We have this.  It is called DIMP: http://www.horde.org/dimp/

I'd love to see an option to display your email in a three windowed 
view consisting of the existing menu on the left, but on the right 
have the email listing on the top half and have a window below it 
where the email opens.  It makes it quicker to jump around your 
messages without having to jump back and forth in pages or having to 
have multiple browser windows open.  I could see this as an option 
that could be set in the prefs if you would want to view your mail in 
this way.  I'm attaching a screenshot demonstrating what I'm talking 
about.



Thanks

Greg