mostly cosmics

[notmuch-wiki] / emacstips.mdwn

# Tips and Tricks for using notmuch with Emacs

One of the more popular notmuch message reading clients is
**notmuch.el**, an [emacs](http://www.gnu.org/software/emacs/) major
mode for interacting with notmuch.  It is included in the notmuch
package (notmuch-emacs in Debian).  This page goes over some usage
tips for using notmuch with Emacs.

[[!toc levels=2]]

## Setup

Have a look at the [Howto](http://notmuchmail.org/howto/) for
prerequisites.  Be sure you have done the general setup using the
notmuch cli command!

To use the Notmuch emacs mode, first add the following line to your
`.emacs` rc file:

        (require 'notmuch)

or you can load the package via autoload:

        (autoload 'notmuch "notmuch" "notmuch mail" t)

Then, either run "emacs -f notmuch", or execute the command `M-x
notmuch` from within a running emacs.

## Navigating & reading mails

When first starting notmuch in emacs, you will be presented with the
notmuch "hello" page.  If it exits with an error after writing
"Welcome to notmutch. You have" you need to do the basic notmuch setup
first (see above).
From here you can do searches, see lists of recent
searches, saved searches, message tags, help information, etc.

Executing a search will open a new buffer in `notmuch-search-mode`
displaying the search results.  Each line in the search results
represents a message thread.  Hitting the '?' key will show help for
this mode.

In general, the 'q' will kill the current notmuch buffer and return
you to the previous buffer (sort of like a 'pop').

In search mode, navigating to a thread and hitting return will then
open a new buffer in `notmuch-show-mode`, which will show the actual
message contents of the thread.

## Sending mail

In any notmuch mode, you can start a new message by hitting the 'm'
key.  To reply to a message or thread, just hit the 'r' key.

When composing new messages, you will be entered in emacs's
`message-mode`, which is a powerful mode for composing and sending
messages.  When in message mode, you can type `C-c ?` for help.

If you would like to use address autocompletion when composing
messages, see [address completion](#address_completion).

When you are ready to send a message, type `C-c C-c`. By default
message mode will use your sendmail command to send mail, so make sure
that works. One annoying standard configuration of message mode is
that it will hide the sent mail in your emacs frame stack, but it will
not close it. If you type several mails in an emacs session they will
accumulate and make switching between buffers more annoying. You can
avoid that behavior by adding `(setq message-kill-buffer-on-exit t)`
in your `.emacs` file (or doing `M-x
customize-variable<RET>message-kill-buffer-on-exit<RET>`) which will
really close the mail window after sending it.

## Attaching files

Using the `M-x mml-attach-file` command, you can attach any file to be
sent with your mail. By default this command is bound to the menu item
*Attachments--Attach File* with the key binding `C-c C-a`. The
variable `mml-dnd-attach-options` (`M-x
customize-variable<RET>mml-dnd-attach-options<RET>`) can be set to
allow the prompting for various attachment options (such as
inline/attachment) if you want to do that.

For those who prefer a more graphical interface, you can also simply
drag and drop files from a file manager into a mail composition window
to have them attached. In Ubuntu this works without any modifications
if files are dragged from the file manager.

And for those who prefer working from command line, the following
script opens new emacs window with empty message and attaches files
mentioned as script arguments. (Note: The script expects that you have
`(server-start)` in your `.emacs` file.)

        #!/bin/sh
        attach_cmds=""
        while [ "$1" ]; do
            fullpath=$(readlink --canonicalize "$1")
            attach_cmds="$attach_cmds (mml-attach-file \"$fullpath\")"
            shift
        done
        emacsclient -a '' -c -e "(progn (compose-mail) $attach_cmds)"

## Issues with Emacs 24

If notmuch-show-mode behaves badly for you in emacs 24.x try adding one of

        (setq gnus-inhibit-images nil)

or

        (require 'gnus-art)

to your .emacs file.

