Change smtp server based on from field

See MSMTP Home Page.

;; Select the correct smtp server based on the from address.
(defun msmtp-account (&optional def)
  (let* ((from
          (save-restriction    
            (message-narrow-to-headers)
            (message-fetch-field "From")))
         (account (if from (catch 'match
                             (dolist (element msmtp-name-list)
                               ;; (message (format "smpt chosen is %s" element))
                               (when (string-match (format ".*%s.*" element) from)
                                 (throw 'match element)))) nil)))
    (if account account (if def def "default"))))

(defun msmtp-change-smtp ()
  (setq sendmail-program "/usr/bin/msmtp")
  (setq smtpmail-starttls-credentials '(("smtp.googlemail.com" 587 nil nil)))
  (setq smtpmail-smtp-server "smtp.googlemail.com")
  (setq message-sendmail-envelope-from 'header)
  (if (message-mail-p)
      (setq message-sendmail-extra-arguments (list "-a" (msmtp-account "default")))))    
(add-hook 'message-send-hook 'msmtp-change-smtp)

(setq message-required-news-headers
      (remove' Message-ID message-required-news-headers))