The concrete and the four 4X4's got the test this winter by being hit with high speed snow blasts by the snow plow several times. I just checked and they are still solid. Had the mail box damaged many times when we would get a "stand in" snow plow driver (usually young and first timer) that didn't get the phone calls yet from neighbors that lost their mail boxes too. Even the regular driver(s) sometimes couldn't avoid doing some slight damage to our or other's mailboxes when trying to keep up with heavy "lake effect" deep snows. Even had what we think were bore kids take out mailboxes with stolen large trash cans thrown from the bed of a pickup "just for kicks". Put up the 4X4's in hopes to at least minimize the snow plow damage and so far it helped. Had an older neighbor and his wife walking their dogs and overheard the wife question why the four posts? Husband stopped and then said "Hmmmm that's a good idea, remember how we've had to replace the mailbox a couple of times from the snow plow, I guess that's what they are for?"

The snowplow gets going at a pretty good clip out here and being a large "country" mailbox takes a pretty good hit........well before it did, now not so much.