v2.0.0

• BREAKING: Drop Python 3.5 and 3.6 support.

• BREAKING: On connect, if the server supports STARTTLS, automatically try
  to upgrade the connection. STARTTLS after connect can be turned on or off
  explicitly by passing start_tls=True or start_tls=False respectively.

• BREAKING: Remove deprecated loop keyword argument for the SMTP class.

• Change: The source_address argument now takes a (addr, port) tuple that is
  passed as the local_addr param to asyncio.create_connection, allowing
  for binding to a specific IP. The new local_hostname argument that takes
  the value to be sent to the server with the EHLO/HELO message. This behaviour
  more closely matches smtplib.

  In order to not break existing usage, passing a string instead of a tuple to
  source_address will give a DeprecationWarning, and use the value as it if
  had been passed for local_hostname.

  Thanks @rafaelrds and @davidmcnabnz for raising and contributing work on this
  issue.

• Bugfix: the mail_options and rcpt_options arguments to the send
  coroutine no longer cause errors

• Cleanup: Refactored SMTP parent classes to remove complex inheritance
  structure.

• Cleanup: Switched to asyncio.run for sync client methods.

• Cleanup: Don't use private email.message.Message policy attribute (instead,
  set an appropriate policy based on message class)