Ask HN: Would you use a (physical) address verification service?

Hi,

I was wondering if anyone would use a service that validates physical mail addresses for you? Let's say your service requires a real address, or you run a promotion that is limited to once per household, we would send a postcard containing a pin number on your behalf to your user, and upon receipt they just connect to our website, input their pin number, and their address is validated. They are then returned to your website and you can proceed with 100% confidence that their address is real.

Would that be a useful service? How would you use it?

Thanks