The following methods are deprecated in email version 2. They are documented here for completeness.
None
(i.e. never before set), then after this method is called, the payload
will be the argument payload.
If the object's payload was already a list (i.e. is_multipart() returns 1), then payload is appended to the end of the existing payload list.
For any other type of existing payload, add_payload() will transform the new payload into a list consisting of the old payload and payload, but only if the document is already a MIME multipart document. This condition is satisfied if the message's Content-Type: header's main type is either multipart, or there is no Content-Type: header. In any other situation, MultipartConversionError is raised.
If there is no Content-Type: header in the message,
failobj is returned (defaults to None
).