message list theme migration 4.1x -> 5.x

Hi,

I spent quite some time to get my message list display just right. I've just 
installed KaOS in a VM to get a bit of first-hand experience with KF5 versions I 
never tried yet (including KMail c.s.) and noticed that this theme wasn't 
imported from my KDE4 ~/.kde directory (which I copied to the VM before logging 
in to it). Sadly it seems that even an explicit export from KMial 4.1x and 
import into 5.3.3 doesn't have the intended effect.

Please tell me that somebody cared about migrating this setting too (I'm really 
not looking forward to fighting that theme editor again)?

Thanks,
René