Don’t answer a long angry message with a longer one. Short and calm ends more fights.

Length reads as escalation regardless of content. A long reply signals that you have been thinking about this for a while, and it gives the other person a dozen new points to respond to, which guarantees another round. A short, calm answer has nothing to grab and nowhere obvious to go next.

When something arrives hot, write whatever you want and then do not send it. Send two or three sentences instead: what you heard, what you will do, and when. Most arguments end there, because there is no fuel left in the reply.