Use email when it is more convenient than other forms of communication. It often is, but a business where everyone sits and sucks at their email becomes more introverted than extroverted. Also limit circulars to anyone of the type: “I can't find my ballpoint pen, have you seen it?” or “Try to see a disgusting porn picture I happened to find on the net”. And remember the only difference between an email and a postcard: You may be able to intercept the postcard by knocking down the postman, but the email is irrevocable. That's especially true if you're a little annoyed and going to hit “reply” instead of “forward”. See also “Social Media”.