(if (not (looking-at notmuch-show-message-begin-regexp))
(re-search-backward notmuch-show-message-begin-regexp))
(re-search-forward notmuch-show-filename-regexp)
(if (not (looking-at notmuch-show-message-begin-regexp))
(re-search-backward notmuch-show-message-begin-regexp))
(re-search-forward notmuch-show-filename-regexp)