[Dovecot] how to configure quota in horde

[juan carlos]

Hello Everyone:
I am configuring horde/imp with quotas, but i have some problems.
I have horde 3.0.4/imp 4.0.2/mysql 4.0.24/postfix/dovecot/apache2 on debian 
sarge, I put the quota of 10 MB. The users are virtual users, they are not 
users of system (linux). What can i do to show user's quota if the users are 
stored in my database (mysql)?

This is my table mailbox:
 
select username, home, maildir, quota, domain  from mailbox;
 
+------------------+--------------+-------------------+----------+------------+
| username         | home         | maildir           | quota    | domain     |
+------------------+--------------+-------------------+----------+------------+
| test at domain.com  | /home/vmail/ | domain.com/test/  | 10240000 | domain.com |
| test2 at domain.com | /home/vmail/ | domain.com/test2/ | 10240000 | domain.com |
| test3 at domain.com | /home/vmail/ | domain.com/test3/ | 10240000 | domain.com |
+------------------+--------------+-------------------+----------+------------+

Thanks for your help.