E17000 — MailboxAddressTaken

This address is already bound to a mailbox on this domain. Choose a different local part.

The request conflicts with the current state of the resource, including idempotency conflicts (E01004, E01005). Fetch the resource's current state and reconcile before retrying. For idempotency conflicts, reuse the original request body with the original key, or mint a new key for a genuinely new request.