Reply All in Mail still works after you've started typing the reply

finermac:

When replying to an email sent to multiple persons, you can select “Reply” to reply only to the sender, or “Reply All” to CC everyone else as well. If you do a Reply and then start typing away, you can still select Reply All from the message’s toolbar to do a Reply All without having to start over—Apple Mail will simply add the other email recipients to the CC field.