Stop Akonadi and related applications quit KMail/Kontact/KOrganizer, and issue this command:

akonadictl stop

Make sure no Akonadi or MySQL process is running:

ps -ux | grep mysql

ps -ux | grep akonadi

They should not show anything else but the grep process itself.

Remove old Akonadi database and config

Delete the following folders

~/.local/share/akonadi

~/.config/akonadi

Delete also the files starting with akonadi from

~/.kde4/share/config

Restart Akonadi server

akonadictl start

Done, now add back the accounts