Google is introduces a new way to compose Email messages in Gmail. Instead of loading a whole new “compose” page, you can now start a new email from wherever you are in a popup window. The window is not actually a new browser window, but rather an overlay on the Gmail page. The new compose looks like a Gmail chat window, though the compose version is a bit bigger.
The new compose window is rolling out as a preview today. If you would like to try it out just click the compose tab and Gmail will ask if you’d like to try the “new compose experience.” Press that link and you’ll get the new interface.
The change makes it easier to reference old emails while you’re composing a new one, since you don’t need to leave whatever page you’re viewing just to write a new message.
The overlay window also means you can search or keep an eye on incoming mail while you write your new message. Having compose in its own window also means you can write multiple messages at once and even minimize a message to finish it later.
( Via WebMonkey )