You can now train your Runbox spam filter using IMAP. Simply use your email program/app to move messages to your Spam folder to report them as spam, and move them from Spam to any other folder to report them as not spam.
IMAP training works for both the Dspam and the Cloudmark filters, the latter of which is in an open beta test. To join the beta test, just go to Manager > Filter and turn it on.
This is a great feature as I generally do not use Webmail, and therefore need a method for training the spam checker.