Strike while you’re calm, not while you’re hot. Anger aims badly.

Anger gives you energy and takes away accuracy. It makes you fast, certain and slightly blind, so you hit whatever is nearest instead of what actually needs addressing, and afterwards you are apologizing for the delivery rather than being heard about the point. Calm is not the absence of the complaint. It is the complaint with its aim corrected.

Give yourself a rule for the next flare up: nothing sent, nothing said, for one hour. Write the angry version somewhere nobody sees it, then keep only the part that is true. Deliver that part when your voice is level.