If your mailbox has seen better days and has a definite lean, it might be time to repair or replace. First, it’s important to make an honest assessment of whether fixing is your best option. If the post is cracked, broken, shows signs of decay or is severely bent, replacing it might be the best option. If a little crooked or wobbly is all that’s wrong, then fixing a leaning mailbox post should not be that difficult. (unless the previous installer used concrete) Use a level to see how far off the post is, side to side and front to back, then push or pull the post to move into a straight up position and secure it with braces. Remove some of the dirt or fill around the post and replace it with some type of wedge material, sand, gravel, rocks and/or dirt. Soaking with water at this point could also be an option, then add additional dry material and tamp securely in place using a heavy tool or similar type implement. If using concrete, excavating additional material around the existing post is going to be the first step. Using a level, secure with braces after determining post is straight and mix and pour concrete according to the directions. Remove bracing after concrete has been set.