Rare Items can be obtained from friends or bought with Gold Coins. You can send a request for Rare Items to each of your friends. The request will be valid for some time, during which your friend must confirm the sending. Once your friend does that, the item will appear in your mailbox.
Please note that one friend cannot send several identical items at the same time. You can receive no more than 5 identical items and 15 points of Energy during the day. The number of requests that can be sent to friends at the same time is limited.