This is great info! I bubble-wrap each egg too but instead of using egg cartons, I put them in a DHL bubble pack bag. I add packing peanuts and pine shavings between each egg. I layer the bottom of the box with more packing peanuts and shavings, lay the bag in, then more peanuts and shavings around and on top.
The other post was correct in not writing "fragile/eggs" on them because those boxes tend to get mis-handled more than "fragile/glass".
Our mailman also told us that when the mail comes in, the boxes are tossed into bins by area, regardless of whether it says fragile or not. They "try" to toss the bigger boxes in first but there's no guarantee. He suggested sending by certified priority mail because they are more careful with certified and WALK it to the bin. Again, no guarantee that a heavier package won't be tossed on top of it, but at least the box itself isn't tossed.
Hope this helps -
Cindy