Feature: #93689 - PSR-14 events on sending messages with Mailer 

Description 

TYPO3's MailerInterface implementation Mailer is used for sending messages, e.g. in the EXT:form email finishers. To allow further handling and manipulation of the message sending process, two new PSR-14 events have been introduced.

The BeforeMailerSentMessageEvent is dispatched before the message is sent by the mailer and can be used to manipulate the RawMessage and the Envelope . Usually an Email or FluidEmail instance is given as RawMessage . Additionally, the MailerInstance is given, which depending on the implementation - usually \TYPO3\CMS\Core\Mail\Mailer - contains the Transport object, which can be retrieved using the getTransport() method.

The AfterMailerSentMessageEvent is dispatched as soon as the message has been sent via the corresponding TransportInterface . The event receives the current MailerInstance , which, depending on the implementation - usually \TYPO3\CMS\Core\Mail\Mailer - contains the SentMessage object that can be retrieved using the getSentMessage() method.

Registration of the event listeners in your extension's Services.yaml:

MyVendor\MyPackage\EventListener\MailerSentMessageEventListener:
  tags:
    - name: event.listener
      identifier: 'my-package/modify-message'
      method: 'modifyMessage'
    - name: event.listener
      identifier: 'my-package/process-sent-message'
      method: 'processSentMessage'

The corresponding event listener class:

use Psr\Log\LoggerInterface;
use Symfony\Component\Mime\Address;
use Symfony\Component\Mime\Email;
use TYPO3\CMS\Core\Mail\Event\AfterMailerSentMessageEvent;
use TYPO3\CMS\Core\Mail\Event\BeforeMailerSentMessageEvent;
use TYPO3\CMS\Core\Mail\Mailer;

final class MailerSentMessageEventListener
{
    public function __construct(
        private readonly LoggerInterface $logger
    ) {
    }

    public function modifyMessage(BeforeMailerSentMessageEvent $event): void
    {
        $message = $event->getMessage();

        // If $message is an Email implementation, add an additional recipient
        if ($message instanceof Email) {
            $message->addCc(new Address('kasperYYYY@typo3.org'));
        }
    }

    public function processSentMessage(AfterMailerSentMessageEvent $event): void
    {
        $mailer = $event->getMailer();
        if ($mailer instanceof Mailer) {
            $sentMessage = $mailer->getSentMessage();
            if ($sentMessage !== null) {
                $this->logger->debug($sentMessage->getDebug());
            }
        }
    }
}

Impact 

With the new PSR-14 events, it's now possible to manipulate messages before they are sent by the mailer. Additionally, after the mailer has sent messages, further processing can be performed.