} (if defined) for the context we are leaving, is invoked 
before the @code{enter-func} (if defined) of the
context we are entering.
@item @code{enter-func} (if defined) is invoked before setting the variables.
@item @code{match-func} (if defined) is invoked just before @code{mu4e-compose-pre-hook}.
@item See the variables @code{mu4e-context-policy} and
@code{mu4e-compose-context-policy} to tweak what @t{mu4e} should do when 
no context matches (or if you always want to be asked).
@item Finally, be careful to get the quotations right --- backticks, single quotes 
and commas and note the '.' between variable name and its value.
@end itemize

@node Some context tricks
@section Some context tricks

It is possible to automatically fill @code{mu4e-user-address-list} by
concatenating the @code{user-mail-address} fields of all contexts:

@lisp
  ;; This sets `mu4e-user-mail-address-list' to the concatenation of all
  ;; `user-mail-address' values for all contexts. If you have other mail
  ;; addresses as well, you'll need to add those manually.
  (setq mu4e-user-mail-address-list
    (delq nil
      (mapcar (lambda (context)
		(when (mu4e-context-vars context)
		  (cdr (assq 'user-mail-address (mu4e-context-vars context)))))
	mu4e-contexts)))
@end lisp


@node Dynamic folders
@chapter Dynamic folders

In @ref{Folders}, we explained how you can set up @t{mu4e}'s special
folders:
@lisp
(setq
  mu4e-sent-folder   "/sent"	   ;; sent messages
  mu4e-drafts-folder "/drafts"	   ;; unfinished messages
  mu4e-trash-folder  "/trash"	   ;; trashed messages
  mu4e-refile-folder "/archive")   ;; saved messages01
@end lisp

In some cases, having such static folders may not suffice --- perhaps you want
to change the folders depending on the context. For example, the folder for
refiling could vary, based on the sender of the message.

To make this possible, instead of setting the standard folders to a string,
you can set them to be a @emph{function} that takes a message as its
parameter, and returns the desired folder name. This chapter shows you how to
do that. For a more general discussion of how to extend @t{mu4e} and writing
your own functions, see @ref{Extending mu4e}.

If you use @t{mu4e-context}, see @ref{Contexts and special folders} for
what that means for these special folders.

@menu
* Smart refiling:: Automatically choose the target folder
* Other dynamic folders:: Flexible folders for sent, trash, drafts
@end menu


@node Smart refiling
@section Smart refiling

When refiling messages, perhaps to archive them, it can be useful to have
different target folders for different messages, based on some property of
those message --- smart refiling.

To accomplish this, we can set the refiling folder (@code{mu4e-refile-folder})
to a function that returns the actual refiling folder for the particular
message. An example should clarify this:

@lisp
(setq mu4e-refile-folder
  (lambda (msg)
    (cond
      ;; messages to the mu mailing list go to the /mu folder
      ((mu4e-message-contact-field-matches msg :to
	 "mu-discuss@@googlegroups.com")
	"/mu")
      ;; messages sent directly to me go to /archive
      ;; also `mu4e-user-mail-address-p' can be used
      ((mu4e-message-contact-field-matches msg :to "me@@example.com")
	"/private")
      ;; messages with football or soccer in the subject go to /football
      ((string-match "football\\|soccer"
	 (mu4e-message-field msg :subject))
	"/football")
      ;; messages sent by me go to the sent folder
      ((find-if
	 (lambda (addr)
	   (mu4e-message-contact-field-matches msg :from addr))
	 mu4e-user-mail-address-list)
	mu4e-sent-folder)
      ;; everything else goes to /archive
      ;; important to have a catch-all at the end!
      (t  "/archive"))))
@end lisp

@noindent
This can be very powerful; you can select some messages in the headers view,
then press @key{r}, and have them all marked for refiling to their particular
folders.

Some notes:
@itemize
@item We set @code{mu4e-refile-folder} to an anonymous (@t{lambda}) function. This
function takes one argument, a message plist@footnote{a property list
describing a message}. The plist corresponds to the message at point. See
@ref{Message functions} for a discussion on how to deal with them.
@item In our function, we use a @t{cond} control structure; the function
returns the first of the clauses that matches. It's important to make the last
clause a catch-all, so we always return @emph{some} folder.
@item We use
the convenience function @code{mu4e-message-contact-field-matches},
which evaluates to @code{t} if any of the names or e-mail addresses in a
contact field (in this case, the @t{To:}-field) matches the regular
expression. With @t{mu4e} version 0.9.16 or newer, the contact field can
in fact be a list instead of a single value, such as @code{'(:to :cc)'}.
@end itemize

@node Other dynamic folders
@section Other dynamic folders

Using the same mechanism, you can create dynamic sent-, trash-, and
drafts-folders. The message-parameter you receive for the sent and drafts
folder is the @emph{original} message, that is, the message you reply to, or
forward, or edit. If there is no such message (for example when composing a
brand new message) the message parameter is @t{nil}.

Let's look at an example. Suppose you want a different trash folder for
work-email. You can achieve this with something like:

@lisp
(setq mu4e-trash-folder
(lambda (msg)
;; the 'and msg' is to handle the case where msg is nil
(if (and msg
(mu4e-message-contact-field-matches msg :to "me@@work.example.com"))
"/trash-work"
"/trash")))
@end lisp

@noindent
Good to remember:
@itemize
@item The @var{msg} parameter you receive in the function refers to the
@emph{original message}, that is, the message being replied to or
forwarded. When re-editing a message, it refers to the message being
edited. When you compose a totally new message, the @var{msg} parameter is
@code{nil}.
@item When re-editing messages, the value of @code{mu4e-drafts-folder} is ignored.
@end itemize


@node Actions
@chapter Actions

@t{mu4e} lets you define custom actions for messages in the @ref{Headers view}
and for both messages and attachments in the @ref{Message view}. Custom
actions allow you to easily extend @t{mu4e} for specific needs --- for example,
marking messages as spam in a spam filter or applying an attachment with a
source code patch.

You can invoke the actions with key @key{a} for actions on messages, and key
@key{A} for actions on attachments.

For general information extending @t{mu4e} and writing your own functions, see
@ref{Extending mu4e}.

@menu
* Defining actions::How to create an action
* Headers view actions::Doing things with message headers
* Message view actions::Doing things with messages
* Attachment actions::Doing things with attachments
* Example actions::Some more examples
@end menu

@node Defining actions
@section Defining actions

Defining a new custom action comes down to writing an elisp-function to do the
work. Functions that operate on messages receive a @var{msg} parameter, which
corresponds to the message at point. Something like:
@lisp
  (defun my-action-func (msg)
  "Describe my message function."
  ;; do stuff
  )
@end lisp

@noindent
Functions that operate on attachments receive a @var{msg} parameter, which
corresponds to the message at point, and an @var{attachment-num}, which is the
number of the attachment as seen in the message view. An attachment function
looks like:
@lisp
  (defun my-attachment-action-func (msg attachment-num)
  "Describe my attachment function."
  ;; do stuff
  )
@end lisp

@noindent
After you have defined your function, you can add it to the list of
actions@footnote{Instead of defining the functions separately, you can
obviously also add a @code{lambda}-function directly to the list; however,
separate functions are easier to change}, either @code{mu4e-headers-actions},
@code{mu4e-view-actions} or @code{mu4e-view-attachment-actions}.  The
format@footnote{Note, the format of the actions has changed since version
0.9.8.4, and you must change your configuration to use the new format;
@t{mu4e} warns you when you are using the old format.} of each action is a
cons-cell, @code{(DESCRIPTION . VALUE)}; see below for some examples. If your
shortcut is not also the first character of the description, simply prefix the
description with that character.

Let's look at some examples.

@node Headers view actions
@section Headers view actions

Suppose we want to inspect the number of recipients for a message in the
@ref{Headers view}. We add the following to our configuration:

@lisp
(defun show-number-of-recipients (msg)
  "Display the number of recipients for the message at point."
  (message "Number of recipients: %d"
    (+ (length (mu4e-message-field msg :to))
      (length (mu4e-message-field msg :cc)))))

;; define 'N' (the first letter of the description) as the shortcut
;; the 't' argument to add-to-list puts it at the end of the list
(add-to-list 'mu4e-headers-actions
  '("Number of recipients" . show-number-of-recipients) t)
@end lisp

After evaluating this, @kbd{a N} in the headers view shows the number of
recipients for the message at point.

@node Message view actions
@section Message view actions

As another example, suppose we would like to search for messages by the sender
of the message at point:

@lisp
(defun search-for-sender (msg)
  "Search for messages sent by the sender of the message at point."
  (mu4e-headers-search
    (concat "from:" (cdar (mu4e-message-field msg :from)))))

;; define 'x' as the shortcut
(add-to-list 'mu4e-view-actions
  '("xsearch for sender" . search-for-sender) t)
@end lisp

@indent
If you wonder why we use @code{cdar}, remember that the @t{From:}-field is a
list of @code{(NAME . EMAIL)} cells; thus, @code{cdar} gets us the e-mail
address of the first in the list. @t{From:}-fields rarely contain multiple
cells.

@node Attachment actions
@section Attachment actions

Finally, let's define an attachment action. As mentioned, attachment-action
functions receive @emph{2} arguments, the message and the attachment number to
use.

The following example action counts the number of lines in an attachment, and
defines @key{n} as its shortcut key (the @key{n} is prefixed to the
description).

