The Polar Bear Post is how all your letters to Father Christmas get delivered to his workshop in the North Pole.
The post gets dropped off by a boat on the icy shore of the Arctic, where it's picked up by the bears who then amble across the snow with it to make sure your notes get to Santa before Christmas. Only they know the exact location of Father Christmas's house. Didn't you know that? I suppose they did rather skirt around it on Frozen Planet so you can be forgiven...*