The Postman Pig is a Medium Pig found when the pause button in any level is clicked/tapped. He has updates in the level currently played. When tapped or clicked on when happy, he feels sad and a rain cloud appears above him. When tapped or clicked on when sad, he feels happy. When he is sad, the updates disappear. When he is happy, they reappear. There is a plush toy of the Postman Pig. He did not appear in the version 2.0.0 & version 2.0.1 of Angry Birds, but he returned in version 2.1.0. He slightly resembles the Mechanic Pig. unlike the other pigs postman pig doesn't appear as an enemy to the birds and is just a mailman.
The Postman Pig may be friends with the birds, as he is the only pig that has nothing to do with the eggs being stolen and doesn't appear as an enemy in a level. Either that, or he's just a neutral character.
He looks similar to the Mechanic Pig in Bad Piggies, the only difference being Mechanic Pig's hat only covers his left ear, whereas the Postman Pig's hat covers his whole head but in Angry Birds Friends he only covers his right ear on pause ads.
Postman Pig does not appear in the pause ads any more, but he still appears on the pause ad of Angry Birds Friends.
A pig that resembles the Postman Pig, with the updated Toons design as well as slightly updated hat and sack, has recently appeared in a message in regards to Clan Events streaks in Angry Birds 2.
He even helps the player by giving three spells; since the Postman Pig from the classic game gave a hint to find a Golden Egg, the willingness of this current Postman Pig in helping you instead of his own kind implies that it may be the one and the same.
Postman Pig plush
Postman Pig when he is sad. (Old Look)
Postman Pig happy (Old Look)
Postman Pig Join Newsletter
The Rovio sprite sheet for the postman pig in game
Postman Pig (in Facebook) happy
Postman Pig (in Facebook) with his newsletters missing.
Piggy reads the newsletter and postman is happy
The Postman Pig lookalike in Angry Birds 2 giving you three Pig Inflater Spells.