Hi I am currently developping the "Sign in with apple" feature.
We set up everything according to the documentation : https://developer.apple.com/help/account/configure-app-capabilities/configure-private-email-relay-service
When trying to send an email from one of the registered communication emails (that is SPF and DKIM Authentication compliant) the emails are still ending up in the spam box. If it can help the received email address (that is hidden) is a gmail. I can not catch what is missing/wrong on our side.