yo dude, if the B is just your colleague, don't even give a shit about that, just do what you're supposed to do and get along with your leader or boss. and if he continues pissing you off, just fuck him up back. you've to stand up for yourself when someone tries to tease you. It's the rule of survival here. Hope you can get it through.
be straight. don't beat around the bush and don't be naive. just send this mail to your manager and explain you have received by accident a unprofessional lettre and probably all your colleagues received it, and tell him you appreciate your job. write to the sender also and explain you don't want to leave and ask an explanation for this.
chinese manners don't work here.
anyway, speak, speak, speak. don't be deaf and dumb. try to be friend, wise, confident,open minded, the most excellent in your company, if you are not. but never to be fooled or bullied by some else.