I searched the forum for "mailbox keys" and found this thread.

This post is somewhat off the original subject of the thread,
but here goes. We sold our home in TV and during closing
we were told we had to pay (again!) for the mailbox keys,
even though we returned them. Equally puzzling is that we
had to pay for our gate access cards (again!) even though
we returned them as well. What is going on here, are TV authorities
double-dipping by charging for returned, undamaged keys and
access cards? Or has anyone else encountered this? We did
not use the official TV realtors. Still scratching our heads
over it. I was expecting a refund of the deposits we originally
paid. Now not only does that look unlikely, but we had to pay
to return the items which we previously paid deposits on!

Hopefully someone can explain how it works....