how to move email to new system

[Default User]

Hello! 

I am doing a new install of Ubuntu 7.04.  I would like to transfer the
email from Evolution on a Debian system, to the Ubuntu system.  What is
the best way to do that?  

Extra credit question: why do email programs not store email messages as
normal text files?  Or would that be too simple, be too easy to
maintain, and make too much sense?  

Thanks for any input.