Please provide a functionality such as NoReplyAll so that it is possible to prevent forwarding of e-mails.
I just got a MacBook with a touch bar. I see a reply-all button but no reply button. Reply-all is the devil and should absolutely always be an intentional choice. I suggest the ability to choose which you want or to have the reply-all function only enabled when pressing a modifier key or something.
Disable "Reply to All" for recipients on BCC list, or otherwise make it very clear to the recipient that they received an email via BCC, and to be careful about replying when there are others that are CC'd. BCC is used so that a sender can conceal that an email has been distributed to certain other parties, but because a recipient can reveal themselves to the CC list if they "Reply to All", this may cause problems for the sender. It may also result in clogging the inbox of people without an interest in what the BCC'd person has to say.