Yes. Upon moving out, you have to transfer possession of the property back to the landlord. This is done, most basically, by returning not just a key, but any and all of your keys. If you did not return your keys, you technically haven't transferred possession. Often this is done either through the mail, at a walk-through with the landlord, or otherwise in person, though a lock box seems like a perfectly acceptable way to accomplish the same, as well.
Answered on Feb 23rd, 2012 at 12:44 PM