Abstract: A door sill and a sealing mechanism engage one another analogously to a rack and pinion in order to automatically create a weather-resistant closure at the gap between an inswinging exterior door bottom and the floor below. The sealing mechanism, which fastens to the door bottom, contains a door-wide rotating shaft with an arm extension tipped with a flexible seal. On the underside of the shaft extension is a short “pinion” component with elongated teeth that engage in corresponding recesses in the sill, raising and lowering the seal in the process. The pinion is positioned on the far lock side of the door, so that the teeth engage and the seal begins to drop only when the door is nearly closed. As the door opens and the seal rises, a magnet further retracts the shaft extension and retains it until the door is again closed.