This was the answer I got two days ago: "Beginning tomorrow, the Grad School will send out letters to all applicants with the committee's decisions". I was also quite surprised, considering that they used to send emails in the last years.
Hi everyone, first time poster here... I emailed the department at Princeton asking whether all successful applicants had already been notified and they answered that the Grad School began sending out letters to all applicants yesterday. It seems that this year rejections and probably waitlists are coming by mail...