I think they're great but they seem to need tweaking. My thoughts:
~needs a "reply" button (others mentioned this but I'm collecting various ideas in one place)
~needs a way for sender to choose how many of an item to send rather than just a whole stack
~would be nice to be able to attach more than one item as well rather than spending 20 currants multiple times if you are sending several items to one person
~I don't get why the mailboxes can't perform both send and receive functions...maybe it's a tech thing (I'm clueless tech-wise). Just very weird to me that I can't do either/or at one spot.
Anyone else got mailbox ideas? Those are mine:)