The letter is written on parchment paper and delivered to the recipient by owl, except in the case of Muggle-borns, where the acceptance letter is delivered in person by a member of the Hogwarts faculty, a special messenger, who explains everything to the student and parents. Harry Potter's initial acceptance letter was delivered by regular Muggle post, as Vernon and Petunia Dursley were aware of the existence of the wizarding world and Hogwarts. Hogwarts is able to magically tell whether or not a child has read his or her Hogwarts letter, as evidenced by the bombardment of 4 Privet Drive with letters, despite at least one of them having been opened and read by Vernon and Petunia Dursley.