There must be a setting somewhere on this because one of my accounts comes up with the reading pane always displayed, and the other never does. I like never, because I don't want any message marked as read till I choose to read it. Trouble is, I can't find that setting anywhere!
And if the setting is actually (save the state last used) then I've got a problem there too, because in the account that shows the pane, I go in and turn it off every time I log on, and it's back next time, every time.
It's a small thing, I know, but it's a real "pane". . .