mu4e: Check file instead of symbol existence

.emacs.d/init.el

@@ -165,9 +165,12 @@
   (global-set-key (kbd "C-x g") 'magit-status))
 
 ;;; Mail
-(when (fboundp 'mu4e)
+;; mu4e is usually site-local and not part of ELPA.
+(when (delq nil (mapcar (lambda (path) (string-match "/mu4e/\\|/mu4e$" path)) load-path))
   (nconc package-selected-packages '(helm-mu mu4e-maildirs-extension mu4e-alert)))
 (with-eval-after-load 'mu4e (require 'init-mu4e))
+;; TODO: It seems that calling `mu4e-headers-unread' directly does not initialize mu4e properly:
+;; it won't fetch e-mails and won't complete addresses.
 (autoload 'mu4e-headers-unread "mu4e")
 
 ;;; Makefile

.emacs.d/lisp/init-exwm.el

@@ -80,7 +80,7 @@
 (when (fboundp 'emms)
   (exwm-input-set-key (kbd "s-a") #'emms-smart-browse)
   (exwm-input-set-key (kbd "s-A") #'emms))
-(when (fboundp 'mu4e)
+(when (delq nil (mapcar (lambda (path) (string-match "/mu4e/\\|/mu4e$" path)) load-path))
   (exwm-input-set-key (kbd "s-m") #'mu4e-headers-unread))
 
 ;;; External application shortcuts.