Now my brain is clean with the issue. I have to study Cyrus.
It seems that Dovecote has no support for mail-quota neither Maildir[1]
thanks for replaying folks, you have been helped me a lot.
[1]: http://dovecot.org/pipermail/dovecot/2003-September/002364.html
http://wiki.dovecot.org/moin.cgi/DovecotFeatures