Any Member or Catalyst is entitled to an @enspiral address.
They pay an additional annual fee to the foundation which is set by the board. See the current cost at the Email accounts guide
Any Contributor with an active subscription (full or subsidized) can keep their email address regardless of how / when they received it.
Catalysts can decide exceptions to the rule
This agreement was formed through the Assembly Sprint | April 2019 via this Loomio thread