-----

# Advanced tips and tweaks

## Use separate emacs lisp file for notmuch configuration

Instead of adding notmuch configuration code to `.emacs`, there
is an option to collect those to a separate file (which is only
loaded when `notmuch` is invoked). To do this, write, for example
a file called `~/.emacs.d/my-notmuch.el`:

        ;;; my-notmuch.el -- my notmuch mail configuration
        ;;;

        ;;; add here stuff required to be configured *before*
        ;;; notmuch is loaded;

        ;; uncomment and modify in case some elisp files are not found in load-path
        ;; (add-to-list 'load-path "~/vc/ext/notmuch/emacs")

        ;;; load notmuch
        (require 'notmuch)

        ;;; add here stuff required to be configured *after*
        ;;; notmuch is loaded;

        ;; uncomment & modify if you want to use external smtp server to send mail
        ;; (setq smtpmail-smtp-server "smtp.server.tld"
        ;;       message-send-mail-function 'message-smtpmail-send-it)
        ;; uncomment to debug smtp sending problems
        ;; (setq smtpmail-debug-info t)

Then, add to `.emacs`:

        (autoload 'notmuch "~/.emacs.d/my-notmuch" "notmuch mail" t)

## Initial cursor position in notmuch 0.15 hello window

In notmuch version 0.15 emacs client the handling of cursor position in
notmuch hello window has been simplified to a version which suits best
most cases.

Initially the cursor is positioned at the beginning of buffer.

Some users liked the "ancient" version where cursor was moved to the
first `Saved searches` button.

Add the following code to your notmuch emacs configuration file in
case you want this behaviour:

        (add-hook 'notmuch-hello-refresh-hook
                  (lambda ()
                    (if (and (eq (point) (point-min))
                             (search-forward "Saved searches:" nil t))
                        (progn
                          (forward-line)
                          (widget-forward 1))
                      (if (eq (widget-type (widget-at)) 'editable-field)
                          (beginning-of-line)))))

## Add a key binding to add/remove/toggle a tag

The `notmuch-{search,show}-{add,remove}-tag` functions are very useful
for making quick tag key bindings.  For instance, here's an example
of how to make a key binding to add the "spam" tag and remove the
"inbox" tag in notmuch-show-mode:

In notmuch versions up to 0.11.x

        (define-key notmuch-show-mode-map "S"
          (lambda ()
            "mark message as spam"
            (interactive)
            (notmuch-show-add-tag "spam")
            (notmuch-show-remove-tag "inbox")))

Starting from notmuch 0.12 the functions `notmuch-show-add-tag` and
`notmuch-show-remove-tag` have changed to be more versatile and lost
noninteractive use. When upgrading to 0.12 the above needs to be
changed to this:

        (define-key notmuch-show-mode-map "S"
          (lambda ()
            "mark message as spam"
            (interactive)
            (notmuch-show-tag-message "+spam" "-inbox")))

You can do the same for threads in `notmuch-search-mode` by just
replacing "show" with "search" in the called functions.

Starting from notmuch 0.12 use `notmuch-search-tag-thread` instead:

        (define-key notmuch-search-mode-map "S"
          (lambda ()
            "mark messages in thread as spam"
            (interactive)
            (notmuch-show-tag-thread "+spam" "-inbox")))

Starting from notmuch 0.13 use `notmuch-search-tag` -- it has a little
different usage syntax:

        (define-key notmuch-search-mode-map "S"
          (lambda ()
            "mark messages in thread as spam"
            (interactive)
            (notmuch-search-tag '("+spam" "-inbox"))))

The definition above makes use of a lambda function, but you could
also define a separate function first:

        (defun notmuch-show-tag-spam ()
          "mark message as spam"
          (interactive)
          (notmuch-show-add-tag "spam")
          (notmuch-show-remove-tag "inbox")))
        (define-key notmuch-show-mode-map "S" 'notmuch-show-tag-spam)

(See above for analogy how to apply this for notmuch 0.12 and later)

Here's a more complicated example of how to add a toggle "deleted"
key:

        (define-key notmuch-show-mode-map "d"
          (lambda ()
            "toggle deleted tag for message"
            (interactive)
            (if (member "deleted" (notmuch-show-get-tags))
                (notmuch-show-remove-tag "deleted")
              (notmuch-show-add-tag "deleted"))))

And version for notmuch 0.12

        (define-key notmuch-show-mode-map "d"
          (lambda ()
            "toggle deleted tag for message"
            (interactive)
            (notmuch-show-tag-message
              (if (member "deleted" (notmuch-show-get-tags))
                  "-deleted" "+deleted"))))

## Adding many tagging keybindings

If you want to have have many tagging keybindings, you can save the typing
the few lines of  boilerplate for every binding (for versions before 0.12,
you will need to change notmuch-show-apply-tag-macro).

