Installing a mailslot on the door - which piece goes inside?

Ok, I ordered this tiny mail slot for the front door, and it's got two
parts - a "rim" designed to go around a hole/slot in the door, and a
piece that shaped exactly the same, but solid (ie, it covers a slot in
the door). It's obviously supposed to simulate a little door that
covers a mail slot.

My grandparents had one of these mail slots, and I even remember
playing with the little door that covers the slot when I was a small
child. However, I can't remember if the little door (solid piece)
goes on the inside or the outside, and if the decorative rim goes
inside or out.

I *think* the solid one goes on the exterior door (the mail carrier
would lift the door, and slide the mail inside), and the decorative
rim goes on the inside. Does that sound right?

Cathy Weeks