It seems to me it's time email followed the file-sharing industry and moved to a distributed, peer-to-peer system. End-to-end encryption and no servers to shut down... There's a couple of research papers on the topic:

http://www.computer.org/csdl/proceedings/cse/2008/3193/00/31...

http://www.freepatentsonline.com/y2009/0144380.html