This documents how to successfully use this new feature.
Please see
- https://github.com/civicrm/civicrm-core/pull/19386 (replaced https://github.com/civicrm/civicrm-core/pull/19136 and before that the work begain in Flexmailer at https://github.com/civicrm/org.civicrm.flexmailer/pull/46)
- dev/mail#81 (moved)