@lisp
(defun count-lines-in-attachment (msg attachnum)
  "Count the number of lines in an attachment."
  (mu4e-view-pipe-attachment msg attachnum "wc -l"))

;; defining 'n' as the shortcut
(add-to-list 'mu4e-view-attachment-actions
  '("ncount lines" . count-lines-in-attachment) t)
@end lisp

@node Example actions
@section Example actions

@t{mu4e} includes a number of example actions in the file
@file{mu4e-actions.el} in the source distribution (see @kbd{C-h f
mu4e-action-TAB}). For example, for viewing messages in an external web
browser, or listening to a message's body-text using text-to-speech.

@node Extending mu4e
@chapter Extending mu4e

@t{mu4e} is designed to be easily extendible --- that is, write your own
emacs-lisp to make @t{mu4e} behave exactly as you want. Here, we provide some
guidelines for doing so.

@menu
* Extension points::Where to hook into @t{mu4e}
* Available functions::General helper functions
* Message functions::Working with messages
* Contact functions::Working with contacts
* Utility functions::Miscellaneous helpers
@end menu

@node Extension points
@section Extension points

There are a number of places where @t{mu4e} lets you plug in your own
functions:
@itemize
@item Custom functions for message headers in the message-view and
headers-view --- see @ref{HV Custom headers}, @ref{MSGV Custom headers}
@item Using message-specific folders for drafts, trash, sent messages and
refiling, based on a function --- see @ref{Dynamic folders}
@item Using an attachment-specific download-directory --- see the
variable @code{mu4e-attachment-dir}.
@item Apply a function to a message in the headers view -
see @ref{Headers view actions}
@item Apply a function to a message in the message view --- see @ref{Message view actions}
@item Add a new kind of mark for use in the headers view
- see @ref{Adding a new kind of mark}
@item Apply a function to an attachment --- see @ref{Attachment actions}
@item Custom function to mark certain messages --- see @ref{Custom mark functions}
@item Using various @emph{mode}-hooks, @code{mu4e-compose-pre-hook} (see
@ref{Compose hooks}), @code{mu4e-index-updated-hook} (see @ref{FAQ})
@end itemize

@noindent
You can also write your own functions without using the above. If you
want to do so, key useful functions are @code{mu4e-message-at-point}
(see below), @code{mu4e-headers-for-each} (to iterate over all
headers, see its docstring) and @code{mu4e-view-for-each-part} (to
iterate over all parts/attachments, see its docstring). There is also
@code{mu4e-view-for-each-uri} to iterate of all the URIs in the
current message.

Another useful function is
@code{mu4e-headers-find-if} which searches for a message matching a
certain pattern; again, see its docstring.

@node Available functions
@section Available functions

The whole of @t{mu4e} consists of hundreds of elisp functions. However, the
majority of those are for @emph{internal} use only; you can recognize them
easily, because they all start with @code{mu4e~}. These functions make all
kinds of assumptions, and they are subject to change, and should therefore
@emph{not} be used. The same is true for @emph{variables} that start with
@code{mu4e~}; don't touch them.  Let me repeat that:
@verbatim
Do not use mu4e~... functions or variables!
@end verbatim

@noindent
In addition, you should use functions in the right context; functions
that start with @t{mu4e-view-} are only applicable to the message view,
while functions starting with @t{mu4e-headers-} are only applicable to
the headers view. Functions without such prefixes are applicable
everywhere.

@node Message functions
@section Message functions

Many functions in @t{mu4e} deal with message plists (property
lists). They contain information about messages, such as sender and
recipient, subject, date and so on. To deal with these plists, there are
a number of @code{mu4e-message-} functions (in @file{mu4e-message.el}),
such as @code{mu4e-message-field} and @code{mu4e-message-at-point}, and
a shortcut to combine the two, @code{mu4e-message-field-at-point}.

For example, to get the subject of the message at point, in either the headers
view or the message view, you could write:
@lisp
(mu4e-message-field (mu4e-message-at-point) :subject)
@end lisp
@noindent
Note that:
@itemize
@item The contact fields (To, From, Cc, Bcc) are lists of cons-pairs
@code{(name . email)}; @code{name} may be @code{nil}. So, for example:
@lisp
  (mu4e-message-field some-msg :to)
  ;; => (("Jack" . "jack@@example.com") (nil . "foo@@example.com"))
@end lisp

If you are only looking for a match in this list (e.g., ``Is Jack one of the
recipients of the message?''), there is a convenience function
@code{mu4e-message-contact-field-matches} to make this easy.
@item The message body is only available in the message view, not in the
headers view.
@end itemize

Note that in headers-mode, you only have access to a reduced message
plist, without the information about the message-body or mime-parts;
@t{mu4e} does this for performance reasons. And even in view-mode, you
do not have access to arbitrary message-headers.

However, it is possible to get the information indirectly, using the
raw-message and some third-party tool like @t{procmail}'s @t{formail}:

@lisp
(defun my-mu4e-any-message-field-at-point (hdr)
  "Quick & dirty way to get an arbitrary header HDR at
point. Requires the 'formail' tool from procmail."
  (replace-regexp-in-string "\n$" ""
    (shell-command-to-string
      (concat "formail -x " hdr " -c < "
	(shell-quote-argument (mu4e-message-field-at-point :path))))))
@end lisp

@subsection Rewriting the message body

Message body rewriting allows you to modify the message text that is
presented in the message view. This can be useful if the message needs
special processing, for instance for special filling or cleaning up
encoding artifacts (this is what @t{mu4e} uses this for internally).

To enable this, you can append your rewrite-function to
@code{mu4e-message-body-rewrite-functions}; your function is expected to
take two parameters @code{MSG} and @code{TXT}, which are the
message-plist and the body-text, which could be the result of earlier
transformations, including html->text conversion as per
@code{mu4e-html2-text-command}. The function is expected to return the
transformed text.

As a fairly useless example, suppose we insist on reading @t{mu4e} as
@t{MU4E}:
@lisp
(defun mu4e-to-MU4E-rewrite (msg txt)
  (replace-regexp-in-string "mu4e" "MU4E" txt))

(add-to-list 'mu4e-message-body-rewrite-functions 'mu4e-to-MU4E-rewrite t)
@end lisp


@node Contact functions
@section Contact functions

It can sometimes be useful to rewrite the contact information that
@t{mu4e} provides, for example to convert them to some standardized
format, or to fix spelling errors. And sometimes, you may want to remove
certain contacts altogether.

For this, @t{mu4e} provides @code{mu4e-contact-rewrite-function}, which
passes each contact to a user-provided function, which is expected to
return either the possibly rewritten contact or @code{nil} to remove the
contact from the list --- note that the latter can also be achieved using
@code{mu4e-compose-complete-ignore-address-regexp}.

Each of the contacts are property-lists (`plists'), with properties
@code{:name} (which may be @code{nil}), and @code{:mail}, and a number
of other properties which you should return unchanged.

Let's look at an example:

@lisp
(defun my-rewrite-function (contact)
  (let ((name (or (plist-get contact :name) ""))
	 (mail (plist-get contact :mail)))
    (cond
      ;; jonh smiht --> John Smith
      ((string= "jonh smiht" name) 
	(plist-put contact :name "John C. Smith")
	contact) 
      ;; remove evilspammer from the contacts list
      ((string= "evilspammer@@example.com" mail) nil)
      ;; others stay as the are
      (t contact))))

(setq mu4e-contact-rewrite-function 'my-rewrite-function)
@end lisp

This function is called for each of your contacts.

@node Utility functions
@section Utility functions

@file{mu4e-utils} contains a number of utility functions; we list a few here.
See their docstrings for details:
@itemize
@item @code{mu4e-read-option}: read one option from a list. For example:
@lisp
(mu4e-read-option "Choose an animal: "
'(("Monkey" . monkey) ("Gnu" . gnu) ("xMoose" . moose)))
@end lisp
The user is presented with:
@example
Choose an animal: [M]onkey, [G]nu, [x]Moose
@end example
@item @code{mu4e-ask-maildir}: ask for a maildir; try one of the
shortcuts (@code{mu4e-maildir-shortcuts}), or the full set of available
maildirs.
@item @code{mu4e-running-p}: return @code{t} if the @t{mu4e} process is
running, @code{nil} otherwise.
@item @code{(mu4e-user-mail-address-p addr)}: return @code{t} if @var{addr} is
one of the user's e-mail addresses (as per @code{mu4e-user-mail-address-list}).
@item @code{mu4e-log} logs to the @t{mu4e} debugging log if it is enabled;
see @code{mu4e-toggle-logging}.
@item @code{mu4e-message}, @code{mu4e-warning}, @code{mu4e-error} are the
@t{mu4e} equivalents of the normal elisp @code{message},
@code{user-error}@footnote{@code{user-error} only appears in @command{emacs}
24.2 and later; in older versions it falls back to @code{error}} and
@code{error} functions.
@end itemize


@node Interaction with other tools
@appendix Interaction with other tools

In this chapter, we discuss some ways in which @t{mu4e} can cooperate
with other tools.

@menu
* Emacs default::Making mu4e the default emacs e-mail program
* Org-mode links::Adding mu4e to your organized life
* Org-contacts::Hooking up with org-contacts
* BBDB::Hooking up with the Insidious Big Brother Database
* Sauron::Getting new mail notifications with Sauron
* Speedbar::A special frame with your folders
* Mu-cite:: Fancy citation engine
* Dired:: Attaching files using @t{dired}
@end menu

@node Emacs default
@section Emacs default

@command{emacs} allows you to select an e-mail program as the default
program it uses when you press @key{C-x m} (@code{compose-mail}), call
@code{report-emacs-bug} and so on. If you want to use @t{mu4e} for this,
you can do so by adding the following to your configuration:

@lisp
(setq mail-user-agent 'mu4e-user-agent)
@end lisp

@node Org-mode links
@section Org-mode links

It can be useful to include links to e-mail messages or even search
queries in your org-mode files. @t{mu4e} supports this with the
@t{org-mu4e} module; you can set it up by adding it to your
configuration, which expects org-mode 8.x. or higher@footnote{If you
have an older version, you can try using @t{org-old-mu4e} instead}.


