public function setTo($to)
    {
        if ($to instanceof Email) {
            $to = [$to];
        }

        foreach ($to as $email) {
            if (!$email instanceof Email) {
                throw new MailerException('Email must be an instance of \Webiny\Component\Mailer\Email.');
            }
            $this->addTo($email);
        }

        return $this;
    }