Should anyone be interested, here is a video of my mail arrival notification. Note that my mailbox is around 150 feet away from my house. https://www.youtube.com/watch?v=YRKtPEtqW5w
Originally I tried to use the external sensor on the GoControl contact sensor, but operation was not reliable at all. In the end I hacked the sensor, removing the internal reed switch cutting two circuit traces, and wiring jumpers from the old reed switch pads to the external sensor contact pads. This now allows me to use the internal sensor circuit with the external screw terminals. (Note that this hack does not effect the Battery or Tamper Status.) I then used a magnetic reed sensor that I bough off eBay for around $6 with shipping and wired that up to my mailbox (I did have to extend the wires though from the new reed switch.)
Now when mail arrives I receive a text notification (‘Notify Me When’ smart app,) and some lights change color, in my case Green, (‘Smart lights’ smart app.)
Now I get reliable notifications every time the mail comes, and I know I will only be checking the mail box once as our mail person comes at various times of the day. The only downside is I use a Zigbee RGBW bulbs that sometimes do not turn on even though the command is sent to them, so I ordered a Z-Wave RGBW bulbs to hopefully fix this.