Alice Cullen is smart enough to send a letter instead of coming in person. Though, Aro would have enjoyed another chance to read her mind; he so enjoyed her visions of the future.
However, as it stands, the Volturi kings receive a letter.
This message looks rather unremarkable at first glance as it's written on plain printer paper and sealed in a cheap envelope. Truly nothing that stands out. Despite it's lack of fanciful adornments, Aro opens the letter eagerly.
Alice Cullen probably should have come in person.