The Fine Stationary allows you to write a fancy letter and send it through Mailboxes to other players. The Fine Stationary can be colored by dragging any Dye onto it.
The text menu disappears quickly, so you should write very fast! Alternatively, you can type the note ahead of time in a text editor and copy paste it into the note in-game. Keep in mind the notes have a maximum character count of 200, including line-breaks.