I never receive a notification when the mail is dropped off

I never receive a notification when the mail is dropped off but every time I retrieve it, I do. In other words, when I go to get the mail, I get the notification on my phone but when the mail carrier drops it off, I don't. Not exactly what I was hoping for. The mailbox is a good hundred feet from my house. I have the sensor mounted to the back of the back of the mailbox with the antenna lead going through the back and on the wooden pole above the box.