The Final Result

Let me start this article by showing you the final result of this article. Below you see a screengrab of me

  • checking the new mails I received today, from across 3 separate mail accounts (including a gmail account)
  • deleting two mails on the fly, while skimming the remaining two
  • searching through all my mails for the keywords "thalia AND FIFA" and finding the result immediately

Everything is done within Emacs, no context switching or anything else needed. In this post, I'll describe my set-up as minimalistically as possible.

Setting up the framework

Mu

First, you need to install Mu from the sources, which works as a indexing and search engine on your offline email cache. On Ubuntu 20.04, this consists in extracting the sources, and running

./configure

within the extracted folder. For my setup, I additionally needed to install three dependencies for the configuration to cleanly run through:

sudo apt install libgtk2.0-dev libgmime-3.0-dev libxapian-dev

After this, a simple

make
make install

installed mu.

Encrypting passwords etc.

In what follows, this file will require numerous sensitive data entries, such as passwords, tokens etc. In order to avoid storing these entries in plain text, I follow this stackexchange answer but add a few tweaks. First, if not already existing, create a gpg key via

gpg --full-generate-key

Next, download and install pass and set it up by

pass init "Name of your GPG key"

With this setup, encrypting any type of information is as simple as

pass insert foo/bar

and the prompt will ask you for it, and store it in the given file destination.

Next, save the following python script as something like ~/.offlineimap.py :

import os
import subprocess

def mailpasswd(acct):
  acct = os.path.basename(acct)
  path = "/home/<username>/.passwd/%s.gpg" % acct
  args = ["gpg", "--use-agent", "--quiet", "--batch", "-d", path]
  try:
    return subprocess.check_output(args).strip()
  except subprocess.CalledProcessError:
    return ""

def prime_gpg_agent():
  ret = False
  i = 1
  while not ret:
    ret = (mailpasswd("prime") == "prime")
    if i > 2:
      from offlineimap.ui import getglobalui
      sys.stderr.write("Error reading in passwords. Terminating.\n")
      getglobalui().terminate()
    i += 1
  return ret

prime_gpg_agent()

change <username> accordingly.

Setting up offlineimap

Offlineimap is already pre-installed in Ubuntu, so the only "setting up" to do is the configuration of the aptly named file ~/.offlineimaprc.

Automatic start with the system

In order for offlineimap to simply run in the background instead of starting it manually, the service needs to be registered in systemctl. First, the appropriate unit files, which can be found in the source code in the folder /contrib/systemd/ need to be copied to /usr/lib/systemd/user, the daemon can then be started via

systemctl --user enable offlineimap.service

GMail

For GMail, the necessary encryption standards have improved in recent times, and Gmail no longer likes the encryption provided by sending the user/password combination directly (via remoteuser and remotepasseval). Rather, it expects communication via XOAUTH2. Hence, following the official documentation, I created and received my oauth2_client_id and oauth2_client_secret from Google. After that, further following the official documentation, I cloned the gmail-oauth2-tools repo and created the oauth2_token as described, using

python python/oauth2.py --generate_oauth2_token \
            --client_id=YOUR_CLIENT_ID --client_secret=YOUR_CLIENT_SECRET

This generated both an access token and a refresh token, both of which I put into encrypted files, as described above. I finalized the offlineimaprc setup, it now looks like this, including one other account that uses basic password security:

[general]
accounts = gmail, sastibe
maxsyncaccounts = 2
pythonfile = ~/.offlineimap.py


[Account gmail]
localrepository = LocalGmail
remoterepository = RemoteGmail
autorefresh = 5
quick = 10
postsynchook = mu index --maildir ~/Mails

[Repository LocalGmail]
type = Maildir
localfolders = ~/Mails/gmail

[Repository RemoteGmail]
type = Gmail
maxconnections = 2
remoteuser = sebastian.a.schweer@gmail.com
oauth2_request_url = https://accounts.google.com/o/oauth2/token

oauth2_client_id_eval = mailpasswd("gmail_oauth2_client_id")
oauth2_client_secret_eval = mailpasswd("gmail_oauth2_client_secret")
oauth2_refresh_token_eval = mailpasswd("gmail_oauth2_refresh_token")

folderfilter = lambda foldername: foldername not in ['[Gmail]/All Mail', '[Gmail]/Important']
sslcacertfile = /etc/ssl/certs/ca-certificates.crt


[Account sastibe]
localrepository = Localsastibe
remoterepository = Remotesastibe
autorefresh = 5
quick = 10
postsynchook = mu index --maildir ~/Mails

[Repository Localsastibe]
type = Maildir
localfolders = ~/Mails/sastibe

[Repository Remotesastibe]
type = IMAP
remotehost = imap.1und1.de
ssl = yes
remoteuser = sastibear@sastibe.de
remotepasseval = mailpasswd("sastibe_password")

sslcacertfile = /etc/ssl/certs/ca-certificates.crt

Config for .emacs

Including mu4e

This is fortunately quite simple after the previous installation of mu, just add

(add-to-list 'load-path "/usr/local/share/emacs/site-lisp/mu4e/")
(require 'mu4e)

to your .emacs and you are good to go.

