What are the differences between "My Stamps" and "Stamp Collection"?

My Stamps comprise the stamps you unlock by achieving hidden tasks, downloading from the Stamp Store, or receiving as gifts from your friends. These stamps are stored in your album of My Stamps, and you can use them in your own letters for an unlimited number of times. 

Stamp Collection includes all the stamps in your My Stamp album, as well as the stamps you have received from your friends' letters. This album functions like a stamp collecting album for viewing purposes only. It reflects the concept of real-life stamp collecting, where you cannot reuse a stamp from a received letter, but you can preserve it by placing it in your stamp album for collection and viewing.