The hook alterMailParams is not called from CiviMail

civicrm$ grep -R alterMailParams .
./CRM/Utils/Mail.php: CRM_Utils_Hook::alterMailParams( $params );
./CRM/Utils/Hook.php: static function alterMailParams( &$params ) {
./CRM/Utils/Hook.php: '::invoke( 1, $params, $null, $null, $null, $null, \'civicrm_alterMailParams\' );' );

=> alterMailParams does not get called from Job, only from CRM/Utils/Mail.php