castCustomHeader example

$message['ReplyTo'] = $this->formatAddress($emails[0]);
        }
        if ($email->getTextBody()) {
            $message['TextPart'] = $email->getTextBody();
        }
        if ($html) {
            $message['HTMLPart'] = $html;
        }

        foreach ($email->getHeaders()->all() as $header) {
            if ($convertConf = self::HEADER_TO_MESSAGE[$header->getName()] ?? false) {
                $message[$convertConf[0]] = $this->castCustomHeader($header->getBodyAsString(), $convertConf[1]);
                continue;
            }
            if (\in_array($header->getName(), self::FORBIDDEN_HEADERS, true)) {
                continue;
            }

            $message['Headers'][$header->getName()] = $header->getBodyAsString();
        }

        return [
            'Messages' => [$message],