    (eval-after-load 'notmuch-show
      '(define-key notmuch-show-mode-map "`" 'notmuch-show-apply-tag-macro))

    (setq notmuch-show-tag-macro-alist
      (list
       '("m" "+notmuch::patch" "+notmuch::moreinfo" "-notmuch::needs-review")
       '("n" "+notmuch::patch" "+notmuch::needs-review" "-notmuch::pushed")
       '("o" "+notmuch::patch" "+notmuch::obsolete"
             "-notmuch::needs-review" "-notmuch::moreinfo")
       '("p" "-notmuch::pushed" "-notmuch::needs-review"
         "-notmuch::moreinfo" "+pending")
       '("P" "-pending" "-notmuch::needs-review" "-notmuch::moreinfo" "+notmuch::pushed")
       '("r" "-notmuch::patch" "+notmuch::review")
       '("s" "+notmuch::patch" "-notmuch::obsolete" "-notmuch::needs-review" "-notmuch::moreinfo" "+notmuch::stale")
       '("t" "+notmuch::patch" "-notmuch::needs-review" "+notmuch::trivial")
       '("w" "+notmuch::patch" "+notmuch::wip" "-notmuch::needs-review")))

    (defun notmuch-show-apply-tag-macro (key)
      (interactive "k")
      (let ((macro (assoc key notmuch-show-tag-macro-alist)))
        (apply 'notmuch-show-tag-message (cdr macro))))

## Restore reply-to-all key binding to 'r'

Starting from notmuch 0.12 the 'r' key is bound to reply-to-sender instead of
reply-to-all. Here's how to swap the reply to sender/all bindings in show mode:

        (define-key notmuch-show-mode-map "r" 'notmuch-show-reply)
        (define-key notmuch-show-mode-map "R" 'notmuch-show-reply-sender)

And in search mode:

        (define-key notmuch-search-mode-map "r" 'notmuch-search-reply-to-thread)
        (define-key notmuch-search-mode-map "R" 'notmuch-search-reply-to-thread-sender)


## How to do FCC/BCC...

The Emacs interface to notmuch will automatically add an `Fcc`
header to your outgoing mail so that any messages you send will also
be saved in your mail store. You can control where this copy of the
message is saved by setting the variable `notmuch-fcc-dirs` which defines the
subdirectory relative to the `database.path` setting from your
notmuch configuration in which to save the mail. Enter a directory
(without the maildir `/cur` ending which will be appended
automatically). Additional information can be found as usual using:

       M-x describe-variable notmuch-fcc-dirs

An additional variable that can affect FCC settings in some cases is
`message-directory`. Emacs message-mode uses this variable for
postponed messages.

To customize both variables at the same time, use the fancy command:

        M-x customize-apropos<RET>\(notmuch-fcc-dirs\)\|\(message-directory\)

This mechanism also allows you to select different folders to be
used for the outgoing mail depending on your selected `From`
address. Please see the documentation for the variable
`notmuch-fcc-dirs` in the customization window for how to arrange
this.

## How to customize `notmuch-saved-searches`

When starting notmuch, a list of saved searches and message counts is
displayed, replacing the older `notmuch-folders` command. The set of
saved searches displayed can be modified directly from the notmuch
interface (using the `[save]` button next to a previous search) or by
customising the variable `notmuch-saved-searches`.

An example setting might be:

        (setq notmuch-saved-searches '(("inbox" . "tag:inbox")
                        ("unread" . "tag:inbox AND tag:unread")
                        ("notmuch" . "tag:inbox AND to:notmuchmail.org")))

Of course, you can have any number of saved searches, each configured
with any supported search terms (see "notmuch help search-terms").

Some users find it useful to add `and not tag:delete` to those
searches, as they use the `delete` tag to mark messages as
deleted. This causes messages that are marked as deleted to be removed
from the commonly used views of messages.  Use whatever seems most
useful to you.

## Viewing HTML messages with an external viewer

The emacs client can display an HTML message inline using either the
`html2text` library or some text browser, like w3m or lynx. This is
controlled by the `mm-text-html-renderer` variable.

The first option is theorically better, because it can generate
strings formatted for emacs and do whatever you want, e.g., substitute
text inside &lt;b&gt; tags for bold text in the buffer. The library, however
is still in a very early development phase and cannot yet process
properly many elements, like tables and <style> directives, and even
the generated text is often poorly formatted.

