1. Your address data (to, cc, and bc) is longer than your text. Use Twitter or text instead.
  2. Visible recipients (to, cc) don't know one another's email address...until you reveal them. (Unless the point of the message is introduction.)
  3. BC messages don't describe the recipients in general ("members of the committee"). Otherwise you spawn many unnecessary emails forwarding information to people who have it.
  4. You send multiple formats of an attachment (DOC, PDF, JPEG...). Use collaborative tools like Slack and Dropbox instead)
  5. You need multiple versions of an attachment (Thursday after meeting, Friday with client...). Use collaborative tools or web so that the current version is known and accessible.