Coworker went off on the boss

Have any of you been copied on an email where a coworker went ballistic on his boss for a hiring decision? He called his boss a liar and deceptive. He went on to say how his boss is causing people to be ill.

I was in shock when I read it. He included as a cc his boss’s boss. He also sent a email to the administrator. I never brought it up to my boss as I don’t want him to think I had any part of it.

our office us toxic though. I filled out my retirement papers today.