Also check out the frequently asked questions page written in English (also available in Korean and Simplified Chinese) here!
It addresses these issues:
"I have not received an item (domestic/international) that I know was sent *Explains how to read your delivery notice (if you received one) and also where to contact if you did not receive a delivery notice
"Is it possible for Japan Post to cover damage to delivered items (domestic mail/international mail)?
"I am moving soon (inside/outside of Japan). How can I have my mail forwarded?"
"I will be away from home for a while. Is it possible for the post office to hold my mail while I am away?"
"What options are available for sending parcels and letters overseas?"
"Is there an easier way to fill out the labels for international mail (EMS, etc.)?"