What’s a good email?
As a reader, I want to a email like this:
1. I want to know some context of this email
2. I want to get the key point of the mail immediatly from the email
3. I want to know how you support your point and if I agree with your point
4. I want to know what and when I need to do
5. I want to know which questions I need to answer

How to write a good email?
1. Subject line is key to the email
2. Begin the email by positioning
3. Set the context and explain what you need to
4. Provide the supporting data
5. Towards the end talk about what action you want by whom and by when
6. List questions you want the reader to answer clearly and directly