If someone sends you an incendiary or insulting email, do not respond immediately.  Do not dwell on it.  Do not read it over and over, which will just make you angrier.  If you can, let it sit for a few hours or even overnight.  If the one who sent it is sitting on top of his/her computer waiting for a response, this will drain some of the steam out of that person like a bag of microwave vegetables.  When you do respond, respond in a calm and professional manner.  Avoid arguments over email and especially "Reply to all" arguments.  This week's etiquette tip is brought to you by Culture and Manners Institute.