smtplib's "complex" methods, login and sendmail, try to EHLO or HELO if it hasn't been done yet. login also checks to see if the EHLO response included the ability to do authorization. starttls seems to me to be similar in nature: why should it not try to EHLO or HELO, and check that self.has_extn("starttls")?
I've attached a patch against 2.4.3. The patch does the following: - Factor out the duplication of EHLO/HELO in login() and sendmail() to a new function, ehlo_or_helo_if_needed(). - Use ehlo_or_helo_if_needed() in starttls() - Check for the starttls exception in starttls() in the same way as login() checks for the auth extension.
From RFC 2487 section 5.2: "The client MUST discard any knowledge obtained from the server, such as the list of SMTP service extensions, which was not obtained from the TLS negotiation itself. The client SHOULD send an EHLO command as the first command after a successful TLS negotiation." So the starttls() method should probably also be clearing helo_resp and ehlo_resp (and maybe anything else discovered by ehlo()). There are servers in the wild that will (a) refuse to talk to you unless you issue another EHLO after TLS is negotiated and (b) offer a different set of ESMTP features (such as only supporting SMTP AUTH after TLS). This patch isn't enough to talk to such servers.
