Mail in Emacs
with mu4e, mbsync, msmtp, mutt_oauth2; on GNU/Linux and macOS

This article is written in the hope that it will be useful, but WITHOUT ANY WARRANTY, to the extent permitted by applicable law.

Copyright (C) 2026 The Author (see footer). Some rights reserved.

Permission is granted to make digital or hard copies of this work for personal or classroom use, provided that copies are not made or distributed for profit, commercial, operational, or administrative advantage. Permission is explicitly denied for any use, inclusion, redistribution, or integration of this article—in whole or in part—by professional support services, help desks, or managed service desks. All other redistribution, reproduction, or commercial use requires prior written permission from the copyright holder and proper attribution.

No part of this article is authored or supported by iSolutions, the University of Southampton IT service.

This article contains descriptions of the use of cryptographic programs. A number of nations restrict the use or export of cryptography. If you are potentially subject to such restrictions, you should seek legal advice before attempting to execute such cryptographic commands.

Unless otherwise noted, the code snippets in this article are free: you can redistribute them and/or modify them under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

The code snippets are distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this article (here). If not, see https://www.gnu.org/licenses/.

Preamble

This article introduces how to set up Emacs as an email client using mu (mail indexer), mbsync (mailbox synchronizer), and msmtp (mail transfer agent).

Authentication is handled by mutt_oauth2 if you have access to your mailbox via SMTP/IMAP, or DavMail if not.

This article might still be helpful if you want to access the University M$ Office 365 (Outlook) email using other message user agents, for example mutt, or if you want to look up University contacts using ldapsearch.

1. Microsoft 365 Authentication

If you are using the University Microsoft 365 account [1], Basic Auth (e.g. standard username/password authentication or app password) has been deprecated. There is a non-zero low chance you can still use basic auth, but for most of us, we have to use OAuth2.

There are two methods to achieve this. If you have IMAP and SMTP access to your mailbox (which is possible with reasonable effort as of publication, by carefully reading the University's knowledge base on adding an email account to various email clients [2] and find out what to do), then you can use mutt_oauth2 to handle the OAuth2 flow. Otherwise, you have to use DavMail to translate standard IMAP and SMTP to Microsoft's proprietary protocols.

1.1. Using mutt_oauth2

This method uses a Python script mutt_oauth2.py from [3] to handle the OAuth2 flow, fetching and refreshing access tokens that mbsync and msmtp can use.

  1. Configure the script

    To use this script one needs to install Python 3 and download the script from [3], and chmod +x the script.

    Edit the script with your favourite text editor and make the following changes.

    • Encryption pipe and decryption pipe

      The script needs a way to encrypt and decrypt the OAuth2 token so that it can be safely stored on your machine. Set ENCRYPTION_PIPE and DECRYPTION_PIPE in the script to be your preferred commands.

      OpenPGP [4] is a widely-used open cryptographic standard with its free implementation GNU Privacy Guard (gpg) [5]. To use gpg, first install gpg (may be called gpg2 or gnupg in your package manager) and its dependencies such as pinentry.

      You may create a new pair of keys for asymmetric encryption, reuse your existing key pairs, or use symmetric encryption. If you wish to create a dedicated key, run

      gpg --generate-key
      

      and then enter Real name and Email address (does not necessarily need to be your real name and real email if you dedicate this key for OAuth token encryption, but you will need these later).

      Replace YOUR_GPG_IDENTITY in the Python script with your USER-ID, i.e., the email or public key ID. For example,

      ENCRYPTION_PIPE = ['gpg', '--encrypt', '--recipient', 'mutt_oauth2@example.local']
      DECRYPTION_PIPE = ['gpg', '--decrypt']
      
    • Client ID and client secret

      The script also needs a Client ID. It will pretend to be the Client Application during authorization. The Client must be approved by the IT administrator before it can be used.

      One can create such a Client and ask the administrator for approval, or use an existing Client ID found on the internet—for example, Mozilla Thunderbird has Client ID 9e5f94bc-e8a4-4e73-b8be-63364c29d753 [6]. There is no indication whether using a Client ID will share your information to that Client.

      Change the 'client_id' under 'microsoft' to your Client ID.

