[Dovecot] Dovecot chrooting

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hello all i am new to dovecot and i have a small problem. I use qmail as a pop3 server and dovecot as imap. my rc script is as follows:
-----snip-----
#!/bin/sh
exec env - PATH="/var/qmail/bin:$PATH" \
qmail-start '|preline procmail' splogger qmai
-----end-----
thus i deliver mails through procmail so all mails are located to /var/spool/mail.
The problem exists when i tested chrooting and found it a very good idea to jail all my users.. *but* 
still qmail delivers mails to the real /var/spool/mail and not to the /home/chrootusers/var/spool/mail so that dovecot can pick them up. Is there any special configuration in dovecot.conf in order to chroot the /var/spool/mail to /home/chrootusers ?
some of my conf:

login_chroot = yes
valid_chroot_dirs = /home/chrootusers
mail_chroot = /var/spool/mail
default_mail_env = mbox:~/mail/:INBOX=/var/mail/%u

PS: tell me if you need more of the dovecot.conf
PS2: sorry for my english its not my native