The Lodi News-Sentinel got inside the USPS and photographed these Netflix envelopes going through the sorter. The accompanying article also says that Netflix returns can go through two stages: first to a "mail center" and then to a "hub."
As the movies are viewed in Lodi, they are sent back in the same envelope for free to a mail center in West Sacramento. From there, they are shipped quickly to a hub, or a warehouse where millions of titles are kept. For Netflix, the closest hub to Lodi is in Sunnyvale, Swasey said.
That means the PO Box addresses we've collected could represent mail centers and not actual distribution centers.