Following the pinned post "Gathering required information for troubleshooting Private Email Relay with Sign in with Apple" (thread 794191, which is locked, so I am posting here as instructed): I have filed FB24564316 with the required information. Since 28 July, every message from our app's sending domain to @privaterelay.appleid.com addresses is rejected by iCloud Mail with 554 5.7.1 [HM08], so users who signed up with Sign in with Apple and Hide My Email cannot receive their sign-in emails. Plain-text messages with no URL bounce as well, SPF/DKIM/DMARC pass on two independent sending systems, and external reputation checks are clean, so this looks like a false positive on the sending domain. The feedback contains the App ID (6761705463), Services ID, SMTP error codes and transaction IDs. iCloud postmaster case 21382576 and Developer Support case 20000139732014 did not resolve it. Happy to provide message headers. FB24564316