I read this great book by Mark McCormack, founder of IMG and the man who became the first sports agent when he started representing Arnold Palmer in 1960. He wrote the book in the eighties, before email (and forwarding) really existed, but most of the book contains some phenomenal insights that are applicable in contemporary settings.
One insight that stands out: assume anything you write will be seen by everyone.
This eliminates the need for a BCC field and makes you accountable for anything you type to someone you now trust, but later may regret trusting. It also means that anything on your social networks or blogs can and will be used against you in the court of public opinion. It means talking shit or trying to rip people off will not work. It forces you to be better at your job, communicate better and not cheat.