I'm finishing my undergrad at NAU and from what I heard from the CSD staff that I know, the letters will be sent out like what is said in the email. They told us that they are so far just acceptances and didn't really hint on when rejections would be sent out. But if you do get accepted you have until April 16th to let the CSD department know.
Let me know if any of have any questions about the CSD department!