We’re currently tweaking the Runbox spam filter configuration to catch more spam.
Specifically, we’ve fixed an error that caused messages with a valid DKIM (DomainKeys Identified Mail) header to pass straight through the spam filter. Since some spam unfortunately includes such a header we now scan messages regardless of their DKIM status.
We have also tweaked the spam score given to messages sent from dynamic IP addresses, which can also be an indication of spam (although most such messages are of course innocent).
We would be interested in your feedback regarding the spam situation in your own account and whether you see any improvements.