Fatal error: Uncaught Error: Class 'Symfony\Component\Mime\Header\AbstractHeader' not found in /mnt/volume_lon1_01/backend/admin/vendor/symfony/mime/Header/MailboxListHeader.php:22 Stack trace: #0 {main} thrown in /mnt/volume_lon1_01/backend/admin/vendor/symfony/mime/Header/MailboxListHeader.php on line 22