I received my email as well:
“We have made an adjustment to the production date for your 2021 Mustang Mach 1.
Your vehicle is now scheduled to be built the week of December 27, 2021. We will continue to keep you informed regarding your vehicle's production status.
The last email I got was in mid September, bringing me back to my original date of Nov 08.
I haven’t been getting emails lately that many of you are getting.
I had to call earlier this week to get an update (Nov 29).
But now I’m seeing posts that may indicate even later.