I was sitting on the couch in my living room when I heard a loud "ding dong!" chime through the house. I got up from the couch and walked to my front door. The doorbell rang again as I made my way to the front of the house. "Ding dong!" Once I was standing at the door, I raised myself up on my toes a little to be able to see out of the peephole. I saw that the person at the door was my mail delivery person. I unlocked the bolt on the door, turned the doorknob, and slowly opened the heavy wooden door and then the screen door. Once the doors were open, I cheerily greeted the mail delivery person and took the mail they handed to me. Once I had taken the mail, I then wished them a good day and I closed the door behind them as they left. 
Question: Why was the doorbell rung?
It was the mailman.