Before you send the heated reply, send one up.

A heated reply feels like precision and is almost always something else. In the minute after you read something unfair, your case is fully assembled and utterly convincing, which is exactly when you are least able to judge it. Putting a pause between the feeling and the sending is not weakness. It is the difference between responding and reacting.

Write the angry version if you need to, then leave it unsent for an hour. Use the delay to ask what you actually want to happen next with this person. Most of the time you will send something shorter, and you will never once wish you had sent the first draft.