I set up this intelligent mail box with 2 sensors and one transmitter.
Magnetic door switch $2.00
Mail sensor ( i invented it :) , works 1000 times better than distance sensor, or other you may use).
RF transmitter Kit for $4.90, you only need the transmitter for this.
Arduino/Compatible from $23
Comparing the size of RF transmitter module with an old Nokia
To connect any switch, im using these “2pin plugable terminal module” sold by Seeed Depot, which is very useful.
Here is the mail sensor, basically its a simple switch, with two separated metal parts, they are very flexible in order to make contact when a new mail touches.
Mail box, red would be better ;)
I pasted one part of magnetic door sensor to the box, and the magnet part on lock, so when we turn the key to open door, this magnet will go up.
Adding the box with arduino, and connected sensors.
Here we can see mail sensor attached to mail box and a external power supply.
Creating a new policy one server, this policy has only one filter, when new_mail value equals 1 then the action is triggered, which in this case was a SMS notification.
New mail arrived!, check out the video