[Dovecot] Authenfication on 2 databases

Hello,

I have 2 databases MySQL. I would like to do that:

If the user does not existe in the first base, it goes in the second database.

my configuration

auth default { mechanisms = plain passdb sql { args = /etc/dovecot-sql-1.conf }

    passdb sql {
           args = /etc/dovecot-sql-2.conf
    }

    userdb sql {
            args = /etc/dovecot-sql-1.conf
    }

    userdb sql {
           args = /etc/dovecot-sql-2.conf
    }

}

but it don't work, my version est 1.0.alpha1

if you not understand this message, i am sorry, my english is bad