Summarize:

When you choose "Reply," you are sending the email back to the original sender.  When you hit "Reply All," you are sending the email to all of the original recipients.  Use "Reply All" sparingly and only when it is absolutely necessary to share your response with all of the original recipients. You should use "Bcc" when the privacy of the email recipients is important.  This may be useful in group emails or large distribution lists.  You should use "Cc" when you need to include other people in the conversation and privacy is not an issue.  "Cc" is helpful when you just want to keep someone in the loop about what is going on. It is very important that you use these two functions properly.  "Bcc" should not be used to secretly pass along private information or to trap people.  For example, you should not send an email to your coworker about a mistake they made and "Bcc" your supervisor. It may be quicker to pick up the phone instead of sending countless emails back and forth.  It may be helpful to use the three email rule.  If an issue has not been resolved within three emails, you should pick up the phone and call the person. There are times when the phone is more efficient than exchanging multiple emails. Keep in mind that this rule is not set in stone.  You should use your discretion when deciding it is time to pick up the phone. If you need to discuss a different topic with the same recipient, you should start a new email. This will make it easier to keep track of conversations and will keep you from looking lazy.  For example, if you have been emailing someone about an upcoming meeting, you need to start a new conversation if you wanted to discuss the outcomes of a project that is being worked on.
Know when to use Reply and Reply All. Know the difference between Bcc and Cc. Recognize when a phone call may be better. Know when to start a new conversation.