OotP, after the Dementor attack, when the Dursleys are preparing to throw Harry out.
Somewhere upthread someone mentioned that might have been the letter that came with Harry, but I’m not so sure.
I can't think of any particular reason why Dumbledor would have needed to correspond with them after that.
I don’t think Snape’s memory answered that question.
No particular reason Snape would ever even know of the letter.
Naomi Watts, Joseph Fiennes (brother of Ralph Fiennes, who plays Voldemort), and Stuart Townsend will join the Half-Blood Prince cast when filmimg starts in September. Naomi Watts will play the mother of Draco, Narcissa Malfoy. It is still unknown what roles the other two actors will play.
I pictured Narcissa Malfoy to be really tall, at least 5'10" and more snooty looking then Naomi Watts.
Anyone have any guesses on who the other two will be portraying? If a Mundungus is ever cast I vote for Bob Hoskins. He's looks exactly like what I picture Dung to look like.