When my son applied ED 2 years ago, it was released on the portal at midnight on the day that the admissions office indicated. (If I remember correctly, it was Dec 15???) There was no email. We all went to bed and got up at 5 am to check the staus and there was an official letter in the portal. The FAT letter came about a week later.
Just got an email from CMU. They said the decisions will be revealed online on Sunday, December 11th.