I've been using SmartSieve http://smartsieve.sourceforge.net to manage the sieve scripts to forward the mail marked as spam to a spam folder.
I'm hoping that once the plugin API is ready we could make (manipulate) this into a plugin for RoundCube.

On Mon, 2007-02-26 at 11:23 -0300, Luciano M. Guasco wrote:
Hi everybody... I have installed spamassasin in my mailserver. Because I 
work in an university environment, I can't discard messages marked as 
***SPAM***, but everybody that uses roundcube have a lot of mails in 
their inbox marked as spam, but they cant redirect through filters. Are 
filters supported in roundcube? If not, I would like to program them in 
php... some suggestion???

Thanks, Luchux.

Luciano M. Guasco
sysadmin cs.uns.edu.ar
Universidad Nacional del Sur
Bahía Blanca - Argentina