Mildew grows on surfaces that are consistently damp or in warm, humid climates. The mailbox post in your yard is exposed to inclement weather and, as it gets dirty, becomes a prime location for mildew to grow. It's important to remove the mildew spores early so they don't spread to the inside of your mailbox. While regular cleaning and maintenance prevents mildew development you can remove the stains and accompanying odor with supplies found around the home.
Brush mildew spores off the mailbox post using a utility broom. Start at the top of the post and brush downward to remove the mildew.
Wear rubber gloves and fill a bucket with 1 gallon warm water. Mix in four capfuls of disinfectant cleaner to make a mildew-killing solution.
Dip a scrub brush in the disinfectant solution and scrub your mailbox post. Rinse the scrub brush frequently, with plain water from the hose, then continue to wash off the post.
Rinse the mailbox post off with your garden hose. Wash away the disinfectant cleaner along with mildew stains. Let the post air dry completely.