ATTACH THE BACK AND TOP .
Fasten all the pieces on the mailbox with exterior wood glue and 2" deck screws. Although cedar is a fine outdoor wood, it can be quite brittle. To prevent splitting, drill 1/8" pilot holes and counterbore the holes 1/4" deep, using a counterbore bit. Space the screws evenly when driving them.
1. Cut the back (B) and top (C) to length. Fasten the top between the 2 1/2"-wide faces on the two sides with glue and 2" deck screws. Position the top so that the rear face is flush with the rear side edges, and the top face is flush with the top side edges.
2. Use glue and deck screws to fasten the back between the sides, flush with the 10 1/4"-long edges (photo B), and butted against the top.