def get_smtp_header(self):
        """
        Returns the SMTP formatted header of the line.

        :rtype:  string
        :return: The SMTP header.
        """
        header = "From: %s\r\n" % self.get_sender()
        header += "To: %s\r\n" % ',\r\n '.join(self.get_to())
        header += "Cc: %s\r\n" % ',\r\n '.join(self.get_cc())
        header += "Bcc: %s\r\n" % ',\r\n '.join(self.get_bcc())
        header += "Subject: %s\r\n" % self.get_subject()
        return header
Returns the SMTP formatted header of the line.

        :rtype:  string
        :return: The SMTP header.