What causes '5.7.1 Email rejected due to transformation error' bounces from Apple's privaterelay.appleid.com and how to fix it?

Email marketer from Quora shares that these bounces can result from Apple having internal server issues. If you've checked your domain registration and email practices, the issue may be on Apple's side and resolve itself in time.

Email marketer from LinkedIn explains that to avoid 'transformation error' bounces, ensure you adhere to Apple's guidelines for sending to private relay addresses, including maintaining good sender reputation and avoiding spam triggers in your email content.

Email marketer from StackOverflow suggests that the 'transformation error' indicates that Apple's system is unable to convert the private relay address into a valid email address for delivery. This might be due to changes on Apple's end or issues with the recipient's Apple ID. Contact Apple support for assistance if the problem persists.

Email marketer from EmailMarketingForum says to ensure your sending domain is properly authenticated with Apple's private relay service. This involves setting up SPF, DKIM, and DMARC records correctly, as Apple is strict about domain authentication.

Marketer from Email Geeks confirms that you need to register all your sending domains to your appleid account; otherwise, the private relay IDs will not work.

Email marketer from EmailOnAcid Blog shares that to avoid 'transformation error' bounces, it's essential to register your sending domain with Apple. Apple's private email relay service requires authenticated domains to ensure the legitimacy of the sender.

Email marketer from Reddit shares that the bounce error often occurs when an Apple user revokes or disables their private relay address. Implement a process to regularly check for and remove these inactive addresses from your mailing lists.

Marketer from Email Geeks shares that the sending domain may need to be registered with Apple before sending to applerelay.appleid.com addresses, based on a similar issue with a loyalty card provider.

Email marketer from Litmus Community explains that to help resolve the transformation bounces you may need to manually check with the users affected to check their private relay has not expired or been disabled.

Expert from Email Geeks clarifies that the sender addresses need to be registered to prevent bounces.

Expert from Email Geeks explains there was a problem a few days ago causing rejections from the privaterelay.appleid.com servers and Apple is aware and working on a fix.

Expert from Word to the Wise explains that Apple's Private Email Relay service sometimes has issues with email addresses which is server side. They explain to monitor for wider issues by seeing if other senders are reporting similar bounces and if this is the case there is not much you can do to fix the issue yourself.

Expert from Email Geeks suggests confirming compliance with Apple's program rules and sending from the email address registered with Apple for mail to those addresses. It may also mean the userID is not currently valid, and the transformation failure is the failure of the encrypted ID to transform into a valid email address.

Documentation from Apple Developer Documentation explains that the 'transformation error' can occur if there are issues with the private email relay service, especially when users have revoked or disabled their Apple ID email relay addresses. Ensure your application properly handles these scenarios by checking the validity of the email address before sending.

Documentation from SparkPost Documentation highlights that the '5.7.1 transformation error' is often seen when sending to Apple's private relay addresses. This could be because the user has disabled the address, or there is an issue with Apple's service. Check the user's email validity and monitor Apple's service status for any known issues.

Documentation from Mailjet Documentation mentions that one cause of the transformation error is trying to send to invalid or deactivated Apple relay email addresses. Regularly validate email addresses and remove invalid ones from your lists to prevent bounces.