postman question (possible spoiler)

yes, I'm commenting on a 5 year old made for TV movie.
I want to know, how did the postman know that Jake was Santa? (when Celia gave him the letter at the poetry reading he said something about christmas miracles while looking at jake's coat, which he then put the letter in to).
Was it just intuition? Or did everyone connected to the post office know who the Dear Santa guy was?