What Comes in Over the Transom

I recently used the expression “come in over the transom” to describe the random arrival of blog post submissions. I was talking to someone who had no idea what a transom was. It is a flip in section above a door to let air in without opening the door. My college dorm had transoms. And apparently my voice carried in just a certain way so that when I talked in the hallway it came over the transom.