Last updated on December 13, 2016

When sending out an email, sometimes we just forgot to attach the attachments. An attachment reminder can largely prevent this: You are asked to confirm whether you have forgotten the attachments if your message body shows that you may need one. However, Emacs by default does not provide such a feature in its mail composing mode message-mode, which is used in email clients such as gnus and mu4e. Here is an attachment reminder based on this comment:

(defun my-message-current-line-cited-p ()
  "Indicate whether the line at point is a cited line."
  (save-match-data
    (string-match (concat "^" message-cite-prefix-regexp)
                  (buffer-substring (line-beginning-position) (line-end-position)))))

(defun my-message-says-attachment-p ()
  "Return t if the message suggests there can be an attachment."
  (save-excursion
    (goto-char (point-min))
    (save-match-data
      (let (search-result)
        (while
            (and (setq search-result (re-search-forward "\\(attach\\|pdf\\|file\\)" nil t))
                 (my-message-current-line-cited-p)))
        search-result))))

(defun my-message-has-attachment-p ()
  "Return t if the message has an attachment."
  (save-excursion
    (goto-char (point-min))
    (save-match-data
      (re-search-forward "<#part" nil t))))

(defun my-message-pre-send-check-attachment ()
  (when (and (my-message-says-attachment-p)
             (not (my-message-has-attachment-p)))
    (unless
        (y-or-n-p "The message suggests that you may want to attach something, but no attachment is found. Send anyway?")
      (error "It seems that an attachment is needed, but none was found. Aborting sending."))))
(add-hook 'message-send-hook 'my-message-pre-send-check-attachment)

If “attach”, “pdf” or “file” are in the message you are sending, a confirmation would be required to confirm the attachments if they are not attached.