[CentOS] Horde mailboxes with Virtualmin and CentOS 6

I'm sorry if it is off-topic, maybe not.

I have CentOS 6, webmin/virtualmin panel and I just install Horde 3/imp 4.

In my virtualmin panel I have many email configured, but when I acces  
Horde and I try to login with email/password or user/password, Horde  
tell me login or password not good.

What I have to do to synchronize Horde and virtualmin mailbox?

Thanks you


Ernesto