Among the available browsers, w3m seems to do a better job converting
the html, and if you have the w3m emacs package, you can use it,
instead of the w3m-standalone, and thus preserve the text formatting.

But if the rendering fails for one reason or another, or if you really
need to see the graphical presentation of the HTML message, it can be
useful to display the message in an external viewer, such as a web
browser. Here's a little script that Keith Packard wrote, which he
calls `view-html`:

        #!/bin/sh
        dir=`mktemp -d`
        trap "rm -r $dir" 0
        cat "$@" > "$dir"/msg
        if munpack -C "$dir" -t < "$dir"/msg 2>&1 | grep 'Did not find'; then
            sed -n '/[Hh][Tt][Mm][Ll]/,$p' "$dir"/msg > $dir/part1.html
            rm "$dir"/msg
        fi
        for i in "$dir"/part*; do
            if grep -q -i -e '<html>' -e 'text/html' "$i"; then
                iceweasel "$i" &
                sleep 3
                exit 0
            fi
        done

Save that script somewhere in your `${PATH}`, make it executable,
and change the invocation of `iceweasel` to any other HTML viewer if
necessary. Then within the emacs client, press '|' to pipe the
current message, then type "view-html".

Keith mentions the following caveat, "Note that if iceweasel isn't
already running, it seems to shut down when the script exits. I
don't know why."

## msmtp, message mode and multiple accounts

As an alternative to running a mail server such as sendmail or postfix
just to send email, it is possible to use
[msmtp](http://msmtp.sourceforge.net/). This small application will
look like `/usr/bin/sendmail` to a MUA such as emacs message mode, but
will just forward the email to an external SMTP server. It's fairly
easy to set up and it supports several accounts for using different
SMTP servers. The msmtp pages have several examples.

A typical scenario is that you want to use the company SMTP server
for email coming from your company email address, and your personal
server for personal email.  If msmtp is passed the envelope address
on the command line (the -f/--from option) it will automatically
pick the matching account.  The only trick here seems to be getting
emacs to actually pass the envelope from.  There are a number of
overlapping configuration variables that control this, and it's a
little confusion, but setting these three works for me:

 - `mail-specify-envelope-from`: `t`

 - `message-sendmail-envelope-from`: `header`

 - `mail-envelope-from`: `header`

With that in place, you need a `.msmtprc` with the accounts configured
for the domains you want to send out using specific SMTP servers and
the rest will go to the default account.

If you have a hard time getting the above to work for you, as I did,
it's also possible to add a message-send-mail-hook in your .emacs to
send the from header explicitly as an argument to msmtp as described
[here](http://www.emacswiki.org/cgi-bin/wiki/GnusMSMTP#toc2) on the
emacswiki.


## <span id="address_completion">Address completion when composing</span>

There are currently three solutions to this:

### bbdb

[bbdb](http://bbdb.sourceforge.net) is a contact database for emacs
that works quite nicely together with message mode, including
address autocompletion.

### notmuch database as an address book

You can also use the notmuch database as a mail address book itself.
To do this you need a command line tool that outputs likely address
candidates based on a search string.  There are currently three
available:

  * The python tool `notmuch_address.py` (`git clone
    http://commonmeasure.org/~jkr/git/notmuch_addresses.git`) (slower, but
    no compilation required so good for testing the setup)

  * The vala-based
    [addrlookup](http://github.com/spaetz/vala-notmuch) (faster, but
    needs compiling).  The addrlookup binary needs to be compiled.
    Grab
    `http://github.com/spaetz/vala-notmuch/raw/static-sources/src/addrlookup.c`
    and build it with:

            cc -o addrlookup addrlookup.c `pkg-config --cflags --libs gobject-2.0` -lnotmuch

  * Shell/fgrep/perl combination [nottoomuch-addresses.sh](http://www.iki.fi/too/nottoomuch/nottoomuch-addresses/).
    This tools maintains it's own address "database" gathered from email
    files notmuch knows and search from that "database" is done by `fgrep(1)`.

You can perform tab-completion using any of these programs.
Just add the following to your .emacs:

        (require 'notmuch-address)
        (setq notmuch-address-command "/path/to/address_fetching_program")
        (notmuch-address-message-insinuate)

### Google Contacts

[GooBook](http://code.google.com/p/goobook/) is a command-line tool for
accessing Google Contacts. Install and set it up according to its documentation.

