Version:            (using KDE 4.1.0)
Installed from:    Unspecified Linux
OS:                Linux

I had difficulty in copying over my Receiving accounts for kmail from KDE 3.5.9 to KDE 4.1  
The receiving accounts were not showing up in KDE 4.1 kmail settings, both POP and IMAP.

Here is how I had been copying over the configuration:

cd ~ # work in home directory
rm -rf .kde4/share/apps/kmail
cp -ra .kde/share/apps/kmail/ .kde4/share/apps/

cp -a .kde/share/config/kmail* .kde/share/config/mailtransports .kde4/share/config/

cp -a .kde/share/config/emaildefaults .kde/share/config/emailidentities .kde4/share/config/

Despite .kde/share/config/kmailrc being copied over, the receiving accounts were ignored.

This warning appeared at runtime for the number of accounts I had:
"Attempt to instantiate a non-existing account type!"

I created a new Receiving account and compared the kmailrc settings with the old kmailrc.  I found they looked similar except that the Type lines differed:
Type=pop 
Type=Pop  <-- new
and
Type=imap
Type=Imap <-- new

Capitalizing "pop" to "Pop", and "imap" to "Imap" caused all the accounts to be recognized when starting KDE 4.1 kmail again.

I don't know if this procedure needs to go into an update script or if KDE code needs to be changed to recognize the old kmailrc format.  But this is how I manually solved the problem.