Hello,
What plugin do you use to show the mentioned field?
Our Email builder (Dashboard > XStore > Email Builder) has WC hooks that can be added to mails. In case that plugin gets hooked on one of them then the info will come in the letter – http://prntscr.com/1qhpvv1, http://prntscr.com/1qhpw7x
Contact support of the plugin and ask about what woocommerce hook can be used to show the desired information.
Regards