[zeroryouko]

It doesn't sound like Ringo is even going to be singing this herself; rather, Ringo wrote it and it's sung by one of the characters in the video. Also, by postal insurance, I think they really mean personal life insurance offered by the post office (which, in Japan, functions like a big bank in addition to delivering mail) instead of insurance against lost or damaged goods. Carnation redux may actually be pretty close to the mark.