To use GooBook with notmuch, use this wrapper script and set it up like the
programs above.

        #!/bin/sh
        goobook query "$*" | sed 's/\(.*\)\t\(.*\)\t.*/\2 \<\1\>/' | sed '/^$/d'

You can add the sender of a message to Google Contacts by piping the message
(`notmuch-show-pipe-message`) to `goobook add`.

## How to sign/encrypt messages with gpg

Messages can by signed using gpg by invoking
`M-x mml-secure-sign-pgpmime` (or `M-x mml-secure-encrypt-pgpmime`).
These functions are available via the standard `message-mode` keybindings
`C-c C-m s p` and `C-c C-m c p`. To sign outgoing mail by default, use the
`message-setup-hook` in your `.emacs` file:

        ;; Sign messages by default.
        (add-hook 'message-setup-hook 'mml-secure-sign-pgpmime)

This inserts the required `<#part sign=pgpmime>` into the beginning
of the mail text body and will be converted into a pgp signature
when sending (so one can just manually delete that line if signing
is not required).

Alternatively, you may prefer to use `mml-secure-message-sign-pgpmime` instead
of `mml-secure-sign-pgpmime` to sign the whole message instead of just one
part.

### Troubleshooting message-mode gpg support

- If you have trouble with expired subkeys, you may have encountered
  emacs bug #7931.  This is fixed in git commit 301ea744c on
  2011-02-02.  Note that if you have the Debian package easypg
  installed, it will shadow the fixed version of easypg included with
  emacs.

## Multiple identities using gnus-alias

[gnus-alias](http://www.emacswiki.org/emacs/GnusAlias) allows you to
define multiple identities when using `message-mode`. You can specify
the from address, organization, extra headers (including *Bcc*), extra
body text, and signature for each identity. Identities are chosen
based on a set of rules. When you are in message mode, you can switch
identities using gnus-alias.

### Installation

- put `gnus-alias.el` on your load Emacs-Lisp load path (add new directory
  to load path by writing `(add-to-list 'load-path "/some/load/path")` into
  your `.emacs`.

- Add the following to your `.emacs`

        (autoload 'gnus-alias-determine-identity "gnus-alias" "" t)
        (add-hook 'message-setup-hook 'gnus-alias-determine-identity)

Looking into `gnus-alias.el` gives a bit more information...

### Example Configuration

Here is an example configuration.

        ;; Define two identities, "home" and "work"
        (setq gnus-alias-identity-alist
              '(("home"
                 nil ;; Does not refer to any other identity
                 "John Doe <jdoe@example.net>" ;; Sender address
                 nil ;; No organization header
                 nil ;; No extra headers
                 nil ;; No extra body text
                 "~/.signature")
                ("work"
                 nil
                 "John Doe <john.doe@example.com>"
                 "Example Corp."
                 (("Bcc" . "john.doe@example.com"))
                 nil
                 "~/.signature.work")))
        ;; Use "home" identity by default
        (setq gnus-alias-default-identity "home")
        ;; Define rules to match work identity
        (setq gnus-alias-identity-rules
              '(("work" ("any" "john.doe@\\(example\\.com\\|help\\.example.com\\)" both) "work"))
        ;; Determine identity when message-mode loads
        (add-hook 'message-setup-hook 'gnus-alias-determine-identity)

When `gnus-alias` has been loaded (using autoload, require, *M-x load-library*
or *M-x load-file* (load-file takes file path -- therefore it can be used
without any `.emacs` changes)) the following commands can be used to get(/set)
more information (some of these have "extensive documentation"):

        M-x describe-variable RET gnus-alias-identity-alist
        M-x describe-variable RET gnus-alias-identity-rules
        M-x describe-variable RET gnus-alias-default-identity

        M-x customize-group RET gnus-alias RET
          or
        M-x gnus-alias-customize RET

The last two do the same thing.

See also the **Usage:** section in `gnus-alias.el`.

## Resending (or bouncing) messages

Add the following to your `.emacs` to be able to resend the current message in
show mode.

        (define-key notmuch-show-mode-map "b"
          (lambda (&optional address)
            "Bounce the current message."
            (interactive "sBounce To: ")
            (notmuch-show-view-raw-message)
            (message-resend address)))

## `notmuch-hello` refresh status message

Add the following to your `.emacs` to get a status message about the change in
the number of messages in the mail store when refreshing the `notmuch-hello`
buffer.

