My comment was that an architecture with everyone using a
central server
is not an "edge" architecture. It is an infrastructure architecture.
That is not the proposal, the proposal is that all users from
a specific domain channel their email through a predefined set
of gateways.
Sure this is not compatible with the 1970s era 'end-to-end'
ideology. The fact is though that almost no corporate, government
or large academic networks have been structured in that fashion
since the mid 90's. The only major network I am aware of that still
adheres to purist 'end-to-end' is the MIT network.
If you look at the vast majority of real networks (90%+) you
will see that they are infrastructure designs. The border between
the internal network and the network of networks (aka Internet)
is defined and controlled by means of a collection of firewalled
machines.
'Changing' to an infrastructure architecture is not an issue,
that took place ten years ago.