I've installed roundcube for a client on one of our cloud servers. Though it works fine, mail transacts, roundcube seems to be missing the default folders. The only folders that show are inbox and sent, no junk folders. What's happening is that all legit mail that goes into spam is overlooked since there is no junk folder to access it.
Before making any changes in roundcube/config/main.inc.php file make sure that you have taken backup for roundcube/config/main.inc.php file, so that if any thing goes wrong you can restore original file from backup copy