Apple is bringing Hide My Email and Sign in with Apple under one domain
Apple will unify the email domains used by Sign in with Apple and iCloud+ Hide My Email under a shared domain, private.icloud.com, later this summer.

Hide My Email is a service included with iCloud+, Apple’s subscription service. It allows users to generate one-time-use or reusable email addresses that forward messages to their personal inbox without revealing their actual email address.
New email addresses generated by both services will use the new domain. Sign in with Apple currently issues addresses on privaterelay.appleid.com, while Hide My Email uses icloud.com addresses.
“Existing addresses on the legacy domains will continue to work and forward mail to users without interruption,” Apple said.
The company is advising developers that use Sign in with Apple to update account systems, email validation logic, and allowlists to accept addresses from private.icloud.com. Support for the existing privaterelay.appleid.com and icloud.com domains should remain in place.
Apple also said email service providers should update domain-based filtering, suppression lists, and routing rules that reference Apple relay domains to include private.icloud.com.
Several Apple users on Reddit criticized the change, expressing concern that websites could block registrations using Hide My Email addresses issued on the new domain.