CIVICRM_MAIL_LOG_AND_SEND does not work properly
In the packages/Mail it is mistyped as "CIVICRM_MAIL_LOG_AND SEND" (ie. missing an underscore): https://github.com/civicrm/civicrm-packages/pull/204
In CiviCRM core the administrator is not notified if it is set: https://github.com/civicrm/civicrm-core/pull/12037
In the docs it is missing altogether: https://github.com/civicrm/civicrm-dev-docs/pull/526
Edited by mattwire