If you must use email, keep the recipient list tight. Only cc (carbon copy) those who need to be aware of what’s being communicated, but not directly participate in the discourse. Deescalate, or make the recipient list shorter, when you need to narrow the conversation. Escalation occurs when, in the course of a thread, you add someone because you realize they should be aware. If doing this as a reply all, add their name to the top of the email so others know they’ve been added, and why. It may be better, though, to forward them the thread along with a note so they can get caught up without having to read the whole thing. Bcc should only be used for newsletters or other cases where you don’t expect a response, never to quietly add someone to the communication. If someone who’s been bcc’d replies all, the gig is up.