@lisp
(require 'org-mu4e)
@end lisp

@noindent
After this, you can use the normal @t{org-mode} mechanisms to store
links: @kbd{M-x org-store-link} stores a link to a particular message
when you are in @ref{Message view}. When you are in @ref{Headers view},
@kbd{M-x org-store-link} links to the @emph{query} if
@code{org-mu4e-link-query-in-headers-mode} is non-@code{nil}, and to the
particular message otherwise (which is the default).

You can insert this link later with @kbd{M-x org-insert-link}. From
@t{org-mode}, you can go to the query or message the link points to with
either @kbd{M-x org-agenda-open-link} in agenda buffers, or @kbd{M-x
org-open-at-point} elsewhere --- both typically bound to @kbd{C-c C-o}.

You can also directly @emph{capture} such links --- for example, to add
e-mail messages to your todo-list. For that, @t{org-mu4e} has a function
@code{org-mu4e-store-and-capture}. This captures the message-at-point
(or header --- see the discussion on
@code{org-mu4e-link-query-in-headers-mode} above), then calls org-mode's
capture functionality.

You can add some specific capture-template for this: for example, to add
a message to your todo-list, and set a deadline for processing it within
two days, you could add this to @code{org-capture-templates}:

@lisp
  ("P" "process-soon" entry (file+headline "todo.org" "Todo")
  "* TODO %a %?\nDEADLINE: %(org-insert-time-stamp (org-read-date nil t \"+2d\"))")
@end lisp

If you use the functionality a lot, you may want to define key-bindings
for that in headers and view mode:

@lisp
  (define-key mu4e-headers-mode-map (kbd "C-c c") 'org-mu4e-store-and-capture)
  (define-key mu4e-view-mode-map    (kbd "C-c c") 'org-mu4e-store-and-capture)
@end lisp

@node Org-contacts
@section Org-contacts

Note, @t{mu4e} supports built-in address autocompletion; @ref{Address
autocompletion}, and that is the recommended way to do this. However, it
is also possible to manage your addresses with @t{org-mode}, using
@t{org-contacts}@footnote{@url{https://julien.danjou.info/projects/emacs-packages#org-contacts}}.

@t{mu4e-actions} defines a useful action (@ref{Actions}) for adding a contact
based on the @t{From:}-address in the message at point. To enable this, add to
your configuration something like:

@lisp
  (setq mu4e-org-contacts-file  <full-path-to-your-org-contacts-file>)
  (add-to-list 'mu4e-headers-actions
    '("org-contact-add" . mu4e-action-add-org-contact) t)
  (add-to-list 'mu4e-view-actions
    '("org-contact-add" . mu4e-action-add-org-contact) t)
@end lisp

@noindent
After this, you should be able to add contacts using @key{a o} in the headers
view and the message view, using the @t{org-capture} mechanism. Note, the
shortcut character @key{o} is due to the first character of
@t{org-contact-add}.

@node BBDB
@section BBDB

Note, @t{mu4e} supports built-in address autocompletion; @ref{Address
autocompletion}, and that is the recommended way to do this. However, it
is also possible to manage your addresses with the current (2015-06-23)
development release of @t{BBDB}, or releases of @t{BBDB} after
3.1.2.@footnote{@url{http://savannah.nongnu.org/projects/bbdb/}}.

To enable BBDB, add to your @file{~/.emacs} (or its moral equivalent,
such as @file{~/.emacs.d/init.el}) the following @emph{after} the
@code{(require 'mu4e)} line:

@lisp
  ;; Load BBDB (Method 1)
  (require 'bbdb-loaddefs)
  ;; OR (Method 2)
  ;; (require 'bbdb-loaddefs "/path/to/bbdb/lisp/bbdb-loaddefs.el")
  ;; OR (Method 3)
  ;; (autoload 'bbdb-insinuate-mu4e "bbdb-mu4e")
  ;; (bbdb-initialize 'message 'mu4e)

  (setq bbdb-mail-user-agent 'mu4e-user-agent)
  (setq mu4e-view-mode-hook 'bbdb-mua-auto-update visual-line-mode)
  (setq mu4e-compose-complete-addresses nil)
  (setq bbdb-mua-pop-up t)
  (setq bbdb-mua-pop-up-window-size 5)
  (setq mu4e-view-show-addresses t)  
@end lisp

@noindent
After this, you should be able to:
@itemize
@item In mu4e-view mode, add the sender of the email to BBDB with @key{C-u :}
@item Tab-complete addresses from BBDB when composing emails
@item View the BBDB contact while viewing a message
@end itemize

@node Sauron
@section Sauron

The @command{emacs} package @t{sauron}@footnote{Sauron can be found at
@url{https://github.com/djcb/sauron}, or in the Marmalade package repository
at @url{http://http://marmalade-repo.org/}} (by the same author) can be used
to get notifications about new mails. If you run something like the below
script from your @t{crontab} (or have some other way of having it execute
every @emph{n} minutes), you receive notifications in the @t{sauron}-buffer
when new messages arrive.

@verbatim
#!/bin/sh

# the mu binary
MU=mu

# put the path to your Inbox folder here
CHECKDIR="/home/$LOGNAME/Maildir/Inbox"

sauron_msg () {
DBUS_COOKIE="/home/$LOGNAME/.sauron-dbus"
if test "x$DBUS_SESSION_BUS_ADDRESS" = "x"; then
  if test -e $DBUS_COOKIE; then
    export DBUS_SESSION_BUS_ADDRESS="`cat $DBUS_COOKIE`"
  fi
fi
if test -n "x$DBUS_SESSION_BUS_ADDRESS"; then
  dbus-send --session                          \
    --dest="org.gnu.Emacs"                     \
    --type=method_call                         \
      "/org/gnu/Emacs/Sauron"                  \
      "org.gnu.Emacs.Sauron.AddMsgEvent"       \
      string:shell uint32:3 string:"$1"
fi
}

#
# -mmin -5: consider only messages that were created / changed in the
# the last 5 minutes
#
for f in `find $CHECKDIR -mmin -5 -a -type f`; do
  subject=`$MU view $f | grep '^Subject:' | sed 's/^Subject://'`
  sauron_msg "mail: $subject"
done
@end verbatim

@noindent
You might want to put:
@lisp
(setq sauron-dbus-cookie t)
@end lisp
@noindent
in your setup, to allow the script to find the D-Bus session bus, even when
running outside its session.

@node Speedbar
@section Speedbar

@code{speedbar} is an @command{emacs}-extension that shows navigational information for
an @command{emacs} buffer in a separate frame. Using @code{mu4e-speedbar}, @t{mu4e}
lists your bookmarks and maildir folders and allows for one-click access to
them.

@t{mu4e} loads @t{mu4e-speedbar} automatically; all you need to do to activate
it is @kbd{M-x speedbar}. Then, when then switching to the @ref{Main view},
the speedbar-frame is updated with your bookmarks and maildirs. For speed
reasons, the list of maildirs is determined when @t{mu4e} starts; if the list
of maildirs changes while @t{mu4e} is running, you need to restart @t{mu4e} to
have those changes reflected in the speedbar and in other places that use this
list, such as auto-completion when jumping to a maildir.

@code{mu4e-speedbar} was contributed by @emph{Antono Vasiljev}.

@node Mu-cite
@section Mu-cite

@t{mu-cite}@footnote{Note, despite its name, @t{mu-cite} is a project
unconnected to @t{mu}/@t{mu4e}} is a package to control the way message
citations look like (i.e., the message you responded to when you reply to them
or forward them), with its latest version available at
@url{http://www.jpl.org/elips/mu/}.

After installing @t{mu-cite}, you can use something like the following to make
it work with @t{mu4e}:

@lisp
(require 'mu-cite)
(setq mu4e-compose-cite-function 'mu-cite-original)
(setq mu-cite-top-format '("On " date ", " from " wrote:\n\n"))
(setq mu-cite-prefix-format '(" > "))
@end lisp

@node Dired
@section Dired

It is possible to attach files to @t{mu4e} messages using @t{dired}
(@inforef{Dired,,emacs}), using the following steps (based on a post on the
@t{mu-discuss} mailing list by @emph{Stephen Eglen}).

To prepare for this, you need a special version of the
@code{gnus-dired-mail-buffers} function so it understands @t{mu4e} buffers as
well; so put in your configuration:

@lisp
(require 'gnus-dired)
;; make the `gnus-dired-mail-buffers' function also work on
;; message-mode derived modes, such as mu4e-compose-mode
(defun gnus-dired-mail-buffers ()
  "Return a list of active message buffers."
  (let (buffers)
    (save-current-buffer
      (dolist (buffer (buffer-list t))
	(set-buffer buffer)
	(when (and (derived-mode-p 'message-mode)
		(null message-sent-message-via))
	  (push (buffer-name buffer) buffers))))
    (nreverse buffers)))

(setq gnus-dired-mail-mode 'mu4e-user-agent)
(add-hook 'dired-mode-hook 'turn-on-gnus-dired-mode)
@end lisp

Then, mark the file(s) in @t{dired} you would like to attach and press @t{C-c
RET C-a}, and you'll be asked whether to attach them to an existing message,
or create a new one.

@node Example configurations
@appendix Example configurations

In this chapter, we show some example configurations. While it is very useful
to see some working settings, we'd like to warn against blindly copying such
things.