    See also: [7]

  2. Configure SASL XOAUTH2

    The authentication uses SASL, so make sure [8] is installed. It is usually called cyrus-sasl or cyrus-sasl2 in package managers.

    After installing Cyrus SASL, compile and install an XOAUTH2 mechanism plugin [9] for Cyrus SASL.

    git clone https://github.com/moriyoshi/cyrus-sasl-xoauth2.git
    cd cyrus-sasl-xoauth2
    ./autogen.sh
    ./configure
    make
    sudo make install
    

    After that, the command saslpluginviewer | grep XOAUTH2 (or might be pluginviewer depending on your distro) should return some plugins instead of empty.

  3. Run the script

    To authorize, run

    mutt_oauth2.py --authorize /path/to/generate/new/token/file
    

    This will generate the token file. After generating the token file, use the following to retrieve the token in plain text.

    mutt_oauth2.py --authorize /path/to/generated/token/file
    

1.2. Using DavMail

If you cannot use mutt_oauth2, then you have to use DavMail [10], which will start a server locally and translate local IMAP and SMTP requests to the proprietary protocols. This is slower than direct IMAP/SMTP access (via mutt_oauth2).

Download and install DavMail. In DavMail Gateway Settings – Main – Gateway, change Exchange Protocol to O365Modern. Set local POP, IMAP, SMTP, etc. ports.

2. Configure isync (mbsync)

Isync is typically called isync in package managers, although the command is mbsync and the configuration file is .mbsyncrc. If your package manager does not provide the latest version, it is strongly recommended to compile from scratch [11].

Create a configuration file ~/.mbsyncrc with mode 0600.

2.1. Example configuration (XOAUTH2)

IMAPAccount soton
Host outlook.office365.com
User abc1d26@soton.ac.uk
PassCmd "/path/to/mutt_oauth2.py /path/to/token"
TLSType IMAPS
AuthMechs XOAUTH2
Port 993

IMAPStore soton-remote
Account soton

MaildirStore soton-local
Subfolders Verbatim
Path ~/Mail/Soton/
Inbox ~/Mail/Soton/INBOX

Channel soton
Far :soton-remote:
Near :soton-local:
Patterns *
Create Near
Sync All
Expunge Both
SyncState *

2.2. Example configuration (DavMail)

Note that PassCmd should be hardened. CertificateFile is only needed if SSL is enabled in DavMail.

IMAPAccount soton
Host localhost
User abc1d26@soton.ac.uk
PassCmd "cat ~/.password"
TLSType None
AuthMechs LOGIN
CertificateFile ~/davmail.pem
Port 1234

IMAPStore soton-remote
Account soton

MaildirStore soton-local
Subfolders Verbatim
Path ~/Mail/Soton/
Inbox ~/Mail/Soton/INBOX

Channel soton
Far :soton-remote:
Near :soton-local:
Patterns *
Create Near
Sync All
Expunge Both
SyncState *

2.3. Synchronize

Synchronize all of (-a) your local MailDir with

mbsync -a

3. Configure msmtp

Install msmtp from your package manager and create a configuration file ~/.msmtprc with mode 0600.

3.1. Example configuration (XOAUTH2)

defaults
logfile ~/Mail/msmtp.log
tls_trust_file /etc/ssl/certs/ca-bundle.crt

account Soton
auth xoauth2
host outlook.office365.com
port 587
protocol smtp
from your.name@soton.ac.uk
user abc1d26@soton.ac.uk
passwordeval "cat ~/.password"
tls on
tls_starttls on

account default : Soton

3.2. Example configuration (DavMail)

Note that passwordeval should be hardened. tls, tls_starttls and tls_fingerprint is only needed if SSL is enabled in DavMail.

defaults
logfile ~/Mail/msmtp.log
tls_trust_file /etc/ssl/certs/ca-bundle.crt

account Soton
auth login
host localhost
port 5678
protocol smtp
from your.name@soton.ac.uk
user abc1d26@soton.ac.uk
passwordeval "/path/to/mutt_oauth2.py /path/to/tokens"
tls on
tls_starttls on
tls_fingerprint DE:AD:BE:EF:DE:CA:FB:AD:C0:FF:EE:BA:BE:BA:5E:BA:11:FF:FF:FF

account default : Soton

3.3. Test configuration

Test the configuration and print the server information with

msmtp -S

4. Mu

Install (or compile from scratch) mu [12] (might be maildir-utils in your package manager).

