Sirtobi's change did work for me as well!
Thanks a lot!If you would like the preview to be vertical, I guess you'll have to change the template files in
/skins/default/templates/I haven't tried yet.
Update: There's a template available for the vertical colums. See this thread:
http://roundcubeforum.net/forum/index.php?topic=2217.0It contains some screendumps as well so you can see how it looks.
Regards,
Marco