April 04, 2013, 5:24 PM — Here's how you can switch back to the old compose window in Gmail.
1. Login to your Gmail account.
2. Open the compose window.
3. Click the small arrow button at the bottom right of the new compose window.
4. Click on "Temporarily switch back to old compose" option in the menu.
For more, see the original article at the link below.
Switch to Gmail’s old compose window | Ghacks