I've managed to setup Roundcube, am getting my mails - can send them as well.
But reading the messages ...
Clicking on a message only produces a "forever running" "Loading ...." and an empty body. Regardless of if they are html messages or not. (Which some earlier messages/bug reports mention).
EDIT: apparently it has something to do with requisits for Carddav as I get
Fatal error: Class vobject_location_property contains 3 abstract methods and must therefore be declared abstract or implement the remaining methods (Sabre\VObject\Property::getValueType, Sabre\VObject\Property::setRawMimeDirValue, Sabre\VObject\Property::getRawMimeDirValue) in /var/lib/roundcube/plugins/libcalendaring/libvcalendar.php on line 1339
which comes from Carddav requirements. How do I uninstall the Sabre\VObject correctly?
EDIT 2: Seems you have to move libraries out of the Roundcube folder. Else the error remains even after deactivation.