Basic setup

These are the necessary settings for using mu4e with offlineimap and XOAUTH2 encryption:

(require 'smtpmail)
(require 'auth-source-xoauth2)

(setq mail-user-agent 'mu4e-user-agent)
(setq mu4e-sent-messages-behavior 'delete)

(setq message-send-mail-function 'smtpmail-send-it)
(setq mu4e-get-mail-command "offlineimap")
(setq mu4e-headers-date-format "%d-%m-%Y %H:%M")
(setq mu4e-headers-fields '((:human-date . 20)
			    (:flags . 6)
			    (:from . 22)
			    (:maildir . 8)
			    (:subject)))


Encryption for XOAUTH2

For XOAUTH2 communication, GMail expects a specific set of parameters to be transmitted.



(defun my-xoauth2-get-secrets (host user port)
  (when (and (string= host "smtp.gmail.com")
             (string= user "sebastian.a.schweer@gmail.com"))
    (list
     :token-url "https://accounts.google.com/o/oauth2/token"
     :client-id     (auth-source-pass-get 'secret "Email/gmail_oauth2_client_id")
     :client-secret (auth-source-pass-get 'secret "Email/gmail_oauth2_client_secret")
     :refresh-token (auth-source-pass-get 'secret "Email/gmail_oauth2_refresh_token"))))
(setq auth-source-xoauth2-creds 'my-xoauth2-get-secrets)
(add-to-list 'smtpmail-auth-supported 'xoauth2)
(auth-source-xoauth2-enable)
(setq auth-sources (quote (xoauth2 password-store)))

Mu4e Contexts

In order to separate the accounts and keep the commands adjustable, I use mu4e-contexts like so:




(setq mu4e-contexts
 `( ,(make-mu4e-context
     :name "gmail"
     :match-func (lambda (msg) (when msg
       (string-prefix-p "/gmail" (mu4e-message-field msg :maildir))))
     :vars '(
	     (mu4e-refile-folder . "/Gmail/[Gmail].Archive")
	     (mu4e-drafts-folder . "/gmail/[Gmail].Drafts")
	     (mu4e-sent-folder   . "/gmail/[Gmail].Sent Mail")
	     (mu4e-trash-folder  . "/gmail/[Gmail].Trash")
	     (smtpmail-stream-type . ssl)
	     (smtpmail-default-smtp-server . "smtp.gmail.com")
	     (smtpmail-smtp-server  . "smtp.gmail.com")
	     (smtpmail-smtp-service . 465)
	     (smtpmail-smtp-user    . "sebastian.a.schweer@gmail.com")
	     (auth-source-xoauth2-creds . 'my-xoauth2-get-secrets)
       ))
   ,(make-mu4e-context
     :name "sastibe"
     :match-func (lambda (msg) (when msg
       (string-prefix-p "/sastibe" (mu4e-message-field msg :maildir))))
     :vars '(
	     (mu4e-sent-folder   . "/sastibe/Gesendete Objekte")
	     (mu4e-trash-folder  . "/sastibe/Gesendete Objekte")
	     (mu4e-refile-folder . "/sastibe/Spam")
	     (mu4e-drafts-folder . "/sastibe/Entw&APw-rfe")
	     (user-mail-address  . "sastibear@sastibe.de")
	     (smtpmail-default-smtp-server . "smtp.1und1.de")
	     (smtpmail-smtp-user . "sastibear@sastibe.de")
	     (smtpmail-smtp-server . "smtp.1und1.de")
	     (smtpmail-stream-type . starttls)
	     (smtpmail-smtp-service . 587)
     ))
   ))



Debugging

If things don't run as expected, the following settings allow for deeper troubleshooting:

(setq auth-source-debug t)
(setq smtpmail-debug-info t)

Sources & Acknowledgements

Essentially I follow this post from 2017, and adjust it according to my setup (Ubuntu 20.04) as well as new security policies as ordained by Google Mail. I am much indebted to two of the three discussions in the repo for auth-source-pass to figure out the proper way to apply this package.