So the book I received in the mail today was enclosed in a plastic bag with this message printed on it: "WE CARE. We sincerely regret the damage to your mail during handling by the Postal Service." 

And it goes on from there. But what is odd about the damage is that they got my book wet! Somehow my book fell into a puddle or something while in transit. And it was definately damaged after it was mailed because these stain is clearly visible on the wrapper.  Unfortunately the sender didn't use a plastic inner wrapper.

I know PBS recommends books have an inner wrapper of plastic to protect from moisture while sitting in your mail box. But since I have a box at the post office, I never thought water damage would be a problem.

Just goes to show: always wrap your books in the plastic inner wrapper before mailing even if you are mailing to a PO Box address!

It's also possible that the book could have been in a container with a package that had a liquid leak. Bummer about your book!