I dont want to mess around too much, but would it be possible to delete roundcube? If that is possible i can upload my own index.html which redirects to the Rainloop installation on my NAS
(like I did with http://Hoeky.nl/webmail/
This will not change the way nginx serves index files (index.php files will not be served unless done by name: http://example.com/index.php works, but http://example.com/ will show a 403 error.)