Remember that August was on the other side of the world when Emma came to StoryBrooke and had his “painful reminder” that he was supposed to be watching over her and that was before Gold created the purple magic smoke.
Whoever the mystery man was in New York who received the postcard is obviously from FTL…perhaps he was unable to enter StoryBrooke until the curse was broken, or did not want to until their was magic.
Perhaps the curse only contained those that Ragina threatened at Snow and Charming’s wedding in StoryBrooke and other characters are spread throughout the world.