Ordinary mail has no insurance factor, and only depends on the conscience of postal staff. If you are not responsible, you may lose it, or you may put it in the counter of a post office and lose it if you can't find it forever. If you find it by luck, you may receive an expired letter that arrived several years ago! People nowadays have no sense of responsibility. Two years ago, a reporter made an unannounced visit and found that the loss rate of ordinary mail in China Post reached 1/3!