Customise the reply quote string in mu4e

You know the bit of text that appears before the quoted email when you reply to someone? Of course you can customise this in mu4e. By default a quoted reply will be preceded with something like

"On Mon, 30 Jan 2017, Joe Bloggs wrote:"

I wanted to include the time and email address of the sender, so I customised the variable message-citation-line-format as follows

;; customize the reply-quote-string
(setq message-citation-line-format "On %a %d %b %Y at %R, %f wrote:\n")
;; choose to use the formatted string
(setq message-citation-line-function 'message-insert-formatted-citation-line)

which translates to something like this

On Mon 30 Jan 2017 at 19:17, Joe Bloggs <> wrote:

The formatting options can be found by looking up the help for the variable with C-h v message-citation-line-format.

Sadly, this change broke my function to extract the sender name for my email template. Here is an updated version:

;; function to return first name of email recipients
;; used by yasnippet
;; inspired by
(defun bjm/mu4e-get-names-for-yasnippet ()
  "Return comma separated string of names for an email"
  (let ((email-name "") str email-string email-list email-name2 tmpname)
      (goto-char (point-min))
      ;; first line in email could be some hidden line containing NO to field
      (setq str (buffer-substring-no-properties (point-min) (point-max))))
    ;; take name from TO field - match series of names
    (when (string-match "^To: \"?\\(.+\\)" str)
      (setq email-string (match-string 1 str)))
    ;;split to list by comma
    (setq email-list (split-string email-string " *, *"))
    ;;loop over emails
    (dolist (tmpstr email-list)
      ;;get first word of email string
      (setq tmpname (car (split-string tmpstr " ")))
      ;;remove whitespace or ""
      (setq tmpname (replace-regexp-in-string "[ \"]" "" tmpname))
      ;;join to string
      (setq email-name
            (concat email-name ", " tmpname)))
    ;;remove initial comma
    (setq email-name (replace-regexp-in-string "^, " "" email-name))

    ;;see if we want to use the name in the FROM field
    ;;get name in FROM field if available, but only if there is only
    ;;one name in TO field
    (if (< (length email-list) 2)
        (when (string-match "^On.+, \\([^ ,\n]+\\).+wrote:$" str)
            (setq email-name2 (match-string 1 str))
            ;;prefer name in FROM field if TO field has "@"
            (when (string-match "@" email-name)
              (setq email-name email-name2))