Implement Signing Messages with Symfony Mailer

[MrKrisKrisu]

The package laravel uses for the Mailer (Symfony Mailer) can sign outgouing mails with S/MIME or DKIM. This should be implemented in the Laravel Integration too.

See https://symfony.com/doc/6.2/mailer.html#signing-messages

use Symfony\Component\Mime\Crypto\SMimeSigner;
use Symfony\Component\Mime\Email;

$email = (new Email())
    ->from('[email protected]')
    // ...
    ->html('...');

$signer = new SMimeSigner('/path/to/certificate.crt', '/path/to/certificate-private-key.key');
// if the private key has a passphrase, pass it as the third argument
// new SMimeSigner('/path/to/certificate.crt', '/path/to/certificate-private-key.key', 'the-passphrase');

$signedEmail = $signer->sign($email);
// now use the Mailer component to send this $signedEmail instead of the original email