1°) Akonadi can't run when log as user root due to mysql protection :
[akonadiserver] Found mysql_install_db:  "/usr/bin/mysql_install_db"
[akonadiserver] Found mysqlcheck:  "/usr/bin/mysqlcheck"
[akonadiserver] Database process exited unexpectedly during initial connection!
[akonadiserver] executable: "/usr/sbin/mysqld"
[akonadiserver] arguments: ("--defaults-file=/root/.local/share/akonadi//mysql.conf", "--datadir=/root/.local/share/akonadi/db_data/", "--socket=/root/.local/share/akonadi/db_misc/mysql.socket")
[akonadiserver] stdout: ""
[akonadiserver] stderr: "110721 22:13:23 [ERROR] Fatal error: Please read "Security" section of the manual to find out how to run mysqld as root!
[akonadiserver] 110721 22:13:23 [ERROR] Aborting
[akonadiserver] 110721 22:13:23 [Note] /usr/sbin/mysqld: Shutdown complete
[akonadiserver] "
[akonadiserver] exit code: 1
[akonadiserver] process error: "Unknown error"
2°) Kmail seems to need Akonadi

So how to configure Kmail to read and delete local mail sent by other users or by system or apps ?