Only in Japan do people not only send cash in the mail, but also use a special envelope which indicates that, one, cash is contained inside, and, two, the amount contained. If this were ever tried in the U.S., I'm certain the system would fall apart within a week's time. Mail carriers would be cahoots with their supervisors, liberating the cash from the dark confines of the envelopes and blowing it on strippers and booze.
The genkin kakitome, or "cash registered mail" ought to be an anachronism in this age of online banking and high-tech ATMs, but no: some people still insist on using it.
The maximum amount that can be sent by genkin kakitome is ¥500,000 (roughly US$6,200). The cost, which includes insurance against loss, is ¥420 for amounts up to ¥10,000 ($124), plus ¥10 for every additional ¥5000 insured. The envelope itself must be purchased separately, at a cost of ¥20.