For an App Developer to use with Sign in with Apple with Postmark, there are additional configuration necessary steps necessary. This is because Sign in with Apple allows users to create anonymous email addresses, and Apple has additional requirements to prevent spam.
The steps are:
- Configure DKIM. Apple’s Email Relay requires the email to send with DKIM signed by the sending domain.
- Configure a Custom Return-Path. This feature also requires the MAIL FROM (Return-Path) to match the sending domain.
- Add an SPF Record for Postmark. Generally, Postmark does not require setting up an SPF record, though for Apple’s Private Email Relay to work, an SPF record is required. Postmark’s SPF record to add is:
v=spf1 include:spf.mtasv.net ~all