ines in the
                           body of the message by putting a `>' in front of
                           them. This is used when the message is being
                           serialized by a generator. Default: False.

    message_factory     -- the class to use to create new message objects.
                           If the value is None, the default is Message.

    verify_generated_headers
                        -- if true, the generator verifies that each header
                           they are properly folded, so that a parser won't
                           treat it as multiple headers, start-of-body, or
                           part of another header.
                           This is a check against custom Header & fold()
                           implementations.
    Fr3