I may not get your question properly. If you want to hide your reply, then why you will reply in first place? May you please elaborate your question a little so that i can better answer you if my above answer is wrong?
I figure out the way to reply to customer indivudually.
But I hope to know if it’s possible to build some email groups, rather than group message.
Thus customers don’t need to join the group at the beginning.
Same as Gmail will lable the address book.