@menu
* Minimal configuration::Simplest configuration to get you going
* Longer configuration::A more extensive setup
* Gmail configuration::GMail-specific setup
* Other settings:CONF Other settings. Some other useful configuration

@end menu

@node Minimal configuration
@section Minimal configuration

An (almost) minimal configuration for @t{mu4e} might look like this --- as you
see, most of it is commented-out.

@lisp
;; example configuration for mu4e

;; make sure mu4e is in your load-path
(require 'mu4e)

;; use mu4e for e-mail in emacs
(setq mail-user-agent 'mu4e-user-agent)

;; Only needed if your maildir is _not_ ~/Maildir
;; Must be a real dir, not a symlink
;;(setq mu4e-maildir "/home/user/Maildir")

;; these must start with a "/", and must exist
;; (i.e.. /home/user/Maildir/sent must exist)
;; you use e.g. 'mu mkdir' to make the Maildirs if they don't
;; already exist

;; below are the defaults; if they do not exist yet, mu4e offers to
;; create them. they can also functions; see their docstrings.
;; (setq mu4e-sent-folder   "/sent")
;; (setq mu4e-drafts-folder "/drafts")
;; (setq mu4e-trash-folder  "/trash")

;; smtp mail setting; these are the same that `gnus' uses.
(setq
   message-send-mail-function   'smtpmail-send-it
   smtpmail-default-smtp-server "smtp.example.com"
   smtpmail-smtp-server         "smtp.example.com"
   smtpmail-local-domain        "example.com")
@end lisp


@node Longer configuration
@section Longer configuration

A somewhat longer configuration, showing some more things that you can
customize.

@lisp
;; example configuration for mu4e
(require 'mu4e)

;; use mu4e for e-mail in emacs
(setq mail-user-agent 'mu4e-user-agent)

;; path to our Maildir directory
(setq mu4e-maildir "/home/user/Maildir")

;; the next are relative to `mu4e-maildir'
;; instead of strings, they can be functions too, see
;; their docstring or the chapter 'Dynamic folders'
(setq mu4e-sent-folder   "/sent"
      mu4e-drafts-folder "/drafts"
      mu4e-trash-folder  "/trash")

;; the maildirs you use frequently; access them with 'j' ('jump')
(setq   mu4e-maildir-shortcuts
    '(("/archive"     . ?a)
      ("/inbox"       . ?i)
      ("/work"        . ?w)
      ("/sent"        . ?s)))

;; a  list of user's e-mail addresses
(setq mu4e-user-mail-address-list '("foo@@bar.example.com" "cuux@@example.com")

;; the headers to show in the headers list -- a pair of a field
;; and its width, with `nil' meaning 'unlimited'
;; (better only use that for the last field.
;; These are the defaults:
(setq mu4e-headers-fields
    '( (:date          .  25)    ;; alternatively, use :human-date
       (:flags         .   6)
       (:from          .  22)
       (:subject       .  nil))) ;; alternatively, use :thread-subject

;; program to get mail; alternatives are 'fetchmail', 'getmail'
;; isync or your own shellscript. called when 'U' is pressed in
;; main view.

;; If you get your mail without an explicit command,
;; use "true" for the command (this is the default)
(setq mu4e-get-mail-command "offlineimap")

;; general emacs mail settings; used when composing e-mail
;; the non-mu4e-* stuff is inherited from emacs/message-mode
(setq mu4e-reply-to-address "foo@@bar.example.com"
      user-mail-address "foo@@bar.example.com"
      user-full-name  "Foo X. Bar")
(setq mu4e-compose-signature
   "Foo X. Bar\nhttp://www.example.com\n")

;; smtp mail setting
(setq
   message-send-mail-function 'smtpmail-send-it
   smtpmail-default-smtp-server "smtp.example.com"
   smtpmail-smtp-server "smtp.example.com"
   smtpmail-local-domain "example.com"

   ;; if you need offline mode, set these -- and create the queue dir
   ;; with 'mu mkdir', i.e.. mu mkdir /home/user/Maildir/queue
   smtpmail-queue-mail  nil
   smtpmail-queue-dir  "/home/user/Maildir/queue/cur")

;; don't keep message buffers around
(setq message-kill-buffer-on-exit t)
@end lisp


@node Gmail configuration
@section Gmail configuration

@emph{Gmail} is a popular e-mail provider; let's see how we can make it work
with @t{mu4e}. Since we are using @abbr{IMAP}, you must enable that in the
Gmail web interface (in the settings, under the ``Forwarding and
POP/IMAP''-tab).

Gmail users may also be interested in @ref{Including related messages,
skipping duplicates}.

@subsection Setting up offlineimap

First of all, we need a program to get the e-mail from Gmail to our local
machine; for this we use @t{offlineimap}; on Debian (and derivatives like
Ubuntu), this is as easy as:

@verbatim
$ sudo apt-get install offlineimap
@end verbatim

while on Fedora (and similar) you need:
@verbatim
$ sudo yum install offlineimap
@end verbatim

Then, we can configure @t{offlineimap} by editing @file{~/.offlineimaprc}:

@verbatim
[general]
accounts = Gmail
maxsyncaccounts = 3

[Account Gmail]
localrepository = Local
remoterepository = Remote

[Repository Local]
type = Maildir
localfolders = ~/Maildir

[Repository Remote]
type = IMAP
remotehost = imap.gmail.com
remoteuser = USERNAME@gmail.com
remotepass = PASSWORD
ssl = yes
maxconnections = 1
@end verbatim

Obviously, you need to replace @t{USERNAME} and @t{PASSWORD} with your actual
Gmail username and password. After this, you should be able to download your
mail:

@verbatim
$ offlineimap
 OfflineIMAP 6.3.4
Copyright 2002-2011 John Goerzen & contributors.
Licensed under the GNU GPL v2+ (v2 or any later version).

Account sync Gmail:
 ***** Processing account Gmail
 Copying folder structure from IMAP to Maildir
 Establishing connection to imap.gmail.com:993.
Folder sync [Gmail]:
 Syncing INBOX: IMAP -> Maildir
 Syncing [Gmail]/All Mail: IMAP -> Maildir
 Syncing [Gmail]/Drafts: IMAP -> Maildir
 Syncing [Gmail]/Sent Mail: IMAP -> Maildir
 Syncing [Gmail]/Spam: IMAP -> Maildir
 Syncing [Gmail]/Starred: IMAP -> Maildir
 Syncing [Gmail]/Trash: IMAP -> Maildir
Account sync Gmail:
 ***** Finished processing account Gmail
@end verbatim

We can now run @command{mu} to make sure things work:

@verbatim
$ mu index
mu: indexing messages under /home/foo/Maildir [/home/foo/.mu/xapian]
| processing mail; processed: 520; updated/new: 520, cleaned-up: 0
mu: elapsed: 3 second(s), ~ 173 msg/s
mu: cleaning up messages [/home/foo/.mu/xapian]
/ processing mail; processed: 520; updated/new: 0, cleaned-up: 0
mu: elapsed: 0 second(s)
@end verbatim

We can run both the @t{offlineimap} and the @t{mu index} from within
@t{mu4e}, but running it from the command line makes it a bit easier to
troubleshoot as we are setting things up.

Note: when using encryption, you probably do @emph{not} want to
synchronize your Drafts-folder, since it contains the unencrypted
messages. You can use OfflineIMAP's @t{folderfilter} for that.

@subsection Settings

Next step: let's make a @t{mu4e} configuration for this:

@lisp
(require 'mu4e)

;; use mu4e for e-mail in emacs
(setq mail-user-agent 'mu4e-user-agent)

;; default
;; (setq mu4e-maildir "~/Maildir")

(setq mu4e-drafts-folder "/[Gmail].Drafts")
(setq mu4e-sent-folder   "/[Gmail].Sent Mail")
(setq mu4e-trash-folder  "/[Gmail].Trash")

;; don't save message to Sent Messages, Gmail/IMAP takes care of this
(setq mu4e-sent-messages-behavior 'delete)

;; (See the documentation for `mu4e-sent-messages-behavior' if you have
;; additional non-Gmail addresses and want assign them different
;; behavior.)

;; setup some handy shortcuts
;; you can quickly switch to your Inbox -- press ``ji''
;; then, when you want archive some messages, move them to
;; the 'All Mail' folder by pressing ``ma''.

(setq mu4e-maildir-shortcuts
    '( ("/INBOX"               . ?i)
       ("/[Gmail].Sent Mail"   . ?s)
       ("/[Gmail].Trash"       . ?t)
       ("/[Gmail].All Mail"    . ?a)))

;; allow for updating mail using 'U' in the main view:
(setq mu4e-get-mail-command "offlineimap")

;; something about ourselves
(setq
   user-mail-address "USERNAME@@gmail.com"
   user-full-name  "Foo X. Bar"
   mu4e-compose-signature
    (concat
      "Foo X. Bar\n"
      "http://www.example.com\n"))

;; sending mail -- replace USERNAME with your gmail username
;; also, make sure the gnutls command line utils are installed
;; package 'gnutls-bin' in Debian/Ubuntu

(require 'smtpmail)
(setq message-send-mail-function 'smtpmail-send-it
   starttls-use-gnutls t
   smtpmail-starttls-credentials '(("smtp.gmail.com" 587 nil nil))
   smtpmail-auth-credentials
     '(("smtp.gmail.com" 587 "USERNAME@@gmail.com" nil))
   smtpmail-default-smtp-server "smtp.gmail.com"
   smtpmail-smtp-server "smtp.gmail.com"
   smtpmail-smtp-service 587)

;; alternatively, for emacs-24 you can use:
;;(setq message-send-mail-function 'smtpmail-send-it
;;     smtpmail-stream-type 'starttls
;;     smtpmail-default-smtp-server "smtp.gmail.com"
;;     smtpmail-smtp-server "smtp.gmail.com"
;;     smtpmail-smtp-service 587)

;; don't keep message buffers around
(setq message-kill-buffer-on-exit t)
@end lisp

And that's it --- put the above in your @file{~/.emacs}, change @t{USERNAME}
etc. to your own, and restart @command{emacs}, and run @kbd{M-x mu4e}.

