New domain for Sign in with Apple and iCloud+ Hide My Email

Later this summer Apple will unify the email domains used by Sign in with Apple and iCloud+ Hide My Email under a single shared domain, private.icloud.com, replacing the legacy privaterelay.appleid.com and icloud.com domains for newly issued addresses. Existing addresses will continue to work, but developers should ensure their account systems, email validation, and allowlists accept the new private.icloud.com domain alongside the existing ones.