I've only just upgraded my Kubuntu to 11.10. I had heard there were issues with the new Kmail2 that uses a different database. Details at
https://wiki.kubuntu.org/OneiricOcelot/Final/Kubuntu/Kmail2
This also says that the conversion tool that appears when you first run kmail does not work and to use the command line version. I've done that, but still get the conversion dialog. I see there is a ~/.kde/share/config/kmail-migratorrc file that says it completed.
So how do I get it to accept that the data has already migrated? Or has it really?
To be honest I'm thinking of moving away from kmail as I have had a few issues with it being slow and not well supported. I may move to Thunderbird, but I need to make sure I can transfer all my mail folders.