Ensure mu4e.el is also installed to the site-lisp directory (GNU/Linux: /usr/local/share/emacs/site-lisp/mu4e/mu4e; macOS via Homebrew: /opt/homebrew/share/emacs/site-lisp/mu4e).

Let mu index the synchronized MailDir and build a database by running

mu init --maildir=~/Mail --my-address=abc1d26@soton.ac.uk
mu index

If you have multiple addresses, use multiple --my-address'es, e.g. mu init --maildir=~/Mail --my-address=abc1d26@soton.ac.uk --my-address=your.name@soton.ac.uk

5. Emacs Configurations for Mu4e

The Emacs Lisp code snippets below should be evaluated when you start Emacs, e.g. by putting them in .emacs or init.el.

Assuming Emacs' default use-package is your package manager, this should have little impact on your Emacs startup time.

5.1. Determine path to mu4e

(defvar my-mu4e-path
  (cond
   ((eq system-type 'gnu/linux)
    "/usr/local/share/emacs/site-lisp/mu4e/mu4e")
   ((eq system-type 'darwin)
    "/opt/homebrew/share/emacs/site-lisp/mu4e"))
  "Path to the mu4e package depending on the OS.")

5.2. Set auth-sources

(setq auth-sources
      (append
       '("~/.authinfo" "~/.authinfo.gpg" "~/.netrc")
       (when (eq system-type 'darwin)
         '(macos-keychain-internet
           macos-keychain-generic))))

It is strongly recommended to use the encrypted authinfo [13] (i.e. ~/.authinfo.gpg) instead of the unencrypted authinfo or netrc to store your password.

See [13] for how to create such a file to store passwords.

5.3. Configure package mu4e

(use-package mu4e
  :load-path my-mu4e-path
  :defer t
  :commands (mu4e)
  :config
  (setq mu4e-mu-binary (executable-find "mu"))

This should be the same as your mbsync configuration and mu init path.

  (setq mu4e-root-maildir "~/Mail")

Depending on how you start Emacs, it may not know the environment variable SASL_PATH (e.g. if started as a systemd service). Your SASL_PATH may differ. Also add a timeout, so that if the machine loses internet connection, a stale mbsync process will be killed.

  (setq mu4e-get-mail-command "SASL_PATH=/usr/local/lib/sasl2 timeout -k 5 1m /usr/local/bin/mbsync -a")

Using mu4e to update email periodically. It is also possible to use a systemd timer as mentioned in [14]. It might also be possible to make use of IMAP4 IDLE command [15] and let the server notify an IMAP IDLE client, but Microsoft IMAP server may not honor this.

  (setq mu4e-update-interval 60)

Receiving notifications from Emacs.

  (setq mu4e-notification-support t)
  (mu4e-alert-enable-notifications)

I don't like mu4e-modeline.

  (mu4e-modeline-mode -1)
  (setq mu4e-modeline-mode nil)
  (setq mu4e-modeline-show-global nil)

Depending on how you manage windows, you can change how mu4e splits the view when viewing an article.

  (setq mu4e-split-view 'vertical)
  (setq mu4e-attachment-dir "~/Downloads")
  (setq mu4e-change-filenames-when-moving t)

Add more if you have more accounts. Your inbox should be INBOX. If using Microsoft IMAP without DavMail, then some directories will contain a space, such as 'Conversation History', 'Deleted Items', 'Junk Email', 'RSS Feeds', 'Sent Items' and 'Sync Issues'.

  (setq mu4e-maildir-shortcuts
          '(("/Soton/INBOX" . ?s)
            ("/Soton/Drafts" . ?p)
            ("/Soton/Sent Items" . ?f)
            ("/Soton/Junk Email" . ?j)))
  (setq mu4e-bookmarks
        `((:name  "Unread messages"

A fancy query to omit boring emails in the unread count.

