Manually create Apple hidden e-Mail addresses @privaterelay.appleid.com

To use your privaterelay.appleid.com as disposable adresses is not possible at the moment, because it accepts only the developer id who created it as a sender.

It's important to understand that the email address given to the developer (you), in this case: [email protected]

may only be used from the email domains (with SPF records) or full email addresses registered in the Developer Portal. It is not currently possible for you as a developer to hand that email address to a third-party and expect to be able to route through the privaterelay.appleid.com MTAs. Unfortunately, it's also not possible to register any third-party domain such as mandrillapp.com as one of your email source domains.

At this time, mail API services that send email from their own MTAs on behalf of their developer customers do not work through privaterelay.appleid.com. The only available workaround currently is to setup your own MTA and emit mail from one of your registered domains.

We are aware of this issue and are working on a solution that would allow developers to use these mail API services.

Stay tuned...

Reference https://forums.developer.apple.com/thread/121256