Ok, You have your fantastic mail server with roundcube as web client.
All work great but hey, wait a moment… how can i set a filter in roundcube?
Filtering emails in webclient (gmail, outlook etc) its a normal thing but in your mail server it’s not automatic, and you have to do a bit of work for have it in your roundcube.
This is a quick tutorial on how to configure all on Ubuntu 12.04 with postfix+dovecot+roundcube (I assume that you already installed them).
Let’s start: