Now, they will be "blah@private.icloud.com"

I've been in the ecosystem long enough to have .iCloud.com, .me, .mobileme.com, iTunes.com, and probably one or two more addresses all assigned by various Apple services over the years before they started unifying the systems.

They all work, and independently of one another.

I wonder if all the domains will be migrated, and how namespace collisions will be handled.

Apple stated legacy aliases will work as is:

> Existing addresses on the legacy domains will continue to work and forward mail to users without interruption.