Which network protocol has the longest range?

The mailbox will be opened to put in the mail, which is presumably the event you want to capture. So most people find the sensor transmits that event just fine because the mailbox is open. I’d suggest you just try a sensor and see if it works without needing to do anything else. BTW, a log of people use a tilt sensor for just this reason. :sunglasses:

If that doesn’t work, usually the next step is just to drill a small hole in the mailbox and put something over the hole which is waterproof but doesn’t block signal. Usually just a thin sheet of plastic will do.

Have you had a chance to look at the following thread yet? It might give you some more ideas.