When I dropped off my letter I asked them (USPS) about this very scenario. I was told it's "optional", and at the discretion of the delivery agent, unless I "opted out" of it.
I asked how to do it (opt out), and on the little screen where I made my payment, sure enough, there was a place to "check" if you didn't find this acceptable.
I couldn't check it fast enough, but then I got to wondering about what kind of a world do we live-in where we have to opt out of something so that we get the service we're actually paying for in the first place?