You can likely do this with RM, however this was similar code that worked for me on ST. You can set start/stop times and adjust the frequency of notification (in case you have it opened multiple times a day). I also have pics of my setup and suggested devices.
Can you please describe how you connected the internal and external contacts together?
I ended up using an Iris Zigbee contact sensor for mine. Taped the contact under the box at edge and used a small round magnet and have it on the mailbox “door”. Traveling today but can post pictures this weekend if anyone is interested.
Inside there is a small connector with 2 screw terminals. You essentially connect your reed switch to those two terminals, when the connection between them is complete, the contact sensor is closed - when you disconnect the connection, it's open. You can test it with a small wire bridging those two terminals.
I used an Aqara Vibration Sensor on the opening flap of the letter box. The sensor sends signal when the flap is moved. It works perfectly.
Those don't support zigbee repeaters, do they? It means you have to have the hub nearby?
Old thread, but I've been using a motion sensor in my mailbox for a little over a year. I have a notifier set to send a message, also triggers my blue iris to record on the cams that can see the mailbox.
My mailbox is 200ish feet from the house, but it's also a plastic mailbox.
It works fine but like many sensors, they drop out every now and then. This is a separate issue which is happening to 80% of the sensors of different brands and models that I have, including motion sensors and contact sensors.
the ones i found that have the best range and never drop out are the smartthings multi sensors.. albeit in the cold outdoors the battery only lasts about 2 months.
If you want to use Aqarq / Xiaomi sensors, this is a MUST read Xiaomi & Aqara Devices - Pairing & Keeping them connected
Just come across it. Will replace the repeaters and power outlets with the Ikea's ones over time.