@node CONF Other settings
@section Other settings

Finally, here are some more settings that are useful, but not enabled by
default for various reasons.

@lisp
;; use 'fancy' non-ascii characters in various places in mu4e
(setq mu4e-use-fancy-chars t)

;; save attachment to my desktop (this can also be a function)
(setq mu4e-attachment-dir "~/Desktop")

;; attempt to show images when viewing messages
(setq mu4e-view-show-images t)
@end lisp

@node FAQ
@appendix FAQ --- Frequently Asked Questions

In this chapter we list a number of actual and anticipated questions and their
answers.

@menu
* General::General questions and answers about @t{mu4e}
* Retrieving mail::Getting mail and indexing
* Reading messages::Dealing with incoming messages
* Writing messages::Dealing with outgoing messages
* Known issues::Limitations we know about
@end menu

@node General
@section General

@enumerate
@item @emph{Does @t{mu4e} provide context-sensitive help information?} Yes --- pressing @key{H}
should take you to the right section in this manual.
@item @emph{How can I quickly delete/move/trash a lot of messages?} You can
select ('mark' in @command{emacs}-speak) the messages like you would select
text in a buffer; the actions you then take (e.g., @key{DEL} for delete,
@key{m} for move and @key{t} for trash) apply to all selected messages. You
can also use functions like @code{mu4e-headers-mark-thread} (@key{T}),
@code{mu4e-headers-mark-subthread} (@key{t}) to mark whole threads at the same
time, and @code{mu4e-headers-mark-pattern} (@key{%}) to mark all messages
matching a certain regular expression.
@item @emph{@t{mu4e} seems to return a subset of all matches --- how can I
get them all?} For speed reasons, @t{mu4e} returns only up to the value
of the variable @code{mu4e-search-result-limit} (default: 500)
matches. To show @emph{all}, use @kbd{M-x
mu4e-headers-toggle-full-search} (@key{Q}), or customize the variable
@code{mu4e-headers-full-search}. This applies to all search commands.
@item @emph{Can I automatically apply the marks on messages when
leaving the headers buffer?} Yes you can --- see the documentation for the
variable @t{mu4e-headers-leave-behavior}.
@item @emph{How can I set @t{mu4e} as the default e-mail client in @command{emacs}?}
See @ref{Emacs default}.
@item @emph{Can @t{mu4e} use some fancy Unicode characters instead of these
boring plain-ASCII ones?} Glad you asked! Yes, if you set
@code{mu4e-use-fancy-chars} to @t{t}, @t{mu4e} uses such fancy
characters in a number of places. Since not all fonts include all
characters, you may want to install the @t{unifont} and/or @t{symbola}
fonts on your system.
@item @emph{Can I start @t{mu4e} in the background?} Yes --- if you provide a
prefix-argument (@key{C-u}), @t{mu4e} starts, but does not show the
main-window.
@item @emph{Does @t{mu4e} support searching for CJK (Chinese-Japanese-Korean) characters?}
Yes, if you have @t{Xapian} 1.2.8 or newer, and set the environment
variable @t{XAPIAN_CJK_NGRAM} to non-empty before indexing, both when
using @t{mu} from the command-line and from @t{mu4e}.
@item @emph{How can I customize the function to select a folder?}
The @t{mu4e-completing-read-function} variable can be customized to select a
folder in any way. The variable can be set to a function that receives
five arguments, following @t{completing-read}. The default value is
@code{ido-completing-read}; to use emacs's default behavior, set the
variable to @code{completing-read}. Helm users can use the same value,
and by enabling @code{helm-mode} use helm-style completion.
@item @emph{I have a lot of Maildir folders, so regenerating them each time makes
things slow. What can I do?}
Set @code{mu4e-cache-maildir-list} to @code{t} (but make sure to read
its docstring).
@item @emph{How can I hide certain message from the search results?}
See the variable @code{mu4e-headers-hide-predicate}.
@item @emph{I'm getting an error 'Variable binding depth exceeds max-specpdl-size'
when using mu4e -- what can I do about it?}  The error occurs because
@t{mu4e} is binding more variables than @t{emacs} allows for, by
default. You can avoid this by setting a higher value, e.g. by adding the
following to your configuration:
@lisp
(setq max-specpdl-size 5000)
@end lisp
@end enumerate

@node Retrieving mail
@section Retrieving mail

@enumerate
@item @emph{How can I get notifications when receiving mail?} There is
@code{mu4e-index-updated-hook}, which gets triggered when the indexing
process triggered sees an update (not just new mail though). To use this
hook, put something like the following in your setup (assuming you have
@t{aplay} and some soundfile, change as needed):
@lisp
(add-hook 'mu4e-index-updated-hook
  (defun new-mail-sound ()
    (shell-command "aplay ~/Sounds/boing.wav&")))
@end lisp
@item @emph{It seems my headers-buffer is automatically updated when new
  messages are found during the indexing process --- can I disable this
  somehow?} Yes --- set @code{mu4e-headers-auto-update} to @code{nil}.
@item @emph{I don't use @t{offlineimap}, @t{fetchmail} etc., I get my mail
through my own mailserver. What should I use for
@code{mu4e-get-mail-command}}? Use the literal string @t{"true"} (or
don't do anything, it's the default) which then uses @t{/bin/true} (a
command that does nothing and always succeeds). This makes getting mail
a no-op, but the messages are still re-indexed.
@item @emph{How can I re-index my messages without getting new mail?}
Use @kbd{M-x mu4e-update-index}
@item @emph{When I try to run @t{mu index} while @t{mu4e} is running I get
errors like:}
@verbatim
mu: mu_store_new_writable: xapian error
  'Unable to get write lock on ~/.mu/xapian: already locked
@end verbatim
@emph{What to do about this?}  You get this error because the underlying
Xapian database is locked by some other process; it can be opened only once in
read-write mode. There is not much @t{mu4e} can do about this, but if is
another @command{mu} instance that is holding the lock, you can ask it to
(gracefully) terminate:
@verbatim
   pkill -2 -u $UID mu # send SIGINT
   sleep 1
   mu index
@end verbatim
@t{mu4e} automatically restarts @t{mu} when it needs it. In practice, this
seems to work quite well.
@item @emph{I don't like the @t{Indexing...} messages that the indexing process
gives me. Can I turn them off?}. Yes: set the variable
@code{mu4e-hide-index-messages} to non-@t{nil}.
@item @emph{Some IMAP-synchronization programs such as @t{mbsync} (but not
@t{offlineimap}) don't like it when message files do not change their names
when they are moved to different folders. Can @t{mu4e} somehow accommodate
this?} Yes --- you can set the variable @code{mu4e-change-filenames-when-moving}
to non-@t{nil}.
@item @emph{@command{offlineimap} uses IMAP's UTF-7 for encoding
non-ascii folder names, while @t{mu} expects UTF-8 (so, e.g. @t{/まりも
えお}@footnote{some Japanese characters} becomes
@t{/&MH4wijCCMEgwSg-}). How can I make @t{mu4e} display such folders
correctly?} This is best solved by telling @command{offlineimap} to use
UTF-8 instead --- see
@url{https://github.com/djcb/mu/issues/68#issuecomment-8598652}.
@end enumerate

@node Reading messages
@section Reading messages

@enumerate
@item @emph{How can I view attached images in my message view buffers?} See
@ref{Viewing images inline}.
@item @emph{How can I word-wrap long lines in when viewing a
message?} You can toggle between wrapped and non-wrapped states using
@key{w}. If you want to do this automatically, invoke @code{visual-line-mode} in
your @code{mu4e-view-mode-hook}.
@item @emph{How can I perform custom actions on messages and attachments?} See
@ref{Actions}.
@item @emph{Does @t{mu4e} support crypto (i.e., decrypting messages and
verifying signatures)?}  Yes --- if @t{mu} was built with @t{GMime} 2.6
or later, it is possible to do both (note, only PGP/MIME is
supported). In the @ref{Main view} the support is indicated by a big
letter @t{C} on the right hand side of the @t{mu4e} version. See
@ref{Decryption} and @ref{Verifying signatures}. For encryption and
signing messages, see @ref{Writing messages}.
@item @emph{How can I prevent @t{mu4e} from automatically marking messages as `read' when I read them?}
Set @code{mu4e-view-auto-mark-as-read} to @code{nil}.
@item @emph{Does @t{mu4e} support including all related messages in a thread,
like Gmail does?} Yes --- see @ref{Including related messages}.
@item @emph{There seems to be a lot of duplicate messages --- how can I get rid
of them?} See @ref{Skipping duplicates}.
@item @emph{How can I use the @t{eww} browser to view rich-text messages?}
With a new enough emacs, this happens automatically. See @ref{Html2text
functions} for some details.
@item @emph{Some messages are almost unreadable in emacs --- can I view them in
an external web browser?} Indeed, airlines often send messages that
heavily depend on html and are hard to digest inside emacs. Fortunately,
there's an @emph{action} (@ref{Message view actions})
defined for this. Simply add to your configuration:
@lisp
(add-to-list 'mu4e-view-actions
  '("ViewInBrowser" . mu4e-action-view-in-browser) t)
@end lisp
Now, when viewing such a difficult message, type @kbd{aV}, and the message
opens inside a webbrowser. You can influence the browser with
@code{browse-url-generic-program}; and see @ref{Privacy aspects}.
@item @emph{How can I read encrypted messages that I sent?}. Since you do not own the
recipient's key you typically cannot read those mails --- so the trick is
to encrypt outgoing mails with your key, too. This can be automated by
adding the following snippet to your configuration (courtesy of user
@t{kpachnis}):
@lisp
(require 'epg-config)
(setq mml2015-use 'epg
      epg-user-id "gpg_key_id"
      mml2015-encrypt-to-self t
      mml2015-sign-with-sender t)
@end lisp
@item @emph{view-as-pdf seems to hang for some e-mails --- what can I do about that?}
Short answer: install @t{nspluginwrapper}. Longer answer: @t{mu} comes
with @t{msg2pdf}, which is a program used to convert the messages to
pdf, and which depends on WebKit, which in some cases needs
@t{nspluginwrapper} and it waits for a long time if it's not there. So,
installing @t{nspluginwrapper} prevents that.
@item @emph{Can I `bounce' or `resend' messages?}
Yes --- it is possible to edit a (copy of) an existing message and then
send it, using @code{M-x mu4e-compose-resend}. This gives you a raw copy
of the message, including all headers, encoded parts and so on. Reason
for this is that for resending, it is important not to change anything
(except perhaps for the @t{To:} address when bouncing); since we cannot
losslessly decode an existing message, you get the raw version.