                  :query "flag:unread AND NOT flag:trashed AND NOT maildir:/Soton/Lists/ArXiv AND NOT maildir:/Soton/Deleted* AND NOT mime:application/ics"
                  :key ?u)
          (:name  "Today's messages"
                  :query "date:today..now AND NOT maildir:/Soton/Lists/ArXiv"
                  :key ?t)
          (:name  "Last 7 days"
                  :query "date:7d..now"
                  :key ?w)
          (:name  "Flagged messages"
                  :query "flag:flagged"
                  :key ?i)))

Add more contexts if you have more accounts.

  (setq mu4e-contexts
        `(,(make-mu4e-context
            :name "Soton"
            :enter-func
            (lambda () (mu4e-message "Enter abc1d26@soton.ac.uk context"))
            :leave-func
            (lambda () (mu4e-message "Leave abc1d26@soton.ac.uk context"))
            :match-func
            (lambda (msg)
              (when msg
                (mu4e-message-contact-field-matches msg
                                                    :to "My.Name@soton.ac.uk")))
            :vars '((user-mail-address . "My.Name@soton.ac.uk")
                    (user-full-name . "My Name")
                    (mu4e-drafts-folder . "/Soton/Drafts")
                    (mu4e-refile-folder . "/Soton/Archive")
                    (mu4e-sent-folder . "/Soton/Sent Items")
                    (mu4e-trash-folder . "/Soton/Deleted Items")))))

The default ones if you have more accounts.

  (setq user-mail-address "My.Name@soton.ac.uk")
  (setq user-full-name  "My Name")
  (setq mu4e-drafts-folder "/Soton/Drafts")
  (setq mu4e-refile-folder "/Soton/Archive")
  (setq mu4e-sent-folder "/Soton/Sent Items")
  (setq mu4e-trash-folder "/Soton/Deleted Items")
  (setq mu4e-context-policy 'pick-first)
  (setq mu4e-hide-index-messages t)
  (require 'epa-file)
  (epa-file-enable)
  (setq epg-pinentry-mode 'loopback)
  (setq message-kill-buffer-on-exit t)
  (setq send-mail-function 'sendmail-send-it
        message-send-mail-function 'sendmail-send-it)
  (setq sendmail-program (executable-find "msmtp"))
  (setq mail-specify-envelope-from t)
  (setq message-sendmail-envelope-from 'header)
  (setq message-mail-user-agent t)

See [16] for this defun. If you have multiple accounts, set the correct account before sending emails.

  (defun timu/set-msmtp-account ()
    (if (message-mail-p)
        (save-excursion
          (let*
              ((from (save-restriction
                       (message-narrow-to-headers)
                       (message-fetch-field "from")))
               (account
                (cond
                 ((string-match "My.Name@soton.ac.uk" from) "Soton")
                 ((string-match "myname1@acm.org" from) "ACM"))))
            (message "Set msmtp account to: %s" account)
            (setq message-sendmail-extra-arguments (list "-a" account))))))
  (add-hook 'message-send-hook 'timu/set-msmtp-account)

On 31 Feb 2026, at 12:34:56 GMT, Some One <some.one@soton.ac.uk> wrote:

  (setq message-citation-line-format "On %d %b %Y, at %H:%M:%S %Z, %f wrote:\n")
  (setq message-citation-line-function 'message-insert-formatted-citation-line)

Signature (separated with "-​-​ ​").

  (setq message-signature
        (concat
         "My Name\n"
         "University of Southampton\n"
         "https://www.southampton.ac.uk/~qs2g22\n"))

Always BCC myself.

  (add-hook 'mu4e-compose-mode-hook
            (lambda ()
              (save-excursion
                (message-add-header "BCC: My.Name@soton.ac.uk\n")

Format User-Agent. If using DavMail, User-Agent will be lost and you should also include X-Mailer.

                (message-add-header
                 (format "User-Agent: mu4e/%s Emacs/%s"
                         mu4e-mu-version
                         emacs-version))
                (message-add-header
                 (format "X-Mailer: mu4e/%s Emacs/%s"
                         mu4e-mu-version
                         emacs-version)))))
  (setq mu4e-user-agent-string (format "mu4e/%s Emacs/%s"
                                       mu4e-mu-version
                                       emacs-version)))

5.4. Alert in Emacs

(use-package alert
  :init
  (cond
   ((eq system-type 'darwin)
    (setq alert-default-style 'osx-notifier))
   ((eq system-type 'gnu/linux)
    (setq alert-default-style 'notifications))))

(use-package mu4e-alert
  :ensure t
  :defer t
  :after mu4e
  :config
  (cond
   ((eq system-type 'darwin)
    (setq mu4e-alert-set-default-style 'osx-notifier))
   ((eq system-type 'gnu/linux)
    (setq mu4e-alert-set-default-style 'notifications)))
  (setq mu4e-alert-email-notification-types '(count subjects))
  (mu4e-alert-enable-notifications)
  (setq mu4e-alert-interesting-mail-query "flag:unread AND NOT flag:trashed AND NOT maildir:/Soton/Lists/ArXiv AND NOT maildir:/Soton/Deleted* AND NOT mime:application/ics"))

5.5. Move point to beginning of line

If you set mu4e-split-view to non-nil, you may find that if the point is not at the beginning of a line when you hit enter to view an article in mu4e-header, the header view will unexpectedly move right after an mu4e-article is open. Use this mode map to reset the point when navigating the mu4e-header with a mouse.

(with-eval-after-load 'mu4e-headers
  (defun qs2g22/mu4e-headers-mouse-set-point-and-bol (event)
    "Move point to the clicked position, then move to beginning of line.
Argument EVENT is the mouse event."
    (interactive "e")
    (mouse-set-point event)
    (move-beginning-of-line nil))
  (define-key mu4e-headers-mode-map [mouse-1] 
              #'qs2g22/mu4e-headers-mouse-set-point-and-bol))

5.6. Using mu4e

  • To start mu4e, M-x mu4e.
  • You can j ump to a maildir, or visit a b ookmark.
  • You can also s earch for an email.
  • When viewing an article, you can R eply, reply to all (W) or F orward it.
  • You can also C ompose a new one, send it with C-c C-c, postpone (don't send) it with C-c C-d or kill it with C-c C-k. You can drag and drop attachments, or attach a file with:

    <#part type="mime/type" filename="/path/to/file" disposition=attachment>
    <#/part>
    

References

[1]
iSolutions, “Your it essentials.” [Online]. Available: https://www.southampton.ac.uk/isolutions/itessentials.page
[2]
M. Cattelan, “How to add or remove an email account to microsoft outlook.” [Online]. Available: https://sotonproduction.service-now.com/serviceportal?id=kb_article_view&sysparm_article=KB0081901
[3]
Mutt Project, “mutt_oauth2.py.” [Online]. Available: https://gitlab.com/muttmua/mutt/-/blob/master/contrib/mutt_oauth2.py
[4]
P. Wouters, D. Huigens, J. Winter, and Y. Niibe, “OpenPGP,” 2024, RFC 9580; RFC Editor: 9580. doi: 10.17487/RFC9580.
[5]
GnuPG, “The GNU privacy guard.” [Online]. Available: https://www.gnupg.org/
[6]
Thunderbird, “Microsoft OAuth authentication and Thunderbird in 2026.” [Online]. Available: https://support.mozilla.org/en-US/kb/microsoft-oauth-authentication-and-thunderbird-202
[7]
D. Jacob, “Configure Mutt to work with OAuth 2.0.” [Online]. Available: https://www.dcs.gla.ac.uk/~jacobd/posts/2022/03/configure-mutt-to-work-with-oauth-20/
[8]
Cyrus SASL, “Installation.” [Online]. Available: https://www.cyrusimap.org/sasl/sasl/installation.html
[9]
M. Koizumi, “cyrus-sasl-xoauth2.” [Online]. Available: https://github.com/moriyoshi/cyrus-sasl-xoauth2
[10]
M. Guessant, “DavMail gateway.” [Online]. Available: https://davmail.sourceforge.net/
[11]
isync, “Isync: free IMAP and MailDir mailbox synchronizer.” [Online]. Available: https://isync.sourceforge.io/
[12]
D.-J. C. Binnema, “Welcome to mu!” [Online]. Available: https://www.djcbsoftware.nl/code/mu/
[13]
Free Software Foundation, “Emacs auth-source library 0.3.” [Online]. Available: https://www.southampton.ac.uk/~qs2g22/mirror/info/misc/auth.html
[14]
[15]
B. Leiba, “IMAP4 IDLE command,” 1997, RFC 2177; RFC Editor: 2177. doi: 10.17487/RFC2177.
[16]
A. Bertrand, “Email setup in emacs with mu4e on macos.” [Online]. Available: https://macowners.club/posts/email-emacs-mu4e-macos/
[17]
The OpenLDAP Project, “OpenLDAP.” [Online]. Available: https://www.openldap.org/
[18]
Free Software Foundation, “Emacs unified directory client (EUDC) manual.” [Online]. Available: https://www.southampton.ac.uk/~qs2g22/mirror/info/misc/eudc.html
[19]
J. Zawinski, “HTML email, was that your fault?” [Online]. Available: https://www.jwz.org/blog/2017/09/html-email-was-that-your-fault/
[20]
Free Software Foundation, “27.14.1 Enriched mode.” [Online]. Available: https://www.southampton.ac.uk/~qs2g22/mirror/info/emacs/Enriched-Mode.html
[21]
J. Kitchin, “Sending html emails from org-mode with org-mime.” [Online]. Available: https://kitchingroup.cheme.cmu.edu/blog/category/email/
[22]
Q. Sun, “authinfo-utils: Authinfo utility suite.” [Online]. Available: https://git.soton.ac.uk/qs2g22/authinfo-utils

