In Episode 1, Sam sends a raven to Jon regarding the dragonglass at Dragonstone. In Episode 2, Tyrion (at Dany’s request) sends a raven to bring him to Dragonstone. Later in the episode, Jon receives Sam’s raven about the dragonglass. In Episode 4, ravens (presumably) were sent to Dany informing her about what happened at Casterly Rock and Highgarden. In Episode 5, Bran sends ravens to the Citadel. In Episode 6, Sansa receives a raven from Cersei, inviting her to King’s Landing.