Do you think it’s a desktop gadget for Gmail? You’re wrong. POSTCN01 is used in real world, but not in Matrix.
POSTCN01 has two parts, a sensor with an aerial put in mailbox and a display located inside home. You can monitor the number of letters or packages in the mailbox.
The little gadget isn’t very practical, but it’s still a novel idea. POSTCN01 comes from Japan. If you need be, you could get it for about $55 USD from Amazon Japan.