I'm having an issue when upgrading my PHP version to 7.2 to get ready for a system upgrade to Magento 2.4 and the backend email system stops working. I don't receive new order emails and can't send out comment emails to customers. Any ideas?
If you are using any SMTP Module such as Mageplaza SMTP for the Emails then update those modules with the new one, because they having some updated files for the Magento 2.4 Version.
Mageplaza SMTP: https://github.com/mageplaza/magento-2-smtp
Also the Mageplaza Core: https://github.com/mageplaza/module-core
If it works then do share an update.