Laurens,

This is already available in Xeams (v6 - b5948) and has been for a few versions down.

You just need to perform the following;

1. Click "Detail view" to get the view you want.
2. On the far left at the end of the frame (within the actual email detail frame) you will see a checkbox which you can tick or not.  
3. Tick the relevant boxes for the emails you wish to select and click "Mark as Good" or "Mark as Junk" at the top.

Hope that helps.

James.