How to use yasnippets to produce email templates in Emacs

I publicize my .emacs.d at github. But email templates are my private stuff. So I place them in different location.

That's why I place templates at ~/my-yasnippets/message-mode/.

Here is a sample template to reply my agents (jobok.yasnippet):

# -*- mode: snippet -*-
# name: email for OK job
# key: jobok
# --
Hi ${1:`(my-yas-get-first-name-from-to-field)`},

Thank you very much for providing me this great opportunity.

Unfortunately I'm occupied now and will not consider new job for the time being.

Currently I'm working for ${2:COMPANY_NAME} as a contract developer. However, the
contract will be over ${3:END_OF_CONTRACT} and I will be available then.

So keep in touch.

Attached is my latest CV.
$0

<#part type="application/msword" filename="~/org/cv/cv.doc" disposition=attachment description=resume>
<#/part>

`(my-yas-get-first-name-from-to-field)` is a Lisp function embedded in the snippet.

It will automatically fetch the first name of agent,

(defun my-yas-get-first-name-from-to-field ()
  (let ((rlt "AGENT_NAME") str)
    (save-excursion
      (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))))
    (if (string-match "^To: \"\\([^ ,]+\\)" str)
        (setq rlt (match-string 1 str)))
    (message "rlt=%s" rlt)
    rlt))

Add following code into .emacs to make yasnippet load the emacs templates:

(require 'yasnippet)
(setq my-yasnippets (expand-file-name "~/my-yasnippets"))
(if (and  (file-exists-p my-yasnippets) (not (member my-yasnippets yas-snippet-dirs)))
    (add-to-list 'yas-snippet-dirs my-yasnippets))
;; yasnippet setup code should be AFTER
(yas-global-mode 1)