Use a level to draw a horizontal line on the house at the elevation for the top of the mailbox.

Pre-drill the clearance holes in the mailbox for the bolts.

Transfer the location of the clearance holes in the mailbox to the house wall at the line drawn earlier. Hold the mailbox along the level line and pass a small masonry bit through the holes and into the house wall to mark their location on the stucco.

Enlarge the holes with a bigger masonry bit. Tap in plastic anchors to ensure a tight fit and hold the screws in the masonry.

Hold the mailbox in position and install pan-head screws through the redwood and into the anchors.