Good email is often relative to the context of either the sender or the recipient.
The vocabulary and usage may vary from one setting to another. A message to a longtime friend from childhood regarding an upcoming class reunion. A message to a company whose product you are returning. These messages should be distinct not only as to their content but also as to the vocabulary used and the tone of voice. Exchange these three messages with your pen pal and then respond with your evaluation of each message and offer suggestions for improvement.