Appendix

A. LDAP Search

To automatic-complete University of Southampton LDAP contacts on Tab, configure ldapsearch [17] and eudc [18].

  • Configure ldapsearch

    Edit ~/.ldaprc.

    URI ldaps://nlbldap.soton.ac.uk
    BASE OU=User,DC=soton,DC=ac,DC=uk
    BINDDN abc1d26@soton.ac.uk
    

    Run the following and enter your University password, where "abc1d2*" is your University username with wildcard.

    ldapsearch -x -W "(cn=abc1d2*)"
    

    You should see your LDAP contact details. It can be easily shown that Kerberos is a better approach than simple password authentication, and such a trivial Kerberos set-up is left as an exercise for the reader.

  • Configure Emacs

    Make sure to add your LDAP username and password to ~/.authinfo.gpg or equivalent, so that Emacs will know your password.

    (with-eval-after-load "message"
      (define-key message-mode-map (kbd "TAB") 'eudc-expand-try-all))
    (setopt eudc-server-hotlist
            '(("" . bbdb)
              ("ldaps://nlbldap.soton.ac.uk" . ldap)))
    (with-eval-after-load 'eudc
      (eudc-set-server "ldaps://nlbldap.soton.ac.uk" 'ldap t))
    (setopt ldap-host-parameters-alist
            '(("ldaps://nlbldap.soton.ac.uk"
               base "OU=User,DC=soton,DC=ac,DC=uk"
               binddn "abc1d26@soton.ac.uk"
               auth simple
               auth-source t)))
    (setq ldap-default-host "ldaps://nlbldap.soton.ac.uk")
    
    (add-to-list 'company-backends 'company-eudc)
    
    (setq eudc-server "ldaps://nlbldap.soton.ac.uk")
    (setq eudc-strict-return-matches nil)
    
    (setq eudc-inline-query-format '((name)
                                     (givenName)
                                     (cn)
                                     (mail)
                                     (displayName)))
    

    Go to a buffer e.g. *scratch*, type a partial email address, then M-x eudc-expand-inline. This should complete the email address.

    If this works, compose an email in mu4e, and Tab should work to auto-complete email addresses.

    If you only need to search for someone without composing an email, use M-x eudc-query-form.

B. RSS Feed with Newsticker

Did you know that you can receive updates from https://moodle.ecs.soton.ac.uk via RSS?

(use-package newsticker
  :ensure nil
  :config
  (setq newsticker-url-list
        '(("COMP1234 Announce" "https://moodle.ecs.soton.ac.uk/rss/file.php/***/***/mod_forum/***/rss.xml")
          ("ELEC5678 Announce" "https://moodle.ecs.soton.ac.uk/rss/file.php/***/***/mod_forum/***/rss.xml"))))

C. HTML Emails

  • First MUAs to render HTML emails? [19]
  • What about Enriched-Mode (text/enriched)? [20]
  • Some emails might be sent in TNEF (maybe because of DavMail?)

    Content-Type: application/ms-tnef; name="winmail.dat"
    
  • org-msg might work.

