;; See: https://www.gnu.org/software/emacs/manual/html_node/emacs-mime/Display-Customization.html#Display-Customization
(setq
 gnus-inhibit-images t
 mm-html-inhibit-images t
 mm-enable-external 'ask
 mm-discouraged-alternatives '("text/html" "text/richtext" "text/enriched" "image/.*")
 mailcap-download-directory "/tmp")

;; See: https://github.com/emacs-mirror/emacs/commit/befa9fcaae29a6c9a283ba371c3c5234c7f644eb

;; Gnus ignores `mm-automatic-display' for text/ derived MIME types, this is not mentioned
;; in the docstring. Ideally, Gnus would default to dumb display of inline text and allow
;; the user to explicitly enable fancy MIME-based major-mode auto-triggering / fontification.
;; The default fail-open model that turns any unexpected evaluation bug into a remote exploit
;; triggered by the user simply opening an email is a disaster.

;; This is the only way I found to stop Gnus from enabling major modes on arbitrary input.
;; I'm keeping text/plain, text/html and disabling everything else.
;; TODO: Write my own `mm-inline-text' replacement.
(setq
 mm-automatic-display '("text/plain")
 mm-inlined-types '("text/plain" "text/html")
 mm-inline-media-tests
 `(("text/plain" mm-inline-text identity)
   ("text/html"
    mm-inline-text-html
    ,(lambda (_handle)
       mm-text-html-renderer))
   (".*" ignore identity)))

;; Show buttonized UI elements for PGP signed messages
(setq gnus-buttonized-mime-types
      '("multipart/alternative" "multipart/encrypted" "multipart/signed" ".*/signed"
        "text/x-org" "text/richtext" "text/enriched"))