        (defvar notmuch-hello-refresh-count 0)

        (defun notmuch-hello-refresh-status-message ()
          (unless no-display
            (let* ((new-count
                    (string-to-number
                     (car (process-lines notmuch-command "count"))))
                   (diff-count (- new-count notmuch-hello-refresh-count)))
              (cond
               ((= notmuch-hello-refresh-count 0)
                (message "You have %s messages."
                         (notmuch-hello-nice-number new-count)))
               ((> diff-count 0)
                (message "You have %s more messages since last refresh."
                         (notmuch-hello-nice-number diff-count)))
               ((< diff-count 0)
                (message "You have %s fewer messages since last refresh."
                         (notmuch-hello-nice-number (- diff-count)))))
              (setq notmuch-hello-refresh-count new-count))))

        (add-hook 'notmuch-hello-refresh-hook 'notmuch-hello-refresh-status-message)

## Replacing tabs with spaces in subject and header

Mailman mailing list software rewrites and rewraps long message subjects in
a way that causes TABs to appear in the middle of the subject and header
lines. Add this to your `.emacs` to replace tabs with spaces in subject
lines:

        (defun notmuch-show-subject-tabs-to-spaces ()
          "Replace tabs with spaces in subject line."
          (goto-char (point-min))
          (when (re-search-forward "^Subject:" nil t)
            (while (re-search-forward "\t" (line-end-position) t)
              (replace-match " " nil nil))))

        (add-hook 'notmuch-show-markup-headers-hook 'notmuch-show-subject-tabs-to-spaces)

And in header lines (this will only work with the yet to be released
notmuch version 0.15):

        (defun notmuch-show-header-tabs-to-spaces ()
          "Replace tabs with spaces in header line."
          (setq header-line-format
                (notmuch-show-strip-re
                 (replace-regexp-in-string "\t" " " (notmuch-show-get-subject)))))

        (add-hook 'notmuch-show-hook 'notmuch-show-header-tabs-to-spaces)

## Hiding unread messages in notmuch-show

I like to have an inbox saved search, but only show unread messages when they
view a thread. This takes two steps:

1. Apply
[this patch from Mark Walters](http://notmuchmail.org/pipermail/notmuch/2012/010817.html)
to add the `notmuch-show-filter-thread` function.
1. Add the following hook to your emacs configuration:

        (defun expand-only-unread-hook () (interactive)
          (let ((unread nil)
                (open (notmuch-show-get-message-ids-for-open-messages)))
            (notmuch-show-mapc (lambda ()
                                 (when (member "unread" (notmuch-show-get-tags))
                                   (setq unread t))))
            (when unread
              (let ((notmuch-show-hook (remove 'expand-only-unread-hook notmuch-show-hook)))
                (notmuch-show-filter-thread "tag:unread")))))

        (add-hook 'notmuch-show-hook 'expand-only-unread-hook)

## Changing the color of a saved search based on some other search

I like to have a saved search for my inbox, but have it change color when there
are thread with unread messages in the inbox. I accomplish this with the
following code in my emacs config:

        (defun color-inbox-if-unread () (interactive)
          (save-excursion
            (goto-char (point-min))
            (let ((cnt (car (process-lines "notmuch" "count" "tag:inbox and tag:unread"))))
              (when (> (string-to-number cnt) 0)
                (save-excursion
                  (when (search-forward "inbox" (point-max) t)
                    (let* ((overlays (overlays-in (match-beginning 0) (match-end 0)))
                           (overlay (car overlays)))
                      (when overlay
                        (overlay-put overlay 'face '((:inherit bold) (:foreground "green")))))))))))
        (add-hook 'notmuch-hello-refresh-hook 'color-inbox-if-unread)

## Linking to notmuch messages and threads from the Circe IRC client

[Circe](https://github.com/jorgenschaefer/circe/wiki) is an IRC client for emacs.
To have clickable buttons for notmuch messages and threads, add the following to
`lui-buttons-list` (using, e.g. M-x customize-variable)

    ("\\(?:id\\|mid\\|thread\\):[0-9A-Za-z][0-9A-Za-z.@-]*" 0 notmuch-show 0)

If you have notmuch-pick installed, it works fine for this as well.