If you ever read your email in Hotmail, you know how much of the screen is taken up by all the Hotmail information and advertising. There isn't a great deal of space left over for your email.
Keep that in mind. Be aware of how much of your message will appear on the first screen. And make that information count. You'll need people to start scrolling down to read the rest of your message. And they won't bother to scroll down if the first few lines of your message are not sufficiently compelling and relevant.
Source: FreelanceWriting Tips