    (use-package org-msg
      :after mu4e
      :defer t
      :config
      (define-key org-msg-edit-mode-map (kbd "TAB") #'org-msg-tab)
      (define-key org-msg-edit-mode-map (kbd "C-c C-a") #'+mu4e/attach-files)
      (defvar +mu4e-compose-org-msg-toggle-next t)
      (setq org-msg-convert-citation t)
      (setq org-msg-signature "
    
      #+begin_signature
      @@html:&#45;&#45;@@ @@html:<br />@@
      @@html:<b>@@My Name@@html:</b><br />@@
      University of Southampton@@html:<br />@@
      [[https://www.southampton.ac.uk/~qs2g22/]]@@html:<br />@@
      @@html:<small>@@ /Email composed using [[https://www.gnu.org/software/emacs/][Emacs]] [[https://orgmode.org/][Org mode]], sent using mu4e./ @@html:</small>@@
      #+end_signature")
      (advice-add 'org-msg-preview :around
                  (lambda (orig-fun &rest args)
                    (let ((browse-url-browser-function #'browse-url-default-browser))
                      (apply orig-fun args))))
      (defun +mu4e-draft-open-signature-a (fn &rest args)
        "Prevent `mu4e-compose-signature' from being used with `org-msg-mode'."
        (let ((mu4e-compose-signature (unless org-msg-mode mu4e-compose-signature)))
          (apply fn args)))
      (advice-add 'mu4e-draft-open :around #'+mu4e-draft-open-signature-a)
      (org-msg-mode))
    
  • See also Kitchin's blogs on sending HTML emails: [21]

D. Password Lookup

It is possible to write a defun and ask Emacs for password (auth-source-search).

A more secure implementation by the Author adds a list of pluggable authentication modules before giving out the password, available at [22].

E. IMAP IDLE Client

If your IMAP server accepts the IDLE command (e.g. DavMail), then you can write a bash script to let the IMAP server notify you when there is a new mail.

Assuming the connection to the server is encrypted (so we use openssl).

You should review the code and adapt it to your IMAP server (e.g. by testing it with interactive openssl commands first) before executing it.

#!/bin/bash

# Copyright (C) 2026  Qiyang Sun

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see https://www.gnu.org/licenses/.


IMAP_SERVER="localhost"
IMAP_PORT="993"
USERNAME="abc1d26@soton.ac.uk"
PASSWORD=$(cat ~/.password)

IDLE_TIMEOUT=1740
LAST_EXISTS=0

notify_new_mail() {
    notify-send "IMAP IDLE Notify" "New mail in INBOX." --icon=mail-unread
    mbsync -a
}

cleanup() {
    echo "exiting..."
    kill $COPROC_PID 2>/dev/null
    wait
    exit 1
}

trap cleanup SIGINT SIGTERM

echo -n "connecting to $IMAP_SERVER:$IMAP_PORT... "

coproc IMAP { openssl s_client -connect "$IMAP_SERVER:$IMAP_PORT" -quiet; }

if [ -z "$IMAP_PID" ]; then
    echo "FAILED"
    echo "Failed to start openssl."
    exit 1
fi

read -r -t 5 greeting <&"${IMAP[0]}"
if [[ ! "$greeting" == *"OK"* ]]; then
    echo "FAILED"
    echo "$greeting"
    cleanup
fi

echo "done."
echo "connection is now encrypted."
echo "greeting: $greeting"

echo -n "authenticating with LOGIN \"$USERNAME\" \"******\"... "
echo "A1 LOGIN \"$USERNAME\" \"$PASSWORD\"" >&"${IMAP[1]}"
read -r -t 5 response <&"${IMAP[0]}"
if [[ "$response" == *"NO"* ]] || [[ "$response" == *"BAD"* ]]; then
    echo "FAILED"
    echo "$response"
    cleanup
fi
echo "done."

