Open links at point with ‘RET’.
(with-eval-after-load 'notmuch
(defun my-notmuch-show-browse-url-or-toggle-message ()
(interactive)
(if (thing-at-point 'url)
(goto-address-at-point)
(notmuch-show-toggle-message))))
(with-eval-after-load 'notmuch
(keymap-set notmuch-show-mode-map
"RET"
#'my-notmuch-show-browse-url-or-toggle-message))