public MailInterface::format(array $message)
Formats a message prior to sending.
Allows to preprocess, format, and postprocess a mail message before it is passed to the sending system. By default, all messages may contain HTML and are converted to plain-text by the Drupal\Core\Mail\Plugin\Mail\PhpMail implementation. For example, an alternative implementation could override the default implementation and also sanitize the HTML for usage in a MIME- encoded email, but still invoking the Drupal\Co