echo -n "selecting INBOX... "
echo "A2 SELECT INBOX" >&"${IMAP[1]}"
while read -r -t 5 response <&"${IMAP[0]}"; do
    if [[ "$response" =~ ^\*[[:space:]]+([0-9]+)[[:space:]]EXISTS ]]; then
        LAST_EXISTS=${BASH_REMATCH[1]}
    fi
    if [[ "$response" == *"A2 OK"* ]]; then
        break
    fi
done
echo "done. (Initial count: $LAST_EXISTS)"

while true; do
    echo -n "entering IDLE mode... "
    echo "A3 IDLE" >&"${IMAP[1]}"
    read -r -t 30 response <&"${IMAP[0]}"
    if [[ "$response" != *"+"* ]]; then
        echo "FAILED"
        echo "response is: $response"
        echo "imap0 is: ${IMAP[0]}"
        cleanup
    fi
    echo "done."

    while read -r -t "$IDLE_TIMEOUT" response <&"${IMAP[0]}"; do
        response=$(echo "$response" | tr -d '\r')
        echo "server: $response"

        if [[ "$response" =~ ^\*[[:space:]]+([0-9]+)[[:space:]]EXISTS ]]; then
            CURRENT_EXISTS=${BASH_REMATCH[1]}

            if (( CURRENT_EXISTS > LAST_EXISTS )); then
                echo "New mail detected! ($LAST_EXISTS -> $CURRENT_EXISTS)"
                notify_new_mail
                LAST_EXISTS=$CURRENT_EXISTS
            else
                echo "EXISTS update received ($CURRENT_EXISTS), but count not incremented."
            fi
        fi
    done

    if [ $? -gt 128 ]; then
        echo "IDLE timed out."
    else
        echo "Connection lost."
        cleanup
    fi

    echo "sending DONE."
    echo "DONE" >&"${IMAP[1]}"
    sleep 2
done

F. GNU General Public License

                    GNU GENERAL PUBLIC LICENSE
                       Version 3, 29 June 2007

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 Everyone is permitted to copy and distribute verbatim copies
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parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work
conveyed by you (or copies made from those copies), or (b) primarily
for and in connection with specific products or compilations that
contain the covered work, unless you entered into that arrangement,
or that patent license was granted, prior to 28 March 2007.

  Nothing in this License shall be construed as excluding or limiting
any implied license or other defenses to infringement that may
otherwise be available to you under applicable patent law.

  12. No Surrender of Others' Freedom.

  If conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot convey a
covered work so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you may
not convey it at all.  For example, if you agree to terms that obligate you
to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this
License would be to refrain entirely from conveying the Program.

  13. Use with the GNU Affero General Public License.

  Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU Affero General Public License into a single
combined work, and to convey the resulting work.  The terms of this
License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License,
section 13, concerning interaction through a network will apply to the
combination as such.

  14. Revised Versions of this License.

  The Free Software Foundation may publish revised and/or new versions of
the GNU General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

  Each version is given a distinguishing version number.  If the
Program specifies that a certain numbered version of the GNU General
Public License "or any later version" applies to it, you have the
option of following the terms and conditions either of that numbered
version or of any later version published by the Free Software
Foundation.  If the Program does not specify a version number of the
GNU General Public License, you may choose any version ever published
by the Free Software Foundation.

  If the Program specifies that a proxy can decide which future
versions of the GNU General Public License can be used, that proxy's
public statement of acceptance of a version permanently authorizes you
to choose that version for the Program.

  Later license versions may give you additional or different
permissions.  However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
later version.

  15. Disclaimer of Warranty.

  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

  If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely approximates
an absolute waiver of all civil liability in connection with the
Program, unless a warranty or assumption of liability accompanies a
copy of the Program in return for a fee.

                     END OF TERMS AND CONDITIONS

            How to Apply These Terms to Your New Programs

  If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

  To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.

Also add information on how to contact you by electronic and paper mail.

  If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

    <program>  Copyright (C) <year>  <name of author>
    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License.  Of course, your program's commands
might be different; for a GUI interface, you would use an "about box".

  You should also get your employer (if you work as a programmer) or school,
if any, to sign a "copyright disclaimer" for the program, if necessary.
For more information on this, and how to apply and follow the GNU GPL, see
<https://www.gnu.org/licenses/>.

  The GNU General Public License does not permit incorporating your program
into proprietary programs.  If your program is a subroutine library, you
may consider it more useful to permit linking proprietary applications with
the library.  If this is what you want to do, use the GNU Lesser General
Public License instead of this License.  But first, please read
<https://www.gnu.org/licenses/why-not-lgpl.html>.


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