Our website supports Apple login, but after logging in, the server obtains the private mailbox of Apple users, but we found that sending emails to this private mailbox failed. The following is the response result I sent to the privacy mailbox using Google mailbox
Hi @lzr,
All communications to the Private Email Relay service need to be authorized and authenticated. Please configure your email domains and sources and validate your SPF and/or DKIM authentication by following the documentation below:
Configuring your environment for Sign in with Apple https://developer.apple.com/documentation/sign_in_with_apple/configuring_your_environment_for_sign_in_with_apple#3743946
This misconfiguration is the underlying of cause of the 550 5.1.1 unauthorized sender error. However, in the future, if you receive an error such as 550 5.1.1 unknown user, this likely means the user has disabled email forwarding for your client. For more information, see Manage your apps with Sign in with Apple.
Cheers,
Paris X Pinkney | WWDR | DTS Engineer
