Kmail

Transfer
mail and settings to another computer (or another user account on the
same machine) 
 Solution: The messages are typically in ~/.kde/share/apps/kmail/. 
 For very old installations of KMail, the messages can also be in
~/Mail. 
 Note that KMail uses hidden sub-directories inside that directory, so
you need to make sure to copy hidden directories as well. 
 For settings you will need to copy the following files: 
 ~/.kde/share/config/kmailrc,
~/.kde/share/config/mailtransports, (since KDE 4.0)
~/.kde/share/config/emaildefaults and
~/.kde/share/config/emailidentities . 
 Your address book is usually stored in ~/.kde/share/apps/kabc/. 
 Calendar data is in ~/.kde/share/apps/korganizer 
 Be aware that some distributions use ~/.kde4 instead of ~/.kde/ for
their KDE configuration data. 
 Look at the output of the command kde4-config --localprefix if in
doubt. 
 From version 4.4 you may have some Akonadi-controlled entries that
also need to be kept. Add to the above list - 
 Everything under ~/.local/share/
Everything under ~/.config/akonadi/.
~/.kde/share/config/nepomukserverrc
Everything under ~/.kde/share/apps/nepomuk/ (KAddressBook stores contact groups in Nepomuk.) 
 If you plan to use an USB stick as transport medium for your data, be
sure to format to a linux FileSystem.