I primarily build mailbox housings out of vinyl material and this has become the preferred material over cedar mailboxes for nearly all home owners. In addition to having the same look as a cedar housing, the vinyl housing has many advantages:
will not rot, crack, splinter, split, swell
impervious to moisture, insects, and termites
naturally resistant to mold and mildew
paints great
all joints are cemented
never any knots