[RFC] Add extra ehlo() and starttls() for gmail smtp

[Aaron Bentley]

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Harald Meland wrote:
> [Keir Mierle]
> An SMTP client shouldn't try to do STARTTLS until after EHLO has
> succeeded (and indicated that STARTTLS indeed is among the extensions
> that the server supports).  The client should also fall back to HELO
> if EHLO fails, and verify whether HELO fails.

This looks like a nice improvement.  There's just one thing I wonder about:

> +                (code, message) = self._connection.starttls()
> +                if (200 <= code <= 299):

This seems to mean that if starttls fails, we'll use unencrypted SMTP.
I'm not sure whether we should fail in this situation, give a warning,
or silently continue.  It seems like if people expect their privacy to
be protected and it's not, that's a violation of trust.  But OTOH, I
don't know whether people would expect privacy here.

Aaron
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