mu4e configuration layer

extensions.el

(defvar mu4e-pre-extensions
  '(
    mu4e
    ))

(defun mu4e/init-mu4e ()
  (use-package mu4e
    :init
    (add-to-list 'load-path "/usr/local/share/emacs/site-lisp/mu4e")

    :config
    (progn
      (setq mu4e-mu-binary "/usr/local/bin/mu")
      ;; path to our Maildir directory
      (setq mu4e-maildir "~/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   "/[Gmail].Sent Mail"
            mu4e-drafts-folder "/[Gmail].Drafts"
            mu4e-trash-folder  "/[Gmail].Trash"
            mu4e-refile-folder "/[Gmail].All Mail")

      ;; the maildirs you use frequently; access them with 'j' ('jump')
      (setq mu4e-maildir-shortcuts
            '(("/[Gmail].All Mail"    . ?a)
              ("/INBOX"       . ?i)
              ("/[Gmail].Sent Mail"        . ?s)
              ))
          
      ;; a  list of user's e-mail addresses
      (setq mu4e-user-mail-address-list '("[email protected]"
                                          "[email protected]"))
      ;; how to get mail
      (setq mu4e-get-mail-command "offlineimap"   ;; or fetchmail, or ...
            mu4e-update-interval 300             ;; update every 5 minutes
            )
      (setq mu4e-user-mail-address-regexp
      "torben@erlang-solutions\.com\\|torben.hoffmann@erlang-soultions\.com")
      (setq mu4e-org-contacts-file  "~/org/contacts.org")
      (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)

      (setq mu4e-compose-signature (with-temp-buffer
                                     (insert-file-contents "~/.signature")
                                     (buffer-string)))

      (setq message-signature-file "~/.signature")

      (setq gnutls-min-prime-bits 1024)

      (load "tls")
      ;; smtp mail setting
      (require 'smtpmail)
      (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

       
       smtpmail-debug-info t
       ;; 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  t
       smtpmail-queue-dir  "/Users/th/Maildir/queue/cur")

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

      (setq
       ;; mu4e-use-fancy-chars t
       ;; mu4e-view-prefer-html t
       org-mu4e-convert-to-html t
       mu4e-show-images t
       message-kill-buffer-on-exit t
       mu4e-headers-include-related nil
       mu4e-headers-skip-duplicates t
       mu4e-headers-visible-lines 18)

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

      (setq mu4e-headers-date-format "%Y-%m-%d %H.%M")

      ;; from https://github.com/fgallina/dotemacs/blob/master/init.el
      (defun my:mu4e-toggle-headers-include-related ()
        "Toggle `mu4e-headers-include-related' and refresh."
        (interactive)
        (setq mu4e-headers-include-related
              (not mu4e-headers-include-related))
        (mu4e-headers-rerun-search))

      (define-key 'mu4e-headers-mode-map "o"
        'my:mu4e-toggle-headers-include-related)



      ;; view in browser with aV
      (add-to-list 'mu4e-view-actions
                   '("ViewInBrowser" . mu4e-action-view-in-browser) t)

      ;; use imagemagick if available
      (when (fboundp 'imagemagick-register-types)
        (imagemagick-register-types))

      (setq mu4e-html2text-command "html2text -utf8 -nobs -width 100")


      ;; automatic refiling from http://www.djcbsoftware.nl/code/mu/mu4e/Refiling-message.html

