Merchant Outbox fails in Linden's official Viewer for Linux.
Please refer the following link. http://wiki.secondlife.com/wiki/Release_Notes/Marketplace_Current
In Windows Viewer, it doesn't work for me.
When I change my viewer's language from System Default to English, it works.
However the direct delivery system has some troubles, so please be careful to use.
Please see the following link for more details. http://community.secondlife.com/t5/Merchants/Marketplace-and-Direct-Delivery-Update/td-p/1462915