Ah, this is something I always wanted to have for my MUA of choice, but never dared to ask: per folder sorting rules. It's as easy as:

  > Yes, press M S R O and configure this, or if you have enabled
  > [X] Enable Take Rules
  > then simply press "T" in the folder you want to use and then from the menu
  > in the bottom, select "O".

...and how intuitive ;-)