How to show the size of messages?

[test]

On Saturday, January 25, 2020 2:45:08 PM CET Erik Quaeghebeur wrote:
> > how can I show the size of messages in the message list?
> 
> Have a look at
> 
> 	View > Message List > Theme > Configure…
> 
> and experiment a bit. I just cloned the theme I was using, added the ‘size’
> box somewhere and applied it. Worked perfectly.

Thanks, I found the window, see screenshot.

Apparently I am supposed to drag fields from the middle part of the window to 
the lower part, and when I drag the Size field, nothing happens other than 
that the mouser pointer changes.  It doesn't matter which field I'm dragging.

The text at the bottom of the window mentions columns and "more options".  I 
don't see any columns, and I'm not seeing any "more options" either.

Is this somehow buggy or just utterly bad GUI design?