Also, emails can be subject to discovery during a lawsuit. If you want to discuss things you don't want some lawyer looking over a year from now, you keep all discussions face to face or via phone. Email is only for things that should have a papertrail.
Personal anecdote - I can confirm this as one recently deposed in a corporate lawsuit that I'm not even a party to. Email systems are awash with information that most people would never have expected to become public. You see all kinds of stuff in emails by employees: office gossip, embarrassing comments, foul language, snark about fellow employees and competitors and the company, non-work-related comms .... all of it subject to being twisted by opposition lawyers to try to bolster their case and which can end up verbatim in front of the eyes of a jury.