      ;; bookmarks for easy access
      (setq mu4e-bookmarks
            '( ("flag:unread AND NOT flag:trashed"     "Unread messages"      ?u)
               ("maildir:/INBOX" "INBOX" ?i)
               ("maildir:/INBOX and not flag:list" "INBOX-me" ?j)
               ("maildir:/INBOX and flag:replied" "Filable" ?f)
               ("date:today..now and maildir:/INBOX" "Today's messages"     ?t)
               ("maildir:/INBOX and date:7d..now"      "Last 7 days"          ?w)
               ("maildir:/INBOX and date:31d..now"    "Last month"          ?m)
               ("maildir:/erlang-questions" "erlang-questions" ?e)
               ("mime:image/*"                         "Messages with images" ?p)
               ("(maildir:/ActivityStream or maildir:/INBOX or maildir:/Redmine) and from:[email protected]"
                "Redmine"              ?r)
               ("(maildir:/ActivityStream or maildir:/INBOX or maildir:/Github)  and from:github.com" "Github"               ?g)
               ("maildir:/ActivityStream and (not from:github.com) and (not from:[email protected])" "Later"  ?l)
               ("(maildir:/INBOX or maildir:/ActivityStream) and (from:[email protected] or from:[email protected]  or from:[email protected])"
                "Alarms" ?a)
               ))



      ;; printing via mutt
      ;; https://groups.google.com/forum/#!searchin/mu-discuss/print/mu-discuss/WQdwVSluj3w/84jzXGL4AP4J
      (add-to-list 'mu4e-view-actions
                   `("Muttprint" .
                     ,(defun mu4e-action-muttprint (msg)
                        "Print the message using muttprint."
                        (mu4e-view-pipe "muttprint -p Virtual_PDF_Printer")))) 

      ;; compose hook from manual §6.4
      (add-hook 'mu4e-compose-mode-hook
                (defun my-do-compose-stuff ()
                  "My settings for message composition."
                  (set-fill-column 85)
                  (flyspell-mode)
                  (artbollocks-mode)
                  (pabbrev-mode)))

      ;; (add-hook 'mu4e-view-mode-hook
      ;;           (defun my-do-view-stuff ()
      ;;             "My settings for viewing messages."
      ;;             (artbollocks-mode)))


      ;; mailto-compose-mail
      ;; from http://www.emacswiki.org/emacs/MailtoHandler
      (defun mailto-compose-mail (mailto-url)
        "Parse MAILTO-URL and start composing mail."
        (if (and (stringp mailto-url)
                 (string-match "\\`mailto:" mailto-url))
            (progn
              (require 'rfc2368)
              (require 'rfc2047)
              (require 'mailheader)

              (let ((hdr-alist (rfc2368-parse-mailto-url mailto-url))
                    (body "")
                    to subject
                    ;; In addition to To, Subject and Body these headers are
                    ;; allowed:
                    (allowed-xtra-hdrs '(cc bcc in-reply-to)))

                (with-temp-buffer
                  ;; Extract body if it's defined
                  (when (assoc "Body" hdr-alist)
                    (dolist (hdr hdr-alist)
                      (when (equal "Body" (car hdr))
                        (insert (format "%s\n" (cdr hdr)))))
                    (rfc2047-decode-region (point-min) (point-max))
                    (setq body (buffer-substring-no-properties
                                (point-min) (point-max)))
                    (erase-buffer))

                  ;; Extract headers
                  (dolist (hdr hdr-alist)
                    (unless (equal "Body" (car hdr))
                      (insert (format "%s: %s\n" (car hdr) (cdr hdr)))))
                  (rfc2047-decode-region (point-min) (point-max))
                  (goto-char (point-min))
                  (setq hdr-alist (mail-header-extract-no-properties)))

                (setq to (or (cdr (assq 'to hdr-alist)) "")
                      subject (or (cdr (assq 'subject hdr-alist)) "")
                      hdr-alist
                      (remove nil (mapcar
                                   #'(lambda (item)
                                       (when (memq (car item) allowed-xtra-hdrs)
                                         (cons (capitalize (symbol-name (car item)))
                                               (cdr item))))
                                   hdr-alist)))

                (compose-mail to subject hdr-alist nil nil
                              (list (lambda (string)
                                      (insert string))
                                    body))))
          (compose-mail)))


      )
    )
  )  

in my .spacemacs I have

(global-set-key [f5] 'mu4e)

and it gives me this message

command-execute: Symbol's function definition is void: mu4e

Updated the gist with a version that works!
Had to do a defvar mu4e-pre-extensions in my extensions.el file. Then it starts loading. Slight difference from the things that goes into packages.el, but now I now.