Maggie's Letter

From Zelda Wiki.org

Maggie's Letter can be obtained after Maggie returns to Windfall Island and becomes rich. She tells Link about Moe the Moblin, and gives him this letter to be delivered Moe. After putting Maggie's Letter in the postbox on Windfall Island and returning to Maggie's House, Link finds Maggie's Father arguing with Quill, the Rito postman. Once the postman leaves, if Link goes to the Coffee Shop he will find Quill there and be given Moe's Letter. Bringing this letter to Maggie will result in Link being rewarded with a Piece of Heart.