Install Mail Perspectives 4.5

Mail Perspectives adds four new kinds of windows to Mail to give you four new ways to keep your Mail workspace both visually and efficiently organized.
Your email is often something you want close at hand but never in the way.

Whether you want to see the latest message or the recent message list, Mail Perspective's compact window design means your email can always be visually available, but never the focus of your attention until you need it.