Fatal error: Uncaught Error: Class 'Zend\Mail\Header\GenericHeader' not found in /home/optinadmin/rfl.optin.co.nz/concrete/vendor/zendframework/zend-mail/src/Header/GenericMultiHeader.php:15 Stack trace: #0 {main} thrown in /home/optinadmin/rfl.optin.co.nz/concrete/vendor/zendframework/zend-mail/src/Header/GenericMultiHeader.php on line 15