Depends on the setup but ideal conditions you can get up to 300ft or more. By design it says 500+ft but in practice expect between 50to 300ft depending on your setup, ie. mailbox construction (plastic, metal, brick), trees, landscaping objects etc. In our setup we have it at about 75ft from the building in the mailbox (open to the elements) and it’s been good for about 2 years now.
Do note that it always helps to keep a mains powered Z-Wave Plus device (repeater) connected to an outlet (GFCI) on the outside of the house, in the closest spot/direction of the mailbox and that helps a lots. Without the repeater device the range may drop significantly depending on how many walls/obstructions the signal needs to get through.