c field, when the Message is a
        resent) of the Message object won't be transmitted.  The Message
        object is then serialized using email.generator.BytesGenerator and
        sendmail is called to transmit the message.  If the sender or any of
        the recipient addresses contain non-ASCII and the server advertises the
        SMTPUTF8 capability, the policy is cloned with utf8 set to True for the
        serialization, and SMTPUTF8 and BODY=8BITMIME are asserted on the send.
        If the server does not support SMTPUTF8, an SMTPNotSupported error is
        raised.  Otherwise the generator is called without modifying the
        policy.

        z