Add mail configuration (mu4e)

config.org

@@ -415,3 +415,68 @@ needs to be set up to install them if they aren't already.
   #+begin_src emacs-lisp
     (use-package mingus)
   #+end_src
+
+* Mail
+  Currently using =mu4e= for mail. Not sure whether this is my 'final'
+  set up, I might give =notmuch= a try at some point.
+
+  =mu4e= is a bit annoying as it's bundled along with =mu= rather than
+  being loaded from ELPA or MELPA, so it can't be loaded with
+  =use-package=. Indeed, how to load it depends on how =mu= was
+  packaged. On NixOS at least, =mu4e= gets put in a place where Emacs
+  is able to find it, so it just needs to be =require='d.
+
+  #+begin_src emacs-lisp
+    (require 'mu4e)
+  #+end_src
+
+  I'm /sure/ this will break at some point; when it does, probably
+  makes sense to do something like:
+
+  #+begin_src emacs-lisp :tangle no
+    (let ((uname-output (shell-command-to-string "uname -a")))
+      (cond ((string-match-p "NixOS" uname-output) nil)
+            ...))
+    (require 'mu4e)
+  #+end_src
+
+  To get the correct address by default:
+
+  #+begin_src emacs-lisp
+    (setq user-mail-address "cdo@wip.sh")
+  #+end_src
+
+  And to avoid being tickled:
+
+  #+begin_src emacs-lisp
+    (setq mail-host-address "hactar")
+  #+end_src
+
+** Automatic updating
+   For updating through =mu4e= to actually work, [[help:mu4e-get-mail-command][mu4e-get-mail-command]]
+   needs to be set to =offlineimap=. New mail can be then fetched
+   regularly with [[help:mu4e-update-mail-and-index][mu4e-update-mail-and-index]] using [[help:run-with-timer][run-with-timer]].
+
+   #+begin_src emacs-lisp
+     (setq mu4e-get-mail-command "offlineimap")
+     (run-with-timer 0 120 (lambda ()
+                             (mu4e-update-mail-and-index t)))
+   #+end_src
+
+** Mode-line alert
+   =mu4e-alert= provides a convenient little icon that shows up
+   whenever =mu4e= has unread mail.
+
+   #+begin_src emacs-lisp
+     (use-package mu4e-alert
+       :config
+       (add-hook 'after-init-hook
+                 #'mu4e-alert-enable-mode-line-display))
+   #+end_src
+
+** Sending with =sendmail=
+   I have =msmtp= set up so use that to send mail.
+
+   #+begin_src emacs-lisp
+     (setq send-mail-function 'sendmail-send-it)
+   #+end_src