You should study what makes you defensive. The topic you avoid, the joke that irritates you, the question that feels insulting, the feedback you instantly reject. Defensiveness is usually the guard dog sitting in front of a weakness you have not trained yourself to face.
"The greatest remedy for anger is delay."
— Seneca
Sit on the message for one night.
Sleep on the email for eight hours.
The reply you would have sent at 9 pm and the reply you will send at 6 am are not written by the same man.