Sub folders for saved messages

Hi, I was wondering if it is possible to get sub-folders created in the savebox. Since I'm running the MPCC next year it would be helpful if I could add a sub folder for all the MPCC stuff to keep it separate from all the e-mails with members' addresses, which is what I mostly have in there now. I'm sure many others would find sub-folders useful for sorting their e-mails as well.

If this isn't too difficult could this be done quick