When viewing in "Threaded Mode" the sorting should sort
on the thread as a whole, not the first message. For
example, if I have a new email in an old thread, I will
have to go through page's of mail (or turn of paginate)
to find that email, as it's thread position is at the
position of the first email in the thread.
Sort by date, should sort on the date of the last
message in the thread, or something similar so that it
appears at the top of the page.