I consider the usage of Roundcube for the UI a downside. I've tried Roundcube myself and was not really satisfied. It is difficult for to describe what exactly

I consider the usage of Roundcube for the UI a downside. I've tried Roundcube myself and was not really satisfied. It is difficult for to describe what exactly is wrong with the UI but somehow the usability is not really good. Outlook (web), GMail, or Yahoo Mail all feel better to me. What I'd really miss would the integration of an external adress book (Google), because I wouldn't want to duplicate all my addresses.