If you go to the main pull-down menu and select Window > Tile all of the open child windows will be tiled within the main window.  They will all be available to work in but will probably need to be manipulated in size and location to your liking.

When I open new mail messages, half of the message is out of sight off the top of the screen, and the program will not aloe me to move or delete the open message. What do I do?