- Add support for Python 3.6. As of 3.5 (when it became possible), we now
pass the `decode_data=False` parameter when constructing `SMTPChannel` and
`SMTPServer` objects, and handle the new `SMTPServer.process_message`
signature. (LP: #1654334)
- Add support for Python 3.7 and 3.8. We no longer try to raise
StopIteration from a generator. (LP: #1781564)