After successfully sending a message through the relay, we did a test where the user sent a reply back to the reply-to address. The reply-to address looked just like the documenation (https://developer.apple.com/documentation/signinwithapplejs/communicating_using_the_private_email_relay_service#see-also) described: address_at_reply_to_domain@privaterelay.appleid.com
However, when the test was sent, we got an immediate bounce from Gmail, who was trying to send to the private relay:
Reporting-MTA: dns; googlemail.com
Arrival-Date: Wed, 11 Mar 2020 01:08:20 -0700 (PDT)
X-Original-Message-ID: <CALpXbJeDdtdVCqxeO-7n1KYZHSV-AoKhdkWJZt1Lc2wNXWE3_w@mail.gmail.com>
Final-Recipient: rfc822; <redacted>@privaterelay.appleid.com
Action: failed
Status: 5.1.1
Remote-MTA: dns; smtp2.privaterelay.appleid.com. (17.57.9.12, the server for
the domain privaterelay.appleid.com.)
Diagnostic-Code: smtp; 550 5.1.1 Relay not allowed
Last-Attempt-Date: Wed, 11 Mar 2020 01:08:23 -0700 (PDT)The reply-to address domain has the same domain as the from address domain that is authenticated/registered with Apple. Why did we get the "Relay not allowed" bounce?
