re: How deep do I need to bury a mailbox post to get it "good enough?"

some old man fell asleep and ran right into mine, throwing it into my neighbors yard.

Snapped the cast aluminum right off at the bottom. I ended up drilling few holes in it near the bottom and fastened some angle iron to it until it was sturdy. Then dug about 18" down and wide enough for a sack of quickrete. It's held up for years but does have a slant to it.

I did the same to the lady's across the street and its held up well. Just be careful drilling