Hey guys - this was just released today, & there's a lot of information out there, not sure if anyone's missed it. So posting here! Update with whatever information you find as well.
For Customers:
The old way of delivering items via marketplace has been bugged for some time. LL has been working for awhile on a new delivery method called Direct Delivery instead of the old Magic Box method from the days of SLX. Now, if item is set to send via Direct Delivery, it will appear in a Received Items section in your inventory below the regular folder area, like this:
I think, though, that this will only show up and activate once you've ordered something for the first time with DD. You can do this now if you'd like by ordering this free Linden Bear that's burning the old magic boxes, lol.
Beauty of this is now merchants can just put a folder up on marketplace, and you won't have to unpack boxes so much anymore. Tis nice. Keep in mind, though, there's still going to be tons on marketplace that's the old method, so there will still be boxed items being sent to you the old way til that merchant updates.
For Merchants:
It's a lot of information, but worth a read. You can now send items to Marketplace via the Merchant Outbox (On Firestorm: Avatar -> Merchant Outbox, or by right clicking on the item "Copy to Merchant Outbox"). My store didn't link up at first, as the Merchant Outbox said I needed to set up a store first. But after I got the free Linden Bear, it was fixed. Maybe just needs to activate completely, I don't know. I'm looking into how I can just convert old items to the new method in the easiest way possible, but feel free to post what you find here!
Here's all the documentation so far:
Direct Delivery Launches Today
Direct Delivery FAQ
Second Life Tutorial - Converting item boxes to Direct Delivery folders