SMTP 'rcpt' command -- indicates 1 recipient for this mail.

def rcpt(self, recip, options=[]):
        """SMTP 'rcpt' command -- indicates 1 recipient for this mail."""
        optionlist = ''
        if options and self.does_esmtp:
            optionlist = ' ' + ' '.join(options)
        code, msg = yield self.docmd(b"rcpt", ("TO:%s%s" % (smtplib.quoteaddr(recip), optionlist)).encode('ascii'))
        return (code, msg)