Generator set_boundary m.set_boundary(boundary) Sets the boundary parameter of m 's Content-Type header to boundary . When m has no Content-Type header, raises HeaderParseError . set_payload MIME and Network Encodings m.set_payload(payload) Sets m 's payload to payload , which must be a string or list, as appropriate. set_unixfrom m.set_unixfrom(unixfrom) Sets the envelope header string for m . unixfrom is the entire envelope header line, including the leading ' From ' but not including the trailing ' \n '.