Fatal error: Uncaught Error: Class "Symfony\Component\Mime\Header\AbstractHeader" not found in /home/custom/public_html/katiekarr/vendor/symfony/mime/Header/MailboxListHeader.php:22 Stack trace: #0 {main} thrown in /home/custom/public_html/katiekarr/vendor/symfony/mime/Header/MailboxListHeader.php on line 22