Write the angry text. Wait an hour. Read it as the person getting it. Then decide.

Anger needs somewhere to go, and writing gives it that without handing it to anybody. The hour is what separates the feeling from the sending, because the version of you that typed it and the version that reads it back later want different things. Most of those messages do not survive the second reading.

Keep the draft somewhere it cannot send by accident, then come back and read it as though it had just arrived from them. Notice what you would feel. Send the part that is still true and useful, and delete the part that was only there to land a hit.