Upstream have removed the legacy mail configs which affects us. We need to migrate to cluster.mailers (to continue to get updates from upstream).
they now include "void-recipient@<domain>" in the email https://github.com/phacility/phabricator/blob/73e3057c52f46ec6ddb75fc495a03255c5199c16/src/applications/metamta/storage/PhabricatorMetaMTAMail.php#L1474
looked at upstream docs, config change looks ok to me, confirmed with @herron services should use smtp to localhost and this does just that.
paladox tested on wmcs that phabricator still sends out mail and the metamta.* options are unffected, so domain and no-reply@ address are unchanged