had message
KMail could not create folder '$HOME/Mail'
after I shortly used mandy 2006 then reverted to 2005.
(differen version of kmail)
This must have changed /home/username/.kde/share/config/kmailrc
so I edited it and replaced
folders=$HOME/Mail
by
folders=/home/username/.Mail
That solved the problem (using kontact first instead of kmail did not,
and deleting the dir .Mail did not work either)
other example (unsolved)
http://mail.kde.org/pipermail/kdepim...st/005072.html