I then sent back and inquired about international, since that is what I do the most of and got this response:

Thank you for the additional inquiry. Actually, the Breezeway boarding
applies as well when a passenger is traveling from the United States to
an international destination.

I spoke with a colleague who works at the Atlanta airport today.
Apparently there has been a change to the Breezeway procedure. Zone 1
is maintained now as first class, BusinessElite boarding only, and the
Breezeway boarding begins after Zone 1. This procedure change was
implemented to prevent a backlog of boarding during Zone 1. I hope this
is helpful.

Again, thank you for writing. We appreciate your selection of Delta and
will always welcome the opportunity to be of service.

Sincerely,

Woodie Stapler
Manager
Customer Care