Yeah it's there, you have to be in the Messages section.
Speaking of the PM outbox, not that I'm saying you should work needlessly at this, I've never understood why your sent messages aren't always auto stored unless you specifically delete them. Just like any email service. Instead of manually needing to check the store message in Sent messages check box.
I've also hated how the search was, with the check box, is defaulted to everything, and the sub-forum list is always hidden. Then after you expand the section, if you hadn't clicked the search all check box, it's now located at the bottom. It's only 2 extra clicks, but still annoying.
As for the arrow pointing in which direction is expanded or not, I agree it does look confusing and backwards. Overall I'd prefer to see a plus and minus.