I post my reply without read yours.
Why I am using mailscanner? That is a good question. I don't know
I follow this how to http://www.howtoforge.com/perfect-se...ot-ispconfig-3
but I have Debian 6.0.2
Without installing Squirrelmail, and a piece of this http://www.howtoforge.com/extending-...ze-ispconfig-3
for install Roundcube