When using smtplib.SMTP to connect to a SMTP server the instance variables esmtp_response survives a SMTP.quit() which results in the following error: >>> import smtplib >>> smtp = smtplib.SMTP('mail.oberkirch.org', 25) >>> smtp.starttls() (220, b'2.0.0 Ready to start TLS') >>> smtp.ehlo() (250, b'mail.oberkirch.org\nPIPELINING\nSIZE 10240000\nVRFY\nETRN\nAUTH PLAIN LOGIN\nAUTH=PLAIN LOGIN\nENHANCEDSTATUSCODES\n8BITMIME\nDSN') >>> smtp.quit() (221, b'2.0.0 Bye') >>> smtp.connect('mail.oberkirch.org', 25) (220, b'mail.oberkirch.org ESMTP Postfix') >>> smtp.starttls() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python3.4/smtplib.py", line 672, in starttls raise SMTPException("STARTTLS extension not supported by server.") smtplib.SMTPException: STARTTLS extension not supported by server. >>> While reporting this issue I found out that starttls also does not throw away any ehlo information as it should. Provided that fixing this would probably break existing code (which would only work with non-standard servers like postfix) I did not change that behaviour.

Thanks, Milan. I could swear I typed a '6' in the commit message, but apparently not... New changeset a058760cb069 by R David Murray in branch '3.4': #22215: have the smtplib 'quit' command reset the state. http://hg.python.org/cpython/rev/a058760cb069 New changeset d0d4ab0ba70e by R David Murray in branch 'default': Merge #22215: have the smtplib 'quit' command reset the state. http://hg.python.org/cpython/rev/d0d4ab0ba70e New changeset 7288519594de by R David Murray in branch '2.7': #22215: have the smtplib 'quit' command reset the state. http://hg.python.org/cpython/rev/7288519594de