Locate the area for the mailbox mounting. Hold the mailbox against the HardiPlank surface using your hands.
Place a level tool on top of the mailbox while continuing to hold its position against the wall. Adjust the mailbox's position until the level tool indicates a perfectly level position.
Make a mark with a pencil within each screw opening on the back of the mailbox to indicate the correct screw positions.
Remove the mailbox from the wall. The marks should be clearly visible after removal.
Create a drilled hole for each mark by using a drill outfitted with a masonry bit. The bit should be 1/4 inch in diameter.
Remove the debris within the holes with canned air or an air compressor. Press a plastic anchor into each hole.
Place the mailbox over the drilled holes. Screw in the screws with a screwdriver. Tighten the screws until the mailbox remains flush with the HardiPlank surface.