Check the weather stripping around the door for any cracks, tears, or compression.
If you find a leak at the bottom corners of your exterior door, the source could be from multiple weak points. Light leaks can also welcome in unwanted insects, as they are drawn to light and will slink in through the cracks. These leaks can affect utility bills, as your house will need to make up for the intrusion of hot or cold air. An important part of homeownership is sealing and protecting your door from air and water infiltration.