@end enumerate

@node Writing messages
@section Writing messages

@enumerate
@item @emph{What's the deal with replies to messages I wrote myself?} Like
many other mail-clients, @t{mu4e} treats replies to messages you wrote
yourself as special --- these messages keep the same @t{To:} and @t{Cc:}
as the original message. This is to ease the common case of following up
to a message you wrote earlier.
@item @emph{How can I automatically set the @t{From:}-address for a
reply-message, based on some field in the original?} See @ref{Compose hooks}.
@item @emph{And what about customizable folders for draft messages, sent
messages, trashed messages, based on e.g. the @t{From:} header?} See
@ref{Dynamic folders}.
@item @emph{Can I define aliases for (groups of) e-mail addresses?} Sure -
see @ref{(emacs) Mail Aliases}.
@item @emph{How can I automatically add some header to an outgoing message?}
Once more, see @ref{Compose hooks}.
@item @emph{How can I influence the way the original message looks when
replying or inline forwarding?} Since @code{mu4e-compose-mode} derives from
@code{message-mode}, you can re-use many of its facilities.
@inforef{Insertion Variables,,message}.
@item @emph{How can I easily include attachments in the messages I write?}
You can drag-and-drop from your desktop; alternatively, you can use @t{dired}
--- see @ref{Dired}.
@item @emph{@t{mu4e} seems to remove myself from the @t{Cc:}-list; how can I
prevent that?}  Set @code{mu4e-compose-keep-self-cc} to @t{t} in your
configuration.
@item @emph{How can I start a new message-thread from a reply?} Remove the @t{In-Reply-To} header,
and @t{mu4e} automatically removes the (hidden) @t{References} header as
well when sending it. This makes the message show up as a top-level
message rather than as a response.
@item @emph{How can I attach an existing message?} Use @code{mu4e-action-capture-message}
 (i.e., @kbd{a c} in the headers view) to `capture' the to-be-attached
 message, then when editing the message, use @kbd{M-x
 mu4e-compose-attach-captured-message}.
@item @emph{How can I sign or encrypt messages?} You can do so using @command{emacs}'
MIME-support --- check the @t{Attachments}-menu while composing a
message. Also see @ref{Signing and encrypting}.
@item @emph{Can I use @t{BBDB} with @t{mu4e}?} Yes, with the current
(2015-06-23) development release of BBDB
@url{http://savannah.nongnu.org/projects/bbdb/}, or releases of BBDB
after 3.1.2.
@ref{BBDB}.
@item @emph{After sending some messages, it seems the buffer for these
messages stay around. How can I get rid of those?}
@lisp
(setq message-kill-buffer-on-exit t)
@end lisp
@item @emph{Sending big messages is slow and blocks emacs --- what can I do
about it?} For this, there's @url{https://github.com/jwiegley/emacs-async}
(also available from the Emacs package repository); add the following snippet
to your configuration:
@lisp
(require 'smtpmail-async)
(setq
  send-mail-function 'async-smtpmail-send-it
  message-send-mail-function 'async-smtpmail-send-it)
@end lisp
With this, messages are sent using a background Emacs instance.

A word of warning though, this tends to not be as reliable as sending
the message in the normal, synchronous fashion, and people have reported
silent failures, where mail sending fails for some reason without any
indication of that.

You can check the progress of the background by checking the
@t{*Messages*}-buffer, which should show something like:
@verbatim
Delivering message to "William Shakespeare" <will@example.com>...
Mark set
Saving file /home/djcb/Maildir/sent/cur/20130706-044350-darklady:2,S...
Wrote /home/djcb/Maildir/sent/cur/20130706-044350-darklady:2,S
Sending...done
@end verbatim
The first and final messages are the most important, and there may be
considerable time between them, depending on the size of the message.
@item @emph{Is it possible to compose messages in a separate frame?}
Yes --- set the variable @code{mu4e-compose-in-new-frame} to @code{t}.
@item @emph{How can I apply format=flowed to my outgoing messages, enabling
receiving clients that support this feature to reflow my paragraphs?}
Plain text emails with @t{Content-Type: text/plain; format=flowed} can
be reflowed (i.e. line endings removed, paragraphs refilled) by
receiving clients that support this standard. Clients that don't support
this, show them as is, which means this feature is truly non-invasive.

Here's an explanatory blog post which also shows why this is a desirable
feature: @url{https://mathiasbynens.be/notes/gmail-plain-text} (if you
don't have it, your mails mostly look quite bad especially on mobile
devices) and here's the RFC with all the details:
@url{http://www.ietf.org/rfc/rfc2646.txt}.

Since version 0.9.17, @t{mu4e} send emails with @t{format=flowed} by
setting

@lisp
(setq mu4e-compose-format-flowed t)
@end lisp

@noindent
in your Emacs init file (@file{~/.emacs} or @file{~/.emacs.d/init.el}).
The transformation of your message into the proper format is
done at the time of sending.  For this to happen properly, you should
write each paragraph of your message of as a long line (i.e. without
carriage return).  If you introduce unwanted newlines in your paragraph,
use @kbd{M-q} to reformat it as a single line.

If you want to send the message with paragraphs on single lines but
without @t{format=flowed} (because, say, the receiver does not
understand the latter as it is the case for Google or Github), use
@kbd{M-x use-hard-newlines} (to turn @code{use-hard-newlines} off) or
uncheck the box @t{format=flowed} in the @t{Text} menu when composing a
message.

@end enumerate

@node Known issues
@section Known issues

Although they are not really @emph{questions}, we end this chapter with
a list of known issues and/or missing features in @t{mu4e}. Thus, users
won't have to search in vain for things that are not there (yet), and
the author can use it as a todo-list.

@itemize
@item @emph{mu4e does not work well if the @command{emacs} language environment is not
UTF-8}; so, if you encounter problems with encodings, be sure to have
@code{(set-language-environment "UTF-8")} in your @file{~/.emacs}.
@item @emph{Thread handling is incomplete.} While threads are calculated and are
visible in the headers buffer, you cannot collapse/open them.
@item @emph{The key-bindings are @emph{somewhat} hard-coded.} That is, the main
menu assumes the default key-bindings, as do the clicks-on-bookmarks.
@item @emph{The @t{emacs} front-end of the @t{notmuch} e-mail indexer
conflicts with @t{mu4e}}. @t{notmuch} running in parallel with
@t{mu4e} leads to
@verbatim
error in process filter: mu4e-error-handler: Error 70: cannot read
~/Maildir/...
@end verbatim
when sending a reply to some e-mail. This seems to be caused by
@t{notmuch} changing the name of the original message file while
@t{mu4e} is working on it. To prevent this, deactivate @t{notmuch} in
your Emacs setup.
@item @emph{The PDF-version of the manual does not show any of the non-ASCII
characters} --- this is because the @t{texi2pdf} documentation system does
not support those. There is not much we can do about that.
@end itemize

For a more complete list, please refer to the issues-list in the
github-repository.


@node Tips and Tricks
@appendix Tips and Tricks

@menu
* Fancy characters:: Non-ascii characters in the UI
* Multiple accounts:: (Obsolete) the old way to deal with multiple accounts
* Refiling messages:: Moving message to some archive folder
* Saving outgoing messages:: Automatically save sent messages
* Confirmation before sending:: Check messages before sending
@end menu

@node Fancy characters
@section Fancy characters

When using `fancy characters' (@code{mu4e-use-fancy-chars}) with the
@emph{Inconsolata}-font (and likely others as well), the display may be
slightly off; the reason for this issue is that Inconsolata does not
contain the glyphs for the `fancy' arrows and the glyphs that are used
as replacements are too high.

To fix this, you can use something like the following workaround (in
your @t{.emacs}-file):
@lisp
(if (equal window-system 'x)
    (progn
      (set-fontset-font "fontset-default" 'unicode "Dejavu Sans Mono")
      (set-face-font 'default "Inconsolata-10")))
@end lisp

Other fonts with good support for Unicode are @t{unifont} and
@t{symbola}.

For a more complete solution, but with greater overhead, you can also
try the @emph{unicode-fonts} package:
@lisp
(require 'unicode-fonts)
(require 'persistent-soft) ; To cache the fonts and reduce load time
(unicode-fonts-setup)
@end lisp


@node Multiple accounts
@section Multiple accounts

@b{Note}: for @t{mu4e} version 0.9.16 and higher, the recommended way
to deal with multiple accounts is through @t{mu4e}'s built-in
@ref{Contexts} system. For older versions, the below still works.

Using @t{mu4e} with multiple email accounts is fairly easy. Although
variables such as @code{user-mail-address}, @code{mu4e-sent-folder},
@code{message-*}, @code{smtpmail-*}, etc. typically only take one value,
it is easy to change their values using @code{mu4e-compose-pre-hook}.
The setup described here is one way of doing this (though certainly not
the only way).

This setup assumes that you have multiple mail accounts under
@code{mu4e-maildir}. As an example, we'll use @t{~/Maildir/Account1}
and @t{~/Maildir/Account2}, but the setup works just as well if
@code{mu4e-maildir} points to something else.

First, you need to make sure that all variables that you wish to change
based on user account are set to some initial value. So set up your
environment with e.g., your main account:

@lisp
(setq mu4e-sent-folder "/Account1/Saved Items"
      mu4e-drafts-folder "/Account1/Drafts"
      user-mail-address "my.address@@account1.example.com"
      smtpmail-default-smtp-server "smtp.account1.example.com"
      smtpmail-local-domain "account1.example.com"
      smtpmail-smtp-server "smtp.account1.example.com"
      smtpmail-stream-type 'starttls
      smtpmail-smtp-service 25)
@end lisp

Then create a variable @code{my-mu4e-account-alist}, which should
contain a list for each of your accounts. Each list should start with
the account name, (which @emph{must} be identical to the account's
directory name under @t{~/Maildir}), followed by @code{(variable
value)} pairs:

@lisp
(defvar my-mu4e-account-alist
  '(("Account1"
     (mu4e-sent-folder "/Account1/Saved Items")
     (mu4e-drafts-folder "/Account1/Drafts")
     (user-mail-address "my.address@@account1.example.com")
     (smtpmail-default-smtp-server "smtp.account1.example.com")
     (smtpmail-local-domain "account1.example.com")
     (smtpmail-smtp-user "username1")
     (smtpmail-smtp-server "smtp.account1.example.com")
     (smtpmail-stream-type starttls)
     (smtpmail-smtp-service 25))
    ("Account2"
     (mu4e-sent-folder "/Account2/Saved Items")
     (mu4e-drafts-folder "/Account2/Drafts")
     (user-mail-address "my.address@@account2.example.com")
     (smtpmail-default-smtp-server "smtp.account2.example.com")
     (smtpmail-local-domain "account2.example.com")
     (smtpmail-smtp-user "username2")
     (smtpmail-smtp-server "smtp.account2.example.com")
     (smtpmail-stream-type starttls)
     (smtpmail-smtp-service 587))))
@end lisp

You can put any variable you want in the account lists, just make sure
that you put in @emph{all} the variables that differ for each account.
Variables that do not differ need not be included. For example, if you
use the same SMTP server for both accounts, you don't need to include
the SMTP-related variables in @code{my-mu4e-account-alist}.

Note that some SMTP servers (such as Gmail) require the SMTP username to
match the user mail address. In this case, your mail appears to
originate from whichever SMTP account you use. Thus unless you are
certain your SMTP server does not have this requirement, you should
generally use different SMTP account credentials for each mail account.

Now, the following function can be used to select an account and set the
variables in @code{my-mu4e-account-alist} to the correct values:

@lisp
(defun my-mu4e-set-account ()
  "Set the account for composing a message."
  (let* ((account
          (if mu4e-compose-parent-message
              (let ((maildir (mu4e-message-field mu4e-compose-parent-message :maildir)))
                (string-match "/\\(.*?\\)/" maildir)
                (match-string 1 maildir))
            (completing-read (format "Compose with account: (%s) "
                                     (mapconcat #'(lambda (var) (car var))
                                                my-mu4e-account-alist "/"))
                             (mapcar #'(lambda (var) (car var)) my-mu4e-account-alist)
                             nil t nil nil (caar my-mu4e-account-alist))))
         (account-vars (cdr (assoc account my-mu4e-account-alist))))
    (if account-vars
        (mapc #'(lambda (var)
                  (set (car var) (cadr var)))
              account-vars)
      (error "No email account found"))))
@end lisp

This function then needs to be added to @code{mu4e-compose-pre-hook}:

@lisp
(add-hook 'mu4e-compose-pre-hook 'my-mu4e-set-account)
@end lisp

This way, @code{my-mu4e-set-account} is called every time you edit a
message. If you compose a new message, it simply asks you for the
account you wish to send the message from (TAB completion works). If
you're replying or forwarding a message, or editing an existing draft,
the account is chosen automatically, based on the first component of the
maildir of the message being replied to, forwarded or edited (i.e., the
directory under @t{~/Maildir}).

@node Refiling messages
@section Refiling messages

By setting @code{mu4e-refile-folder} to a function, you can dynamically
determine where messages are to be refiled. If you want to do this based
on the subject of a message, you can use a function that matches the
subject against a list of regexes in the following way. First, set up a
variable @code{my-mu4e-subject-alist} containing regexes plus associated
mail folders:

@lisp
(defvar my-mu4e-subject-alist '(("kolloqui\\(um\\|a\\)" . "/Kolloquium")
                                ("Calls" . "/Calls")
                                ("Lehr" . "/Lehre")
                                ("webseite\\|homepage\\|website" . "/Webseite"))
  "List of subjects and their respective refile folders.")
@end lisp

Now you can use the following function to automatically refile messages
based on their subject line:

@lisp
(defun my-mu4e-refile-folder-function (msg)
  "Set the refile folder for MSG."
  (let ((subject (mu4e-message-field msg :subject))
        (folder (or (cdar (member* subject my-mu4e-subject-alist
                                   :test #'(lambda (x y)
                                             (string-match (car y) x))))
                    "/General")))
    folder))
@end lisp

Note the @t{"/General"} folder: it is the default folder in case the
subject does not match any of the regexes in
@code{my-mu4e-subject-alist}.

In order to make this work, you'll of course need to set
@code{mu4e-refile-folder} to this function:

@lisp
(setq mu4e-refile-folder 'my-mu4e-refile-folder-function)
@end lisp

If you have multiple accounts, you can accommodate them as well:

@lisp
(defun my-mu4e-refile-folder-function (msg)
  "Set the refile folder for MSG."
  (let ((maildir (mu4e-message-field msg :maildir))
        (subject (mu4e-message-field msg :subject))
        folder)
    (cond
     ((string-match "Account1" maildir)
      (setq folder (or (catch 'found
                         (dolist (mailing-list my-mu4e-mailing-lists)
                           (if (mu4e-message-contact-field-matches
                             msg :to (car mailing-list))
                               (throw 'found (cdr mailing-list)))))
                       "/Account1/General")))
     ((string-match "Gmail" maildir)
      (setq folder "/Gmail/All Mail"))
     ((string-match "Account2" maildir)
      (setq folder (or (cdar (member* subject my-mu4e-subject-alist
                                      :test #'(lambda (x y)
                                                (string-match
                                                   (car y) x))))
                       "/Account2/General"))))
    folder))
@end lisp

This function actually uses different methods to determine the refile
folder, depending on the account: for @emph{Account2}, it uses
@code{my-mu4e-subject-alist}, for the @emph{Gmail} account it simply uses the
folder ``All Mail''. For Account1, it uses another method: it files the
message based on the mailing list to which it was sent. This requires
another variable:

@lisp
(defvar my-mu4e-mailing-lists
  '(("mu-discuss@@googlegroups.com" . "/Account1/mu4e")
    ("pandoc-discuss@@googlegroups.com" . "/Account1/Pandoc")
    ("auctex@@gnu.org" . "/Account1/AUCTeX"))
  "List of mailing list addresses and folders where
   their messages are saved.")
@end lisp

@node Saving outgoing messages
@section Saving outgoing messages

Like @code{mu4e-refile-folder}, the variable @code{mu4e-sent-folder} can also
be set to a function, in order to dynamically determine the save folder. One
might, for example, wish to automatically put messages going to mailing lists
into the trash (because you'll receive them back from the list anyway). If you
have set up the variable @code{my-mu4e-mailing-lists} as mentioned, you can
use the following function to determine a save folder:

@lisp
(defun my-mu4e-sent-folder-function (msg)
  "Set the sent folder for the current message."
  (let ((from-address (message-field-value "From"))
        (to-address (message-field-value "To")))
    (cond
     ((string-match "my.address@@account1.example.com" from-address)
      (if (member* to-address my-mu4e-mailing-lists
                   :test #'(lambda (x y)
                             (string-match (car y) x)))
          "/Trash"
        "/Account1/Sent"))
     ((string-match "my.address@@gmail.com" from-address)
      "/Gmail/Sent Mail")
     (t (mu4e-ask-maildir-check-exists "Save message to maildir: ")))))
@end lisp

Note that this function doesn't use @code{(mu4e-message-field msg
:maildir)} to determine which account the message is being sent from.
The reason is that the function in @code{mu4e-sent-folder} is
called when you send the message, but before @t{mu4e} has created the
message struct from the compose buffer, so that
@code{mu4e-message-field} cannot be used. Instead, the function uses
@code{message-field-value}, which extracts the values of the headers in
the compose buffer. This means that it is not possible to extract the
account name from the message's maildir, so instead the from address is
used to determine the account.

Again, the function shows three different possibilities: for the first
account (@t{my.address@@account1.example.com}) it uses
@code{my-mu4e-mailing-lists} again to determine if the message goes to a
mailing list. If so, the message is put in the trash folder, if not, it
is saved in @t{/Account1/Sent}. For the second (Gmail) account, sent
mail is simply saved in the Sent Mail folder.

If the from address is not associated with Account1 or with the Gmail
account, the function uses @code{mu4e-ask-maildir-check-exists} to ask
the user for a maildir to save the message in.

@node Confirmation before sending
@section Confirmation before sending

To protect yourself from sending messages too hastily, you can add a
final confirmation, which you can of course make as elaborate as you
wish.

@lisp
(add-hook 'message-send-hook
  (lambda ()
    (unless (yes-or-no-p "Sure you want to send this?")
      (signal 'quit nil))))
@end lisp

@node How it works
@appendix How it works

While perhaps not interesting for all users of @t{mu4e}, some curious
souls may want to know how @t{mu4e} does its job.

@menu
* High-level overview::How the pieces fit together
* mu server::The mu process running in the background
* Reading from the server::Processing responses from the server
* The message s-expression::What messages look like from the inside
@end menu

@node High-level overview
@section High-level overview

At a high level, we can summarize the structure of the @t{mu4e} system using
some ascii-art:

@cartouche
@example
              +---------+
              | emacs   |
              |    +------+
              +----| mu4e | --> send mail (smtpmail)
                   +------+
                    |  A
                    V  |  ---/ search, view, move mail
              +---------+    \
              |   mu    |
              +---------+
                |    A
                V    |
              +---------+
              | Maildir |  <--- receive mail (fetchmail,
              +---------+                     offlineimap, ...)
@end example
@end cartouche

In words:
@itemize
@item Your e-mail messages are stored in a Maildir-directory
(typically, @file{~/Maildir} and its subdirectories), and new mail comes in
using tools like @t{fetchmail}, @t{offlineimap}, or through a local mail
server.
@item @t{mu} indexes these messages periodically, so you can quickly search for
them. @t{mu} can run in a special @t{server}-mode, where it provides services
 to client software.
@item @t{mu4e}, which runs inside @command{emacs} is
 such a client; it communicates with @command{mu} (in its @t{server}-mode) to
 search for messages, and manipulate them.
@item @t{mu4e} uses the facilities
 offered by @command{emacs} (the Gnus message editor and @t{smtpmail}) to send
 messages.
@end itemize

@node mu server
@section @t{mu server}

@t{mu4e} is based on the @t{mu} e-mail searching/indexer. The latter is a
C-program; there are different ways to communicate with a client that is
emacs-based.

One way to implement this, would be to call the @t{mu} command-line tool with
some parameters and then parse the output. In fact, that was the first
approach --- @t{mu4e} would invoke e.g., @t{mu find} and process the output in
@command{emacs}.

However, with this approach, we need to load the entire e-mail @emph{Xapian}
database (in which the message is stored) for each invocation. Wouldn't it be
nicer to keep a running @t{mu} instance around?  Indeed, it would --- and thus,
the @t{mu server} sub-command was born. Running @t{mu server} starts a simple
shell, in which you can give commands to @command{mu}, which then spits out
the results/errors. @command{mu server} is not meant for humans, but it can be
used manually, which is great for debugging.

@node Reading from the server
@section Reading from the server

In the design, the next question was what format @t{mu} should use for its
output for @t{mu4e} (@command{emacs}) to process. Some other programs use
@abbr{JSON} here, but it seemed easier (and possibly, more efficient) just to
talk to @command{emacs} in its native language: @emph{s-expressions}, and
interpret those using the @command{emacs}-function
@code{read-from-string}. See @ref{The message s-expression} for details on the
format.

So, now let's look at how we process the data from @t{mu server} in
@command{emacs}. We'll leave out a lot of details, @t{mu4e}-specifics, and look
at a bit more generic approach.

The first thing to do is to create a process (for example, with
@code{start-process}), and then register a filter function for it, which is
invoked whenever the process has some data for us. Something like:

@lisp
  (let ((proc (start-process <arguments>)))
    (set-process-filter proc 'my-process-filter)
    (set-process-sentinel proc 'my-process-sentinel))
@end lisp

Note, the process sentinel is invoked when the process is terminated --- so
there you can clean things up. The function @code{my-process-filter} is a
user-defined function that takes the process and the chunk of output as
arguments; in @t{mu4e} it looks something like (pseudo-lisp):

@lisp
(defun my-process-filter (proc str)
  ;; mu4e-buf: a global string variable to which data gets appended
  ;; as we receive it
  (setq mu4e-buf (concat mu4e-buf str))
  (when <we-have-received-a-full-expression>
      <eat-expression-from mu4e-buf>
      <evaluate-expression>))
@end lisp

@code{<evaluate-expression>} de-multiplexes the s-expression we got. For
example, if the s-expression looks like an e-mail message header, it is
processed by the header-handling function, which appends it to the header
list. If the s-expression looks like an error message, it is reported to the
user. And so on.

The language between frontend and backend is documented in the @t{mu-server}
man-page. @t{mu4e} can log these communications; you can use @kbd{M-x
mu4e-toggle-logging} to turn logging on and off, and you can view the log
using @kbd{M-x mu4e-show-log} (@key{$}).

@node The message s-expression
@section The message s-expression

A typical message s-expression looks something like the following:

@lisp
(:docid 32461
 :from (("Nikola Tesla" . "niko@@example.com"))
 :to (("Thomas Edison" . "tom@@example.com"))
 :cc (("Rupert The Monkey" . "rupert@@example.com"))
 :subject "RE: what about the 50K?"
 :date (20369 17624 0)
 :size 4337
 :message-id "C8233AB82D81EE81AF0114E4E74@@123213.mail.example.com"
 :path  "/home/tom/Maildir/INBOX/cur/133443243973_1.10027.atlas:2,S"
 :maildir "/INBOX"
 :priority normal
 :flags (seen)
 :parts ( (:index 1 :mime-type "text/plain" :size 12345 :attachment nil)
          (:index 2 :name "photo.jpg" :mime-type "image/jpeg"
           :size 147331 :attachment t)
          (:index 3 :name "book.pdf" :mime-type "application/pdf"
           :size 192220 :attachment t))
 :references  ("C8384574032D81EE81AF0114E4E74@@123213.mail.example.com"
 "38203498230942D81EE81AF0114E4E74@@123213.mail.example.com")
 :in-reply-to "38203498230942D81EE81AF0114E4E74@@123213.mail.example.com"
 :body-txt "Hi Tom,
 ....
")
@end lisp

This s-expression forms a property list (@t{plist}), and we can get values
from it using @t{plist-get}; for example @code{(plist-get msg :subject)} would
get you the message subject. However, it's better to use the function
@code{mu4e-message-field} to shield you from some of the implementation
details that are subject to change; and see the other convenience functions in
@file{mu4e-message.el}.

Some notes on the format:
@itemize
@item The address fields are @emph{lists} of pairs @code{(name . email)},
where @t{name} can be @t{nil}.
@item The date is in format @command{emacs} uses (for example in
@code{current-time}).@footnote{Emacs 32-bit integers have only 29 bits
available for the actual number; the other bits are use by @command{emacs} for
internal purposes. Therefore, we need to split @t{time_t} in two numbers.}
@item Attachments are a list of elements with fields @t{:index} (the number of
the MIME-part), @t{:name} (the file name, if any), @t{:mime-type} (the
MIME-type, if any) and @t{:size} (the size in bytes, if any).
@item Messages in the @ref{Headers view} come from the database and do not have
@t{:attachments}. @t{:body-txt} or @t{:body-html} fields. Message in the
@ref{Message view} use the actual message file, and do include these fields.
@end itemize

@subsection Example: ping-pong

As an example of the communication between @t{mu4e} and @command{mu}, let's
look at the @t{ping-pong}-sequence. When @t{mu4e} starts, it sends a command
@t{ping} to the @t{mu server} backend, to learn about its version. @t{mu
server} then responds with a @t{pong} s-expression to provide this information
(this is implemented in @file{mu-cmd-server.c}).

We start this sequence when @t{mu4e} is invoked (when the program is
started). It calls @t{mu4e-proc-ping}, and registers a (lambda) function for
@t{mu4e-proc-pong-func}, to handle the response.

@verbatim
-> cmd:ping
<- (pong "mu" :version "x.x.x" :doccount 10000)
@end verbatim

When we receive such a @t{pong} (in @file{mu4e-proc.el}), the lambda function
we registered is called, and it compares the version we got from the @t{pong}
with the version we expected, and raises an error if they differ.

@node Logging and debugging
@appendix Logging and debugging

As explained in @ref{How it works}, @t{mu4e} communicates with its backend
(@t{mu server}) by sending commands and receiving responses (s-expressions).

For debugging purposes, it can be very useful to see this data. For this
reason, @t{mu4e} can log all these messages. Note that the `protocol' is
documented to some extent in the @t{mu-server} manpage.

You can enable (and disable) logging with @kbd{M-x mu4e-toggle-logging}. The
log-buffer is called @t{*mu4e-log*}, and in the @ref{Main view}, @ref{Headers
view} and @ref{Message view}, there's a keybinding @key{$} that takes you
there. You can quit it by pressing @key{q}.

Logging can be a bit resource-intensive, so you may not want to leave it on
all the time. By default, the log only maintains the most recent 1200
lines. @t{mu} itself keeps a log as well, you can find this it in
@t{<MUHOME>/log/mu.log}, typically @t{~/.mu/log/mu.log}.

@node GNU Free Documentation License
@appendix GNU Free Documentation